0000950170-24-021787 | 10-K | XBRL Viewer

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Segment Information - Schedule of Segment Revenues for Significant Product Lines (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net sales	$ 2,154.2	$ 1,980.5	$ 1,678.6
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Net sales	116.3	96.5	91.2
Railroad and Utility Products and Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	897.9	788.3	729.9
Railroad and Utility Products and Services [Member] \| Railroad Treated Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	540.9	457.4	414.4
Railroad and Utility Products and Services [Member] \| Utility Poles [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	266.1	227.9	228.0
Railroad and Utility Products and Services [Member] \| Railroad Infrastructure Products and Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	90.9	103.0	87.5
Carbon Materials and Chemicals [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Net sales	87.4	74.3	75.3
Carbon Materials and Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	584.7	612.3	445.4
Carbon Materials and Chemicals [Member] \| Pitch and Related Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	394.4	399.6	279.3
Carbon Materials and Chemicals [Member] \| Phthalic Anhydride, Naphthalene and Other Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	112.0	148.4	110.2
Carbon Materials and Chemicals [Member] \| Carbon Black Feedstock and Distillates [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	78.3	64.3	55.9
Performance Chemicals [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Net sales	28.9	22.2	15.9
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	671.6	579.9	503.3
Performance Chemicals [Member] \| Other Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	24.4	18.7	14.2
Performance Chemicals [Member] \| Wood Preservative Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	$ 647.2	$ 561.2	$ 489.1

Acquisitions, Divestitures and Discontinued Operations - Schedule of Fair Value of Assets and Liabilities Acquired (Detail) - Gross & Janes Co [Member] $ in Millions	Oct. 31, 2022 USD ($)
Business Acquisition [Line Items]
Accounts receivable	$ 4.3
Inventory	7.4
Property, plant and equipment	4.5
Total assets acquired	16.2
Accounts payable and accrued liabilities	0.7
Net assets acquired	$ 15.5

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023 shares
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	On December 20, 2023, Leslie S. Hyde, Senior Vice President and Chief Sustainability Officer (an officer of the Company as defined in Rule 16a-1(f) of the Securities and Exchange Act of 1934), adopted a trading plan (the Plan) intended to satisfy the affirmative defense of Rule 10b5-1(c) of the Securities Exchange Act of 1934. The Plan provides for the exercise of 7,962 options (granted on March 6, 2019 and set to expire on March 5, 2029) and 14,441 options (granted on March 3, 2020 and set to expire on March 2, 2030) to purchase shares of the Company's stock and the subsequent sale of the shares received from the exercise of such options. The Plan will commence on March 21, 2024, and terminate on the earlier of (i) November 29, 2024, (ii) the execution of all trades contemplated by the Plan, or (iii) the valid exercise of termination rights under the Plan by either Leslie S. Hyde or the broker of the Plan. During the three months ended December 31, 2023, none of our other directors or executive officers adopted or terminated any Rule 10b5-1 trading arrangement or any non-Rule 10b5-1 trading arrangement (as such terms are defined in Item 408 of Regulation S-X).
Leslie S. Hyde
Trading Arrangements, by Individual
Name	Leslie S. Hyde
Title	Senior Vice President and Chief Sustainability Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	December 20, 2023
Termination Date	November 29, 2024
Arrangement Duration	253 days
Other Directors or Executive Officers
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Stock Option Granted on March 6, 2019 \| Leslie S. Hyde
Trading Arrangements, by Individual
Aggregate Available	7,962
Stock Option Granted on March 3, 2020 \| Leslie S. Hyde
Trading Arrangements, by Individual
Aggregate Available	14,441

Description of Business - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2023 Segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	3

Debt - Additional Information (Detail) - USD ($)			12 Months Ended
Debt - Additional Information (Detail) - USD ($)	Oct. 11, 2023	Apr. 10, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Revolving credit facility			$ 730,000,000
Long term debt			849,400,000	$ 825,300,000
Term Loan B [Member]
Debt Instrument [Line Items]
Long term debt			388,000,000.0	$ 0.0
Senior Secured Credit Facilities [Member]
Debt Instrument [Line Items]
Letters of credit, amount outstanding			$ 8,600,000
Commitment fees on undrawn portion of credit facility			0.22%	0.22%	0.25%
Senior Notes due 2025 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long term debt			$ 0.0	$ 500,000,000.0
Revolving Credit Agreement [Member]
Debt Instrument [Line Items]
Revolving credit facility			800,000,000
Swingline Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility			50,000,000
Credit Facility [Member] \| Senior Secured Credit Facilities [Member]
Debt Instrument [Line Items]
Debt instrument, unused borrowing capacity			$ 330,000,000
Amendment No. 1 to Credit Facility [Member] \| Term Loan B [Member]
Debt Instrument [Line Items]
Secured term loan		$ 400,000,000
Percentage of face value of issued debt		97.00%
Net proceeds from secured debt, before debt financing costs		$ 388,000,000
Amendment Number 2 To Credit Facility [Member] \| Term Loan B [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	3.50%
Debt instrument, floor interest rate	0.50%
Debt instrument, payment terms	the principal balance of the Term Loan B is repayable in quarterly installments in an amount equal to 0.25 percent of the principal amount, commencing on January 1, 2024 and on the last business day of each quarterly period thereafter, with the balance due at maturity on April 10, 2030.
Debt instrument, percentage of principal payment	0.25%
Debt instrument, frequency of periodic payment	quarterly
Debt maturity date	Apr. 10, 2030

Goodwill and Other Identifiable Intangible Assets - Schedule of Future Amortization Expense (Detail) $ in Millions	Dec. 31, 2022 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2024	$ 14.2
2025	13.7
2026	12.4
2027	12.0
2028	$ 11.2

Summary of Significant Accounting Policies - Summary of Asset Retirement Obligation Liabilities (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Asset Retirement Obligation Disclosure [Abstract]
Asset retirement obligation at beginning of year	$ 15.5	$ 13.2
Accretion expense	1.1	1.1
Revision in estimated cash flows (a)	(0.8)	2.2
Cash expenditures	(0.6)	(1.0)
Balance at end of period	$ 15.2	$ 15.5

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,104.9	$ 1,019.4
Less accumulated depreciation	473.2	462.1
Property, plant and equipment, net	631.7	557.3
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	18.8	15.0
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	99.1	80.3
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 987.0	$ 924.1

Pensions and Post-Retirement Benefit Plans - Schedule of Projected Benefit Payments (Detail) $ in Millions	Dec. 31, 2023 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2024	$ 11.4
2025	11.8
2026	11.3
2027	11.2
2028	11.5
Next five years	57.3
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2024	0.5
2025	0.5
2026	0.5
2027	0.5
2028	0.5
Next five years	$ 2.4

Stock-based Compensation - Summary of Status and Activity of Stock Options (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) $ / shares shares
Share-Based Payment Arrangement [Abstract]
Options, Outstanding at December 31, 2022 \| shares	1,122,136
Options, Exercised \| shares	(365,237)
Options, Expired \| shares	(50,031)
Options, Outstanding at December 31, 2023 \| shares	706,868
Options, Exercisable at December 31, 2023 \| shares	545,392
Weighted Average Exercise Price per Option, Outstanding at December 31, 2022 \| $ / shares	$ 27.05
Weighted Average Exercise Price per Option, Exercised \| $ / shares	24.11
Weighted Average Exercise Price per Option, Expired \| $ / shares	42.16
Weighted Average Exercise Price per Option, Outstanding at December 31, 2023 \| $ / shares	27.51
Weighted Average Exercise Price per Option, Exercisable at December 31, 2023 \| $ / shares	$ 27.29
Weighted Average Remaining Contractual Term, Outstanding at December 31, 2023	5 years 7 days
Weighted Average Remaining Contractual Term, Exercisable at December 31, 2023	4 years 4 months 6 days
Aggregate Intrinsic Value, Outstanding at December 31, 2023 \| $	$ 16.8
Aggregate Intrinsic Value, Exercisable at December 31, 2023 \| $	$ 13.0

Goodwill and Other Identifiable Intangible Assets

12 Months Ended

Dec. 31, 2023

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Other Identifiable Intangible Assets

13. Goodwill and Intangible Assets

Goodwill and other purchased intangible assets are included in the identifiable assets of the business segment to which they have been assigned. Goodwill is assessed for impairment annually, using a quantitative goodwill impairment test, or more frequently if a change in circumstances or the occurrence of significant events indicate the carrying value may not be recoverable. In making this assessment, management may first consider qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. Examples of qualitative factors include macroeconomic conditions, industry and market considerations, cost factors, overall financial performance, entity-specific events, events affecting reporting units, and sustained changes in our stock price.

If results of the qualitative assessment indicate a more likely than not determination or if a qualitative assessment is not performed, a quantitative test is performed utilizing a combination of an income approach, using a discounted cash flow methodology, and a market approach, by comparing the estimated fair value of each reporting unit with its net book value.

The discounted cash flow calculations are dependent on several key assumptions including the timing of future forecasted cash flows, forecasted revenue growth rates, forecasted EBITDA margin and the discount rate. The market approach uses the guideline company method, which involves calculating valuation multiples based on financial data from comparable publicly traded companies. Multiples derived from these companies provide an indication of how much a knowledgeable investor in the marketplace would be willing to pay for a company. These multiples are then applied to the financial data for our reporting units to arrive at an indication of value. To determine the reasonableness of the calculated fair values of our reporting units, we review the assumptions described to ensure neither the market approach nor the income approach yields significantly different valuations. We selected these valuation approaches because we believe the combination of these approaches, along with our best judgment regarding underlying assumptions and estimates, provides us with the best estimate of fair value of our reporting units.

We perform an assessment of goodwill at the reporting unit level. We have three reporting units for purposes of goodwill evaluation. These units consist of our PC operating segment, our Railroad Products and Services reporting unit and our Utility Products reporting unit. Railroad Products and Services and Utility Products are one level below our RUPS operating segment. The Railroad Products and Services reporting unit primarily serves the rail industry in North America, and the Utility Products reporting unit serves the utility industries in the United States and Australia.

We have historically performed our annual goodwill impairment test as of November 30 each year. During the year ended December 31, 2023, we voluntarily changed our annual impairment assessment date from November 30 to October 31. No more than twelve months have elapsed between goodwill impairment tests of any of our reporting units. The change in measurement date represents a voluntary change in the method of applying an accounting principle that was applied prospectively. The change aligns the annual impairment test date with our forecasting process. We continue to monitor each reporting unit for triggering events for purposes of goodwill impairment testing each quarter. The change in accounting principle did not result in any delay, acceleration or avoidance of an impairment charge. We determined that the estimated fair values exceeded the carrying values of all the reporting units, and accordingly, there was no impairment of goodwill incurred for each of the three years ended December 31, 2023.

The change in the carrying amount of goodwill attributable to each reporting unit was as follows:


	Performance Chemicals			Railroad Products and Services			Utility Products			Total
(Dollars in millions)
Balance at December 31, 2021	$	175.1		$	41.1		$	79.8		$	296.0
Currency translation		(1.7	)		(0.1	)		(0.2	)		(2.0	)
Balance at December 31, 2022	$	173.4		$	41.0		$	79.6		$	294.0
Currency translation		0.4			0.0			0.0			0.4
Balance at December 31, 2023	$	173.8		$	41.0		$	79.6		$	294.4

Intangible assets, other than goodwill, are recorded at fair value and amortized on a straight-line basis over their estimated useful lives. We annually evaluate the remaining useful life of the intangible asset being amortized to determine whether events or circumstances warrant a revision to the remaining period of amortization. If the estimate of an intangible asset’s remaining useful life is changed, the remaining carrying amount of the intangible asset will be amortized prospectively over that revised remaining useful life. Intangible assets are also subject to testing for recoverability whenever events or changes indicate that its carrying value may not be recoverable.

Our intangible assets are summarized below:


					December 31,
					2023						2022
	Estimated life in years		Weighted average remaining life in years		Gross Carrying Amount		Accumulated Amortization		Net		Gross Carrying Amount		Accumulated Amortization		Net
(Dollars in millions)
Customer contracts	9 to 18			8.1	$	225.4	$	125.2	$	100.2	$	224.9	$	110.5	$	114.4
Technology	4 to 12			2.6		26.4		26.1		0.3		26.4		26.0		0.4
Trademarks	4 to 18			11.2		8.2		6.5		1.7		7.7		6.5		1.2
Supply contracts		10		0.0		2.4		2.4		0.0		2.4		2.4		0.0
Non-compete agreements		12		0.8		1.6		1.6		0.0		1.6		1.5		0.1
Total				8.1	$	264.0	$	161.8	$	102.2	$	263.0	$	146.9	$	116.1

In 2023, the gross carrying value of intangible assets increased by a net $1.0 million, primarily due to foreign exchange translation. Total amortization expense related to these intangible assets was $14.5 million, $14.9 million and $18.3 million for the years ended December 31, 2023, 2022 and 2021, respectively. Estimated amortization expense for the next five years is summarized below:


	Estimated annual amortization
(Dollars in millions)
2024	$	14.2
2025		13.7
2026		12.4
2027		12.0
2028		11.2

Derivative Financial Instruments - Summary of Net Currency Units Outstanding (Detail)	Dec. 31, 2023 AUD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 AUD ($)	Dec. 31, 2022 USD ($)
Offsetting [Abstract]
Net currency units outstanding	$ 3,000,000	$ 10,300,000	$ 3,000,000	$ 9,300,000

Stock-based Compensation - Stock Options Fair Value Assumptions (Detail)	12 Months Ended
	Dec. 31, 2023 $ / shares
January 2022 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock option award	$ 32.19
Expected life in years	6 years 9 months 3 days
Expected volatility	54.50%
Risk-free interest rate	1.52%
Grant date fair value per share of stock option award	$ 17.58
January 2021 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock option award	$ 29.84
Expected life in years	6 years 7 months 20 days
Expected volatility	54.80%
Risk-free interest rate	0.59%
Grant date fair value per share of stock option award	$ 15.79
March 2020 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock option award	$ 19.63
Expected life in years	6 years 4 months 24 days
Expected volatility	42.85%
Risk-free interest rate	0.87%
Grant date fair value per share of stock option award	$ 8.42

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Pensions and Post-Retirement Benefit Plans - Schedule of Change in Funded Status of Pension and Post-Retirement Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Actuarial (gains) losses	$ (2.1)
Fair value of plan assets at beginning of year	127.4
Fair value of plan assets at end of year	128.1	$ 127.4
Noncurrent liabilities	31.6	34.7
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	157.0	219.6
Service cost	1.6	1.2	$ 1.5
Interest cost	8.2	5.6	5.2
Actuarial (gains) losses	(2.1)	(51.8)
Settlements	(1.1)	(1.0)
Currency translation	1.9	(5.8)
Benefits paid	(11.2)	(10.8)
Benefit obligation at end of year	154.3	157.0	219.6
Fair value of plan assets at beginning of year	127.4	190.0
Actual return on plan assets	9.2	(46.1)
Employer contribution	1.9	0.9
Settlements	(1.1)	(1.0)
Currency translation	1.9	(5.6)
Benefits paid	(11.2)	(10.8)
Fair value of plan assets at end of year	128.1	127.4	190.0
Funded status of the plan	(26.2)	(29.6)
Benefit obligation	152.6	154.4
Fair value of plan assets	125.8	124.2
Accumulated benefit obligation	152.4	154.2
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	6.0	9.8
Service cost	0.0	0.0	0.1
Interest cost	0.3	0.3	0.3
Actuarial (gains) losses	0.7	(3.4)
Settlements	0.0	0.0
Currency translation	0.0	0.0
Benefits paid	(0.8)	(0.7)
Benefit obligation at end of year	6.2	6.0	9.8
Fair value of plan assets at beginning of year	0.0	0.0
Actual return on plan assets	0.0	0.0
Employer contribution	0.8	0.7
Settlements	0.0	0.0
Currency translation	0.0	0.0
Benefits paid	(0.8)	(0.7)
Fair value of plan assets at end of year	0.0	0.0	$ 0.0
Funded status of the plan	$ (6.2)	$ (6.0)

Plant Closure and Divestitures - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Mar. 31, 2022	Oct. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Restructuring Cost And Reserve [Line Items]
Gain on sale			$ 1.8	$ 2.5	$ 31.2
Railroad and Utility Products and Services [Member] \| Facility [Member]
Restructuring Cost And Reserve [Line Items]
Gain on sale		$ 23.4
Sweetwater, Tennessee [Member] \| Pole Treating Facility [Member]
Restructuring Cost And Reserve [Line Items]
Gain on sale	$ 2.5

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Consolidated Statement of Operations - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Net sales	$ 2,154.2	$ 1,980.5	$ 1,678.6
Cost of sales	1,729.7	1,635.9	1,344.5
Depreciation and amortization	57.0	56.1	57.7
Selling, general and administrative expenses	174.1	153.3	148.9
Impairment and restructuring charges	0.0	0.0	2.2
(Gain) on sale of assets	(1.8)	(2.5)	(31.2)
Operating profit	195.2	137.7	156.5
Other income, net	0.4	2.5	3.6
Interest expense	71.0	44.8	40.5
Income from continuing operations before income taxes	124.6	95.4	119.6
Income tax provision	34.8	31.6	34.5
Income from continuing operations	89.8	63.8	85.1
Loss on sale of discontinued operations	0.0	(0.6)	(0.2)
Net income	89.8	63.2	84.9
Net income (loss) attributable to noncontrolling interests	0.6	(0.2)	(0.3)
Net income attributable to Koppers	$ 89.2	$ 63.4	$ 85.2
Basic -
Continuing operations	$ 4.28	$ 3.05	$ 4.02
Discontinued operations	0.00	(0.03)	(0.02)
Earnings per basic common share	4.28	3.02	4.00
Diluted -
Continuing operations	4.14	3.00	3.90
Discontinued operations	0.00	(0.02)	(0.02)
Earnings per diluted common share	$ 4.14	$ 2.98	$ 3.88
Weighted average shares outstanding (in thousands):
Basic	20,835	20,977	21,238
Diluted	21,539	21,313	21,925

Earnings and Dividends per Common Share - Schedule of Computation of Basic and Diluted Earnings per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net income attributable to Koppers	$ 89.2	$ 63.4	$ 85.2
Loss on sale of discontinued operations	0.0	(0.6)	(0.2)
Income from continuing operations attributable to Koppers	$ 89.2	$ 64.0	$ 85.4
Weighted average common shares outstanding:
Basic	20,835	20,977	21,238
Effect of dilutive securities	704	336	687
Diluted	21,539	21,313	21,925
Earnings per common share – continuing operations:
Basic earnings per common share	$ 4.28	$ 3.05	$ 4.02
Diluted earnings per common share	$ 4.14	$ 3.00	$ 3.90
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share	315	952	436

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Summary of Income Tax Provision

Components of our income tax provision are as follows:


	Year Ended December 31,
	2023		2022			2021
(Dollars in millions)
Current:
Federal	$	7.3	$	0.0		$	(1.5	)
State		1.7		0.6			0.9
Foreign		20.1		28.4			18.2
Total current tax provision		29.1		29.0			17.6
Deferred:
Federal		3.1		0.2			10.6
State		0.6		(0.6	)		1.1
Foreign		2.0		3.0			5.2
Total deferred tax provision		5.7		2.6			16.9
Total income tax provision	$	34.8	$	31.6		$	34.5

Summary of Income Taxes Reconciled with Federal Statutory Rate

The provision for income taxes is reconciled with the federal statutory income tax rate as follows:


	Year Ended December 31,
	2023			2022			2021
Federal income tax rate		21.0	%		21.0	%		21.0	%
Foreign earnings taxed at different rates		4.9			8.7			4.3
State income taxes, net of federal tax benefit		1.4			(0.2	)		2.1
GILTI inclusion, net of foreign tax credits		0.2			1.7			0.2
Change in tax contingency reserves		0.2			(0.1	)		(1.1	)
Valuation allowance adjustments		0.0			0.9			1.9
Deferred tax adjustments		0.0			0.0			(0.2	)
Other		0.2			1.1			0.6
		27.9	%		33.1	%		28.8	%

Summary of Deferred Tax Assets and Liabilities

Significant components of our deferred tax assets and liabilities are as follows:


	Year Ended December 31,
	2023			2022
(Dollars in millions)
Deferred tax assets:
Federal and state tax loss carryforwards, expiring in 2024 to 2043	$	19.2		$	22.6
Tax credits		16.9			17.4
Reserves, including insurance and environmental		10.4			9.3
Interest disallowance		10.2			6.4
Accrued employee compensation		8.1			6.5
Inventory		7.6			4.6
Foreign tax loss carryforwards		7.4			6.6
Pension and other post-retirement benefits obligations		7.2			8.2
Asset retirement obligations		5.6			5.3
Other		8.3			4.6
Valuation allowance		(43.1	)		(43.8	)
Total deferred tax assets		57.8			47.7
Deferred tax liabilities:
Tax over book depreciation and amortization		69.9			52.3
Gain on derivative contracts		0.0			0.7
Other		3.4			4.5
Total deferred tax liabilities		73.3			57.5
Net deferred tax liabilities	$	(15.5	)	$	(9.8	)

Summary of Valuation Allowances Recorded to Offset Deferred Tax Assets

A valuation allowance is necessary when it is more likely than not that a deferred tax asset will not be realized. Certain deferred tax assets reflected above are not expected to be realized, and a valuation allowance has been provided for them.

Valuation allowances are recorded to offset the following deferred tax assets:


	December 31,
	2023		2022
(Dollars in millions)
State temporary differences, net operating losses and tax credits	$	19.3	$	19.4
Federal foreign tax credits		15.2		16.1
Foreign temporary differences, net operating losses and capital losses		8.6		8.3
Total valuation allowances	$	43.1	$	43.8

Summary of Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:


	December 31,
	2023			2022			2021
(Dollars in millions)
Balance at beginning of year	$	1.4		$	1.5		$	2.5
Additions based on tax provisions related to the current year		0.3			0.1			0.1
Reductions resulting from a lapse in the statute of limitations		(0.2	)		(0.2	)		(1.1	)
Balance at end of year	$	1.5		$	1.4		$	1.5

Income taxes - Summary of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 1.4	$ 1.5	$ 2.5
Additions based on tax provisions related to the current year	0.3	0.1	0.1
Reductions resulting from a lapse in the statute of limitations	(0.2)	(0.2)	(1.1)
Balance at end of year	$ 1.5	$ 1.4	$ 1.5

Derivative Financial Instruments - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) Gallons
Derivative [Line Items]
Maximum period hedged in cash flow hedge	36 months
Unrealized gains, reclassification period	12 months
Number of derivative contract \| Gallons	1,500,000
Net fair value of a liability	$ 0.3
Interest Rate Swaps [Member]
Derivative [Line Items]
Unrealized gains, net of tax, expected to be reclassified from other comprehensive income into earnings	2.1
Derivative, notional value	$ 400.0
Fixed interest rate of loan portion	3.97%
Interest rate margin	3.50%
Derivative, maturity date	Apr. 30, 2027
Commodity Price Hedging [Member]
Derivative [Line Items]
Unrealized gains, net of tax, expected to be reclassified from other comprehensive income into earnings	$ 2.0

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Schedule of Company's Financial Instruments

The following table presents the estimated fair values and the related carrying amounts of our financial instruments:


	December 31, 2023				December 31, 2022
	Fair Value		Carrying Value		Fair Value		Carrying Value
(Dollars in millions)
Financial assets:
Investments and other assets	$	1.3	$	1.3	$	1.3	$	1.3
Financial liabilities:
Long-term debt (including current portion)	$	860.4	$	849.4	$	801.1	$	825.3

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Summary Of Significant Accounting Policies [Line Items]
Period for payment terms on ship and invoice arrangements.	45 days
Period for payment of approval basis sale	30 days
Contract Assets	$ 7.8	$ 8.3
Percentage of LIFO inventory	58.00%	52.00%
Inventory write-down	$ 0.6	$ 1.2	$ 0.6
Buildings [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	10 years
Buildings [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	20 years
Machinery and Equipment [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Machinery and Equipment [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	15 years

Consolidated Statement of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash provided by (used in) operating activities:
Net income	$ 89.8	$ 63.2	$ 84.9
Adjustments to reconcile net cash provided by (used in) operating activities:
Depreciation and amortization	57.0	56.1	57.7
Stock-based compensation	17.3	13.2	13.0
Change in derivative contracts	(0.9)	6.5	3.8
Non-cash interest expense	4.9	2.8	2.7
(Gain) on sale of assets and investment	(2.0)	(2.6)	(31.2)
Insurance proceeds	(1.7)	(0.8)	(6.1)
Deferred income taxes	5.7	2.7	16.9
Change in other liabilities	0.2	1.1	2.1
Other - net	2.2	5.3	4.0
Changes in working capital:
Accounts receivable	14.9	(32.3)	(12.7)
Inventories	(37.2)	(41.8)	(24.3)
Accounts payable	(0.4)	32.7	20.9
Accrued liabilities	(2.4)	(7.3)	(21.0)
Other working capital	(1.3)	3.5	(7.7)
Net cash provided by operating activities	146.1	102.3	103.0
Cash (used in) provided by investing activities:
Capital expenditures	(120.5)	(105.3)	(125.0)
Insurance proceeds	1.7	0.8	6.1
Acquisitions	0.0	(14.7)	0.0
Net cash provided by sale of discontinued operations and asset sales	2.8	4.4	29.4
Net cash used in investing activities	(116.0)	(114.8)	(89.5)
Cash provided by (used in) financing activities:
Borrowings of credit facility	1,032.5	444.4	280.9
Repayments of credit facility	(896.4)	(406.1)	(265.7)
Borrowings of long-term debt	388.0	0.0	0.0
Repayments of long-term debt	(501.0)	(2.0)	(10.1)
Issuances of Common Stock	9.9	1.1	2.4
Repurchases of Common Stock	(20.1)	(23.6)	(11.5)
Payment of debt issuance costs	(5.3)	(4.8)	0.0
Dividends paid	(5.0)	(4.2)	0.0
Net cash provided by (used in) financing activities	2.6	4.8	(4.0)
Effect of exchange rate changes on cash	0.5	(4.5)	(2.5)
Net increase (decrease) in cash and cash equivalents	33.2	(12.2)	7.0
Cash and cash equivalents at beginning of period	33.3	45.5	38.5
Cash and cash equivalents at end of period	66.5	33.3	45.5
Supplemental disclosure of non-cash investing and financing activities:
Right-of-use assets obtained in exchange for new operating lease liabilities	26.6	12.1	12.6
Accrued capital expenditures	5.6	11.1	7.3
Cash paid during the year for:
Interest	70.0	41.3	38.1
Income taxes	$ 34.3	$ 20.7	$ 23.4

Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Schedule of Operating Lease Costs, Variable Lease Costs and Supplemental Cash Flow Information

The following table presents operating lease costs, variable lease costs and supplemental cash flow information:


	Year Ended December 31,
	2023		2022		2021
(Dollars in millions)
Operating lease costs	$	28.7	$	29.3	$	30.2
Variable lease costs		4.0		3.3		3.3
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash outflow from operating leases	$	39.5	$	29.3	$	30.5

Summary of Amount and Timing of Cash Flows From Operating Leases

The following table presents information about the amount and timing of cash flows arising from our operating leases as of December 31, 2023:


(Dollars in millions)
2024	$	28.2
2025		22.8
2026		17.7
2027		14.7
2028		11.7
Thereafter		12.5
Total lease payments	$	107.6
Less: Interest		(17.3	)
Present value of lease liabilities	$	90.3

Schedule of Supplemental Consolidated Balance Sheet Information Related to Leases

Supplemental consolidated balance sheet information related to leases is as follows:


	December 31,
	2023			2022
Weighted average remaining lease term, in years		5.0			5.6
Weighted average discount rate		6.8	%		7.2	%

Debt

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Debt

15. Debt


					December 31,
	Weighted Average Interest Rate			Maturity	2023		2022
(Dollars in millions)
Credit Facility		7.39	%	2027	$	461.4	$	325.3
Term Loan B		7.56	%	2030		388.0		0.0
Senior Notes due 2025	-			-		0.0		500.0
Total debt						849.4		825.3
Less short-term debt and current maturities of long-term debt						5.0		0.0
Less unamortized debt issuance costs						9.0		7.6
Long-term debt					$	835.4	$	817.7

Unamortized debt issuance costs presented above are included as a deduction from the carrying amount of long-term debt.

Credit Facility

We have a credit agreement (the Credit Facility) with a consortium of banks. The Credit Facility provides for an $800.0 million revolving credit facility, a $50.0 million swingline facility and provides for the ability to incur one or more uncommitted incremental revolving or term loan facilities in an aggregate amount of at least $730.0 million, subject to applicable financial covenants. The interest rate on the Credit Facility is variable and may be based on the Secured Overnight Financing Rate (SOFR), which is the applicable benchmark for current borrowings, or an alternative benchmark depending on the borrowing type.

Borrowings under the Credit Facility are secured by a first priority lien on substantially all of the assets (excluding real property and other customary assets) of Koppers Inc., Koppers Holdings Inc. and our material domestic subsidiaries. The Credit Facility contains certain covenants that may limit Koppers Inc. and its restricted subsidiaries from taking certain actions. These limitations include, among others, restrictions on additional indebtedness, liens, dividends, investments, acquisitions, certain distributions, asset sales, transactions with affiliates and modifications to material documents, including organizational documents. In addition, such covenants may give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios.

As of December 31, 2023, we had $330.0 million of unused revolving credit availability for working capital purposes after restrictions from certain letter of credit commitments and other covenants. As of December 31, 2023, $8.6 million of commitments were utilized by outstanding letters of credit. For the years ended December 31, 2023, 2022 and 2021, we incurred commitment fees of approximately 22, 22 and 25 basis points, respectively, on the undrawn portion of our credit facility to maintain credit availability.

Term Loan B

On April 10, 2023, we entered into Amendment No. 1 to the Credit Facility (Amendment No. 1), and on October 11, 2023, we entered into Amendment No. 2 to the Credit Facility (Amendment No. 2). Amendment No. 1 added a new class of senior secured term loans under the Credit Facility in an aggregate principal amount of $400.0 million (the Term Loan B), among other modifications. The Term Loan B was issued at 97 percent of face value, resulting in $388.0 million of net proceeds, before debt financing costs. The interest rate on the Term Loan B is variable and is based on, at our option, adjusted Term SOFR Rate or adjusted Daily Simple SOFR. Under Amendment No. 2, the interest rate margins applicable to adjusted Term SOFR Rate or adjusted Daily Simple SOFR loans are 3.50 percent with a floor of 0.50 percent.

Under Amendment No. 2, the principal balance of the Term Loan B is repayable in quarterly installments in an amount equal to 0.25 percent of the principal amount, commencing on January 1, 2024 and on the last business day of each quarterly period thereafter, with the balance due at maturity on April 10, 2030.

Interest Rate Swaps

See Note 5 – Derivative Financial Instruments for discussion of the interest rate swap agreements, which effectively convert the variable rate to a fixed rate for a portion of our variable rate debt.

Senior Notes due 2025

Koppers Inc.’s $500 million Senior Notes due 2025 (the 2025 Notes) were unsecured senior obligations of Koppers Inc. and were guaranteed by Koppers Holdings Inc. and certain of Koppers Inc.’s domestic subsidiaries.

On April 11, 2023, we used the proceeds from the Term Loan B, cash on hand and available borrowing capacity under our existing Credit Facility to redeem all of the outstanding 2025 Notes at face value and to pay any fees and expenses incurred in connection with the issuance of the Term Loan B and the redemption of the 2025 Notes.

Debt Maturities

At December 31, 2023, the aggregate debt maturities for the next five years are as follows:


(Dollars in millions)
2024	$	5.0
2025		4.0
2026		4.0
2027		465.4
2028		4.0
Thereafter		378.0
Total principal debt		860.4
Less unamortized discount		11.0
Total debt	$	849.4

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//470/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

+ Details

Consolidated Statement of Shareholders' Equity - USD ($) $ in Millions	Total	Preferred Stock [Member] Senior Convertible Preferred Stock [Member]	Common Stock [Member]	Noncontrolling Interests [Member]	Retained Earnings (Accumulated Deficit) [Member]	Currency Translation Adjustment [Member]	Unrecognized Gains (Losses) on Cash Flow Hedges [Member]	Unrecognized Pension Prior Service Cost [Member]	Unrecognized Pension Net Loss [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Koppers Shareholder's Equity (Deficit) [Member]
Balance at Dec. 31, 2020		$ 0.0	$ 0.2	$ 4.3	$ 215.8	$ (18.1)	$ 44.4	$ (0.6)	$ (41.6)	$ 234.1	$ (92.5)
Net income (loss) attributable to noncontrolling interests	$ (0.3)			(0.3)
Net Income (Loss)	85.2				85.2
Common Stock dividends ($0.24 and $0.20 per share)					0.0
Purchases											(11.6)
Loss on sale of subsidiary						(4.4)
Change in currency translation adjustment	(16.4)			0.2		(12.2)
Reclassification of unrealized gains on cash flow hedges to expense, net of tax expense of $0.5, $13.4 and $7.2							(22.8)
Change in cash flow hedges, net of tax benefit (expense) of $0.3, $(0.6) and $(6.7)							19.0
Revaluation of unrecognized prior service benefit,net of tax benefit of $0.0, $0.0 and $0.0								0.1
Reclassification of unrecognized pension net loss to expense, net of tax benefit of $0.4, $0.4 and $0.3									1.1
Revaluation of unrecognized pension net (loss) gain, net of tax (benefit) expense of $0.7, $0.1 and $(1.6)									(4.9)
Employee stock plans										13.0
Issuance of common stock			0.0							2.4
Balance at Dec. 31, 2021	410.8	0.0	0.2	4.2	301.0	(34.7)	40.6	(0.5)	(45.4)	249.5	(104.1)	$ (40.0)	$ 406.6
Net income (loss) attributable to noncontrolling interests	(0.2)			(0.2)
Net Income (Loss)	63.4				63.4
Common Stock dividends ($0.24 and $0.20 per share)					(4.2)
Purchases											(23.5)
Loss on sale of subsidiary						0.0
Change in currency translation adjustment	(21.6)			(0.4)		(21.2)
Reclassification of unrealized gains on cash flow hedges to expense, net of tax expense of $0.5, $13.4 and $7.2							(40.4)
Change in cash flow hedges, net of tax benefit (expense) of $0.3, $(0.6) and $(6.7)							1.6
Revaluation of unrecognized prior service benefit,net of tax benefit of $0.0, $0.0 and $0.0								0.0
Reclassification of unrecognized pension net loss to expense, net of tax benefit of $0.4, $0.4 and $0.3									1.3
Revaluation of unrecognized pension net (loss) gain, net of tax (benefit) expense of $0.7, $0.1 and $(1.6)									1.4
Employee stock plans										13.2
Issuance of common stock			0.0							1.2
Balance at Dec. 31, 2022	403.0	$ 0.0	0.2	3.6	360.2	(55.9)	1.8	(0.5)	(42.7)	263.9	(127.6)	(97.3)	399.4
Net income (loss) attributable to noncontrolling interests	0.6			0.6
Net Income (Loss)	89.2				89.2
Common Stock dividends ($0.24 and $0.20 per share)					(5.4)
Purchases											(20.1)
Loss on sale of subsidiary						0.0
Change in currency translation adjustment	6.9			(0.1)		7.0
Reclassification of unrealized gains on cash flow hedges to expense, net of tax expense of $0.5, $13.4 and $7.2							(1.5)
Change in cash flow hedges, net of tax benefit (expense) of $0.3, $(0.6) and $(6.7)							(1.2)
Revaluation of unrecognized prior service benefit,net of tax benefit of $0.0, $0.0 and $0.0								0.0
Reclassification of unrecognized pension net loss to expense, net of tax benefit of $0.4, $0.4 and $0.3									1.2
Revaluation of unrecognized pension net (loss) gain, net of tax (benefit) expense of $0.7, $0.1 and $(1.6)									3.0
Employee stock plans										17.3
Issuance of common stock			0.1							9.9
Balance at Dec. 31, 2023	$ 503.0		$ 0.3	$ 4.1	$ 444.0	$ (48.9)	$ (0.9)	$ (0.5)	$ (38.5)	$ 291.1	$ (147.7)	$ (88.8)	$ 498.9

Consolidated Statement of Comprehensive (Loss) Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Tax benefit, unrealized loss on cash flow hedges	$ 0.8	$ 14.0	$ 0.5
Unrecognized pension prior service cost, tax benefit	0.0	0.0	0.0
Tax (expense) benefit, unrecognized pension net income	$ (1.1)	$ (0.5)	$ 1.3

Income Taxes - Summary of Valuation Allowances Recorded to Offset Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Income Taxes [Line Items]
Total valuation allowances	$ 43.1	$ 43.8
Foreign [Member] \| Tax Credits [Member]
Income Taxes [Line Items]
Total valuation allowances	15.2	16.1
Foreign [Member] \| Operating Losses and Capital Losses [Member]
Income Taxes [Line Items]
Total valuation allowances	8.6	8.3
State [Member] \| Operating Losses and Tax Credits [Member]
Income Taxes [Line Items]
Total valuation allowances	$ 19.3	$ 19.4

Commitments and Contingent Liabilities

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingent Liabilities

17. Commitments and Contingent Liabilities

We are involved in litigation and various proceedings relating to environmental laws and regulations, product liability and other matters. Certain of these matters are discussed below. The ultimate resolution of these contingencies is subject to significant uncertainty and should we fail to prevail in any of these legal matters or should several of these legal matters be resolved against us in the same reporting period, these legal matters could, individually or in the aggregate, be material to the consolidated financial statements.

Legal Proceedings

Coal Tar Pitch Cases. Koppers Inc. is one of several defendants in lawsuits filed in two states in which the plaintiffs claim they suffered a variety of illnesses (including cancer) as a result of exposure to coal tar pitch sold by the defendants. There were 51 plaintiffs in 27 cases pending as of December 31, 2023, which is unchanged from December 31, 2022. As of December 31, 2023, there were 26 cases pending in the Court of Common Pleas of Allegheny County, Pennsylvania, and one case pending in the Circuit Court of Knox County, Tennessee.

The plaintiffs in all 27 pending cases seek to recover compensatory damages. Plaintiffs in 24 of those cases also seek to recover punitive damages. The plaintiffs in the 26 cases filed in Pennsylvania seek unspecified damages in excess of the court’s minimum jurisdictional limit. The plaintiff in the Tennessee state court case seeks damages of $15.0 million. The other defendants in these lawsuits vary from case to case and include companies such as Beazer East, Inc. (Beazer East), Honeywell International Inc., Graftech International Holdings, UCAR Carbon Company, Inc., and SGL Carbon Corporation. Discovery is proceeding in these cases. No trial dates have been set in any of these cases.

We have not provided a reserve for the coal tar pitch lawsuits because, at this time, we cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. The timing of resolution of these cases cannot be reasonably determined. Although Koppers Inc. is vigorously defending these cases, an unfavorable resolution of these matters may have a material adverse effect on our business, financial condition, cash flows and results of operations.

Environmental and Other Litigation Matters

We are subject to federal, state, local and foreign laws and regulations and potential liabilities relating to the protection of the environment and human health and safety including, among other things, the cleanup of contaminated sites, the treatment, storage and disposal of wastes, the discharge of effluent into waterways, the emission of substances into the air and various health and safety matters. We expect to incur substantial costs for ongoing compliance with such laws and regulations. We may also face governmental or third-party claims, or otherwise incur costs, relating to cleanup of, or for injuries resulting from, contamination at sites associated with past and present operations. We accrue for environmental liabilities when a determination can be made that a liability is probable and reasonably estimable.

Environmental and Other Liabilities Retained or Assumed by Others. We have agreements with former owners of certain of our operating locations under which the former owners retained, assumed and/or agreed to indemnify us against certain environmental and other liabilities. The most significant of these agreements was entered into at Koppers Inc.’s formation on December 29, 1988 (the Acquisition). Under the related asset purchase agreement between Koppers Inc. and Beazer East, subject to certain limitations, Beazer East retained the responsibility for and agreed to indemnify Koppers Inc. against certain liabilities, damages, losses and costs, including, with certain limited exceptions, liabilities under and costs to comply with environmental laws to the extent attributable to acts or omissions occurring prior to the Acquisition and liabilities related to products sold by Beazer East prior to the Acquisition (the Indemnity). Beazer Limited, the parent company of Beazer East, unconditionally guaranteed Beazer East’s performance of the Indemnity pursuant to a guarantee.

The Indemnity provides different mechanisms, subject to certain limitations, by which Beazer East is obligated to indemnify Koppers Inc. with regard to certain environmental, product and other liabilities and imposes certain conditions on Koppers Inc. before receiving such indemnification, including, in some cases, certain limitations regarding the time period as to which claims for indemnification can be brought. In July 2004, Koppers Inc. and Beazer East agreed to amend the environmental indemnification provisions of the December 29, 1988 asset purchase agreement to extend the indemnification period for pre-closing environmental liabilities, subject to the following paragraph, and agreed to share toxic tort litigation defense arising from any sites acquired from Beazer East.

Qualified expenditures under the Indemnity are not subject to a monetary limit. Qualified expenditures under the Indemnity include (i) environmental cleanup liabilities required by third parties, such as investigation, remediation and closure costs, relating to pre-December 29, 1988 (Pre-Closing) acts or omissions of Beazer East or its predecessors; (ii) environmental claims by third parties for personal injuries, property damages and natural resources damages relating to Pre-Closing acts or omissions of Beazer East or its predecessors; (iii) punitive damages for the acts or omissions of Beazer East and its predecessors without regard to the date of the alleged conduct and (iv) product liability claims for products sold by Beazer East or its predecessors without regard to the date of the alleged conduct. The indemnification period ended July 14, 2019 (the Claim Deadline), and Beazer East may now tender certain third-party claims described in sections (i) and (ii) above to Koppers Inc. However, to the extent the third-party claims described in sections (i) and (ii) above were tendered to Beazer East by the Claim Deadline, Beazer East will continue to be required to pay the costs arising from such claims under the Indemnity. Furthermore, the Claim Deadline did not change the provisions of the Indemnity with respect to indemnification for non-environmental claims, such as product liability claims, which claims may continue to be tendered by Koppers Inc. to Beazer East.

The Indemnity provides for the resolution of issues between Koppers Inc. and Beazer East by an arbitrator on an expedited basis upon the request of either party. The arbitrator could be asked, among other things, to make a determination regarding the allocation of environmental responsibilities between Koppers Inc. and Beazer East. Arbitration decisions under the Indemnity are final and binding on the parties.

Contamination has been identified at most manufacturing and other sites of our subsidiaries. One site currently owned and operated by Koppers Inc. in the United States is listed on the National Priorities List promulgated under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, as amended (CERCLA). Currently, at the properties acquired from Beazer East, which includes the National Priorities List site and all but one of the sites permitted under the Resource Conservation and Recovery Act (RCRA), a significant portion of all investigative, cleanup and closure activities are being conducted and paid for by Beazer East pursuant to the terms of the Indemnity. In addition, other of Koppers Inc.’s sites are or have been operated under RCRA and various other environmental permits, and remedial and closure activities are being conducted at some of these sites.

To date, the parties that retained, assumed and/or agreed to indemnify us against the liabilities referred to above, including Beazer East, have performed their obligations in all material respects. Periodically, issues have arisen between Koppers Inc. and Beazer East and/or other indemnitors that have been resolved without arbitration. Koppers Inc. and Beazer East engage in discussions from time to time that involve, among other things, the allocation of environmental costs related to certain operating and closed facilities.

If for any reason (including disputed coverage or financial incapability) one or more of such parties fail to perform their obligations and we are held liable for or otherwise required to pay all or part of such liabilities without reimbursement, the imposition of such liabilities on us could have a material adverse effect on our business, financial condition, cash flows and results of operations. Furthermore, we could be required to record a contingent liability on our balance sheet with respect to such matters, which could result in a negative impact to our business, financial condition, cash flows and results of operations.

Domestic Environmental Matters. Koppers Inc. has been named as one of the potentially responsible parties (PRPs) at the Portland Harbor CERCLA site located on the Willamette River in Oregon. Koppers Inc. operated a coal tar pitch terminal near the site. Koppers Inc. has responded to an EPA information request and has executed a PRP agreement which outlines a private process to develop an allocation of past and future costs among more than 80 parties to the site. Koppers Inc. believes it is a de minimis contributor at the site.

The EPA issued its Record of Decision (ROD) in January 2017 for the Portland Harbor CERCLA site. The selected remedy includes a combination of sediment removal, capping, enhanced and monitored natural recovery and riverbank improvements. The ROD does not determine who is responsible for remediation costs. At that time, the net present value and undiscounted costs of the selected remedy as estimated in the ROD are approximately $1.1 billion and $1.7 billion, respectively. These costs will likely increase given the remedy will not be implemented for several years. Responsibility for implementing and funding that work will be decided in the separate private allocation process which is ongoing.

Additionally, Koppers Inc. is involved in two separate matters involving natural resource damages at the Portland Harbor site. One matter involves claims by the trustees to recover damages based upon an assessment of damages to natural resources caused by the releases of hazardous substances to the Willamette River. The assessment serves as the foundation to estimate liabilities for settlements of natural resource damages claims or litigation to recover from those who do not settle with the trustee groups. Koppers Inc. has been engaged in a process to resolve its natural resource damage liabilities for the assessment area. A second matter involves a lawsuit filed in January 2017 by the Yakama Nation in Oregon federal court. Yakama Nation seeks recovery for response costs and the costs of assessing injury to natural resources to waterways beyond the current assessment area. Following the most recent court rulings, the Yakama Nation case has been stayed pending completion of the private allocation process for the Portland Harbor CERCLA site.

In September 2009, Koppers Inc. received a general notice letter notifying it that it may be a PRP at the Newark Bay CERCLA site. In January 2010, Koppers Inc. submitted a response to the general notice letter asserting that Koppers Inc. is a de minimis party at this site.

We have accrued the estimated costs of participating in the PRP group at the Portland Harbor and Newark Bay CERCLA sites and estimated de minimis contributor settlement amounts at the sites totaling $3.9 million as of December 31, 2023. The actual cost could be materially higher as there has not been a determination of how those costs will be allocated among the PRPs at the sites. Accordingly, an unfavorable resolution of these matters may have a material adverse effect on our business, financial condition, cash flows and results of operations.

There are two plant sites related to the Performance Chemicals business and one plant site related to the Utility and Industrial Products business in the United States where we have recorded environmental remediation liabilities for soil and groundwater contamination that occurred prior to our acquisition of the businesses. As of December 31, 2023, our estimated environmental remediation liability for these sites totals $3.8 million.

Foreign Environmental Matters. There is one plant site related to the Performance Chemicals business located in Australia where we have recorded an environmental remediation liability for soil and groundwater contamination which occurred prior to the acquisition of the business. As of December 31, 2023, our estimated environmental remediation liability for the acquired site totals $1.3 million.

Environmental Reserves Rollforward. The following table reflects changes in the accrual for environmental remediation. A total of $2.2 million and $2.5 million are classified as current liabilities as of December 31, 2023 and December 31, 2022, respectively:


	December 31,
	2023			2022
(Dollars in millions)
Balance at beginning of year	$	10.9		$	10.7
Expense		0.2			1.6
Cash expenditures		(0.4	)		(1.1	)
Currency translation		(0.1	)		(0.3	)
Balance at end of year	$	10.6		$	10.9

Consolidated Statement of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Common Stock dividends	$ 0.24	$ 0.20
Unrealized gains on cash flow hedges to expense, tax expense	$ (0.8)	$ (14.0)	$ (0.5)
Revaluation of unrecognized pension net (loss) gain, tax (benefit) expense	0.7	0.1	(1.6)
Unrecognized Gains (Losses) on Cash Flow Hedges [Member]
Unrealized gains on cash flow hedges to expense, tax expense	0.5	13.4	7.2
Deferred losses on cash flow hedges, tax benefit (expense)	0.3	(0.6)	(6.7)
Unrecognized Pension Prior Service Cost [Member]
Revaluation of unrecognized prior service benefit, tax benefit	0.0	0.0	0.0
Unrecognized Pension Net Loss [Member]
Reclassification of unrecognized pension net loss, tax benefit	$ 0.4	$ 0.4	$ 0.3

Earnings and Dividends per Common Share - Additional Information (Detail) - $ / shares		12 Months Ended
	Feb. 14, 2024	Dec. 31, 2023	Dec. 31, 2022
Dividends Payable [Line Items]
Quarterly dividend declared per common share		$ 0.24	$ 0.20
Subsequent Event [Member]
Dividends Payable [Line Items]
Quarterly dividend, declared date	Feb. 14, 2024
Quarterly dividend declared per common share	$ 0.07
Quarterly dividend, payable date	Mar. 25, 2024
Quarterly dividend, payable date of record	Mar. 08, 2024

Common Stock and Senior Convertible Preferred Stock

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Common Stock And Senior Convertible Preferred Stock

4. Common Stock and Senior Convertible Preferred Stock

There was no senior convertible preferred stock issued or outstanding for the periods presented. The following table presents the changes in common stock and treasury stock:


	December 31,
	2023			2022			2021
(Shares in thousands)
Common Stock Issued:
Balance at beginning of year		24,547			24,027			23,688
Issued for employee stock plans		616			520			339
Balance at end of year		25,163			24,547			24,027
Treasury Stock:
Balance at beginning of year		(3,784	)		(2,931	)		(2,590	)
Shares repurchased		(519	)		(853	)		(341	)
Balance at end of year		(4,303	)		(3,784	)		(2,931	)
Common Stock Outstanding		20,860			20,763			21,096

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Pensions and Post-Retirement Benefit Plans - Schedule of Weighted Average Asset Allocation for Company's Pension Plans (Detail)	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
December 31,	100.00%	100.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
December 31,	72.00%	52.00%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
December 31,	0.00%	20.00%
Other [Member]
Defined Benefit Plan Disclosure [Line Items]
December 31,	28.00%	28.00%

Subsequent Events

12 Months Ended

Dec. 31, 2023

Subsequent Events [Abstract]

Subsequent Events

18. Subsequent Events

On February 27, 2024, we signed an agreement to acquire substantially all of the assets of Brown Wood Preserving Company, Inc. and certain of its affiliates (Brown Wood) for approximately $100 million in cash. Brown Wood is a utility pole treating business with principal operating locations in Alabama and Mississippi. We plan to finance the purchase with cash and available borrowings under our Credit Facility. The parties expect the transaction to close in the second quarter of 2024, subject to satisfaction of customary closing conditions.

Segment Information - Schedule of Revenues and Long-Lived Assets by Geographic Area (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	$ 2,154.2	$ 1,980.5	$ 1,678.6
Long-lived assets	1,126.1	1,062.9	1,018.8
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	1,468.1	1,271.1	1,134.2
Long-lived assets	942.3	902.9	857.3
Australia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	265.0	283.0	230.6
Long-lived assets	75.6	73.8	78.9
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	213.3	248.9	195.8
Long-lived assets	91.0	67.6	63.3
Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	207.8	177.5	118.0
Long-lived assets	$ 17.2	$ 18.6	$ 19.3

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 924
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
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+ Details

Derivative Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2023

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of Fair Value of Outstanding Derivative contracts

The fair value of the outstanding derivative contracts recorded in the balance sheet are as follows:


	December 31, 2023
	Heating Oil Contracts			Interest Rate Swap Contracts			Copper Swap Contracts		Foreign Currency Forward Contracts			Total
(Dollars in millions)
Derivative contracts	$	0.0		$	2.8		$	4.1	$	0.2		$	7.1
Accrued liabilities		(0.3	)		0.0			0.0		(0.1	)		(0.4	)
Other long-term liabilities		0.0			(6.5	)		0.0		0.0			(6.5	)
Net asset (liability) on balance sheet	$	(0.3	)	$	(3.7	)	$	4.1	$	0.1		$	0.2
Accumulated other comprehensive (loss) gain, net of tax	$	0.0		$	(2.9	)	$	2.0	$	0.0		$	(0.9	)


	December 31, 2022
		Copper Swap Contracts			Foreign Currency Forward Contracts			Total
(Dollars in millions)
Derivative contracts		$	3.0		$	0.1		$	3.1
Other assets			0.4			0.0			0.4
Accrued liabilities			(0.3	)		(0.1	)		(0.4	)
Net asset on balance sheet		$	3.1		$	0.0		$	3.1
Accumulated other comprehensive gain, net of tax		$	1.8		$	0.0		$	1.8

Schedule of Outstanding Copper Swap Contracts

As of the periods presented, we had outstanding copper swap contracts of the following amounts:


	Units Outstanding (in Pounds)				Net Fair Value - Asset
	December 31,				December 31,
	2023		2022		2023		2022
(Amounts in millions)
Cash flow hedges		31.7		21.3	$	2.6	$	2.5
Not designated as hedges		9.5		6.0		1.5		0.6
Total		41.2		27.3	$	4.1	$	3.1

Schedule of Unrealized Gain (Loss) from Contract Where Hedge Accounting Was Not Elected

The unrealized gain (loss) from copper swap contracts where hedge accounting was not elected is as follows:


	Year Ended December 31,
	2023		2022			2021
(Dollars in millions)
Gain (loss) from contracts where hedge accounting was not elected	$	0.9	$	(6.5	)	$	(3.8	)

Summary of Net Currency Units Outstanding

The net currency units outstanding for contracts were:


	December 31,
	2023		2022
(In millions)
Australian Dollars		AUD 3.0		AUD 3.0
United States Dollars		USD 10.3		USD 9.3

Income Taxes - Summary of Income Taxes Reconciled with Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Federal income tax rate	21.00%	21.00%	21.00%
Foreign earnings taxed at different rates	4.90%	8.70%	4.30%
State income taxes, net of federal tax benefit	1.40%	(0.20%)	2.10%
GILTI inclusion, net of foreign tax credits	0.20%	1.70%	0.20%
Change in tax contingency reserves	0.20%	(0.10%)	(1.10%)
Valuation allowance adjustments	0.00%	0.90%	1.90%
Deferred tax adjustments	0.00%	0.00%	(0.20%)
Other	0.20%	1.10%	0.60%
Total effective tax rate	27.90%	33.10%	28.80%

Commitments and Contingent Liabilities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2023 USD ($) Case Site Plant State Plaintiff Party	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Loss Contingencies [Line Items]
Number of states with new claims filed \| State	2
Number of plaintiffs \| Plaintiff	51
Environmental remediation and regulation liability	$ 10,600,000	$ 10,900,000	$ 10,700,000
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Liabilities, Current
Accrued liability for environmental matters, current	$ 2,200,000	$ 2,500,000
Environmental Loss Contingency, Current, Statement of Financial Position [Extensible Enumeration]	Liabilities, Current	Liabilities, Current
Portland Harbor and Newark Bay CERCLA sites [Member]
Loss Contingencies [Line Items]
Costs of participating in PRP group	$ 3,900,000
Beazer East [Member]
Loss Contingencies [Line Items]
Sites listed on National Priorities List \| Site	1
Compensatory Damages [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	27
Punitive Damages [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	24
Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	27
Reserve for legal proceedings	$ 0
Pennsylvania [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	26
Pennsylvania [Member] \| Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	26
Sweetwater, Tennessee [Member] \| Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	1
Compensatory damages	$ 15,000,000
Oregon [Member]
Loss Contingencies [Line Items]
Number of potential responsible parties \| Party	80
Net present value of selected remedy estimation	$ 1,100,000,000
Undiscounted cost of selected remedy estimation	1,700,000,000
United States [Member]
Loss Contingencies [Line Items]
Environmental remediation and regulation liability	$ 3,800,000
United States [Member] \| Utility and Industrial Products [Member]
Loss Contingencies [Line Items]
Number of plant sites \| Plant	1
United States [Member] \| Performance Chemicals [Member]
Loss Contingencies [Line Items]
Number of plant sites \| Plant	2
Australia [Member] \| Performance Chemicals [Member]
Loss Contingencies [Line Items]
Environmental remediation and regulation liability	$ 1,300,000

Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 3.5	$ 3.3	$ 2.6
Increase (Decrease) to Expense	3.2	0.3	1.2
Net Write-Offs	(0.2)	(0.1)	(0.5)
Currency Translation	0.0	0.0	0.0
Balance at End of Year	6.5	3.5	3.3
Deferred Tax Valuation Allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	43.8	44.5	44.6
Increase (Decrease) to Expense	0.3	0.9	3.6
Net Write-Offs	(1.1)	(0.9)	(3.6)
Currency Translation	0.1	(0.7)	(0.1)
Balance at End of Year	$ 43.1	$ 43.8	$ 44.5

Earnings and Dividends per Common Share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Earnings and Dividends per Common Share

7. Earnings and Dividends per Common Share

The computation of basic earnings per common share for the periods presented is based upon the weighted average number of common shares outstanding during the periods. The computation of diluted earnings per common share includes the effect of non-vested nonqualified stock options and stock units assuming such options and stock units were outstanding common shares at the beginning of the period. The effect of antidilutive securities is excluded from the computation of diluted loss per common share, if any.

The following table sets forth the computation of basic and diluted earnings per common share:


	Year Ended December 31,
	2023		2022			2021
(Dollars in millions, except share amounts, in thousands, and per share amounts)
Net income attributable to Koppers	$	89.2	$	63.4		$	85.2
Loss on sale of discontinued operations		0.0		(0.6	)		(0.2	)
Income from continuing operations attributable to Koppers	$	89.2	$	64.0		$	85.4
Weighted average common shares outstanding:
Basic		20,835		20,977			21,238
Effect of dilutive securities		704		336			687
Diluted		21,539		21,313			21,925
Earnings per common share – continuing operations:
Basic earnings per common share	$	4.28	$	3.05		$	4.02
Diluted earnings per common share		4.14		3.00			3.90
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share		315		952			436

On February 14, 2024, the board of directors declared a quarterly dividend of $0.07 per common share, payable on March 25, 2024 to shareholders of record as of March 8, 2024.

Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Leases

16. Leases

We recognize lease obligations and associated right-of-use assets for existing non-cancelable leases. We have non-cancelable operating leases primarily associated with railcars, office and manufacturing facilities, storage tanks, ships, production equipment and vehicles. Many of our leases include both lease (e.g., fixed rent) and non-lease components (e.g., maintenance and services). For certain significant asset classes such as railcars, storage tanks, ships and vehicles, we have separated the lease and non-lease components based on the estimated stand-alone price for each component. For the remaining asset classes, we have elected to account for these components as a single lease component. In addition, we exclude leases expiring within twelve months from balance sheet recognition.

Many of our leases include one or more options to renew. We evaluate renewal options at the lease commencement date and regularly thereafter to determine if we are reasonably certain to exercise the option, in which case we include the renewal period in our lease term. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on information available to determine the present value of the lease payments.

Lease expense for operating leases is recognized on a straight-line basis over the lease term. Variable lease expense is recognized in the period in which the obligation for those payments is incurred.

The following table presents operating lease costs, variable lease costs and supplemental cash flow information:


	Year Ended December 31,
	2023		2022		2021
(Dollars in millions)
Operating lease costs	$	28.7	$	29.3	$	30.2
Variable lease costs		4.0		3.3		3.3
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash outflow from operating leases	$	39.5	$	29.3	$	30.5

The following table presents information about the amount and timing of cash flows arising from our operating leases as of December 31, 2023:


(Dollars in millions)
2024	$	28.2
2025		22.8
2026		17.7
2027		14.7
2028		11.7
Thereafter		12.5
Total lease payments	$	107.6
Less: Interest		(17.3	)
Present value of lease liabilities	$	90.3

Supplemental consolidated balance sheet information related to leases is as follows:


	December 31,
	2023			2022
Weighted average remaining lease term, in years		5.0			5.6
Weighted average discount rate		6.8	%		7.2	%

Property, Plant and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 42,500,000	$ 41,200,000	$ 39,400,000
Impairment charges	$ 0	$ 0	$ 0

Stock-based Compensation - Summary of Performance Stock Units (Detail) - shares	Dec. 31, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	1,112,102	761,644
Performance Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	580,763	237,032
Minimum [Member] \| 2021 - 2023 [Member] \| Market Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	136,560
Minimum [Member] \| 2022 - 2024 [Member] \| Market Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	97,870
Minimum [Member] \| 2023 - 2025 [Member] \| Market Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	52,598
Minimum [Member] \| 2023 - 2025 [Member] \| Performance Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	0
Target Shares [Member] \| 2021 - 2023 [Member] \| Market Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	136,560
Target Shares [Member] \| 2022 - 2024 [Member] \| Market Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	149,246
Target Shares [Member] \| 2023 - 2025 [Member] \| Market Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	105,196
Target Shares [Member] \| 2023 - 2025 [Member] \| Performance Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	189,084
Maximum [Member] \| 2021 - 2023 [Member] \| Market Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	136,560
Maximum [Member] \| 2022 - 2024 [Member] \| Market Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	200,622
Maximum [Member] \| 2023 - 2025 [Member] \| Market Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	157,794
Maximum [Member] \| 2023 - 2025 [Member] \| Performance Condition Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	378,168

Property, Plant and Equipment

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

12. Property, Plant and Equipment


	December 31,
	2023		2022
(Dollars in millions)
Land	$	18.8	$	15.0
Buildings		99.1		80.3
Machinery and equipment		987.0		924.1
		1,104.9		1,019.4
Less accumulated depreciation		473.2		462.1
Property, plant and equipment, net	$	631.7	$	557.3

Depreciation expense for the years ended December 31, 2023, 2022 and 2021 amounted to $42.5 million, $41.2 million and $39.4 million, respectively.

Impairments – We did not incur impairment charges in 2023, 2022 and 2021.

Segment Information - Summary of Tangible and Intangible Assets by Segments (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 1,835.5	$ 1,711.4
Deferred taxes	57.8	47.7
Property, plant and equipment, net	631.7	557.3
Operating lease right-of-use assets	90.5	86.3
Goodwill	294.4	294.0	$ 296.0
Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	1,803.2	1,678.2
Corporate, Non-Segment [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Prepaid insurance and other assets	14.8	16.0
Property, plant and equipment, net	9.6	6.8
Operating lease right-of-use assets	7.9	10.4
Railroad and Utility Products and Services [Member] \| Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	743.7	660.8
Goodwill	120.6	120.6
Carbon Materials and Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	538.9	500.5
Performance Chemicals [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Goodwill	173.8	173.4	$ 175.1
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	520.6	516.9
Goodwill	$ 173.8	$ 173.4

Derivative Financial Instruments

12 Months Ended

Dec. 31, 2023

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Financial Instruments

5. Derivative Financial Instruments

We utilize derivative instruments to manage exposures to risks that have been identified, measured and are capable of being mitigated. The primary risks that we manage by using derivative instruments are commodity price risk associated with copper, fuel oil, foreign currency exchange risk, principally the U.S. dollar and Australian dollar, and interest rate risk associated with variable rate borrowings. Generally, we enter into master netting arrangements with the counterparties and offset net derivative positions with the same counterparties. Currently, our agreements do not require cash collateral.

The Company recognizes all derivative instruments as either assets or liabilities at fair value on the balance sheet. The derivative instruments are classified as current or noncurrent based upon the expected timing of cash flows and are subject to offset under our master netting arrangements. A derivative instrument's fair value is determined using significant other observable inputs, a Level 2 fair value measurement.

For derivative instruments that are designated and qualify as cash flow hedges, the effective portion of the gain or loss on the derivative is reported as a component of other comprehensive income and is reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative instruments representing hedge ineffectiveness are recognized in current earnings.

Swap contracts on copper are used to manage the price risk associated with forecasted purchases of materials used in our manufacturing processes. Generally, we will not hedge cash flow exposures for durations longer than 36 months and we have hedged certain volumes of copper through the end of 2024. We designate certain of our commodity swaps as cash flow hedges of forecasted purchases of commodities. For those commodity swaps where hedge accounting is not elected, the fair value of the commodity swap is recognized as an asset or liability on the consolidated balance sheet, and the related unrealized gain or loss on the derivative is reported in current earnings. These amounts are classified in cost of sales in the consolidated statement of operations.

We enter into heating oil swap contracts to manage price risk associated with fuel oil purchases for our plant operations and certain raw material requirements. The fair value associated with these swap contracts are not designated as hedges, and the related unrealized gain or loss on the derivative is reported in current earnings. These amounts are classified in cost of sales in the consolidated statement of operations. As of December 31, 2023, we had contracts totaling 1.5 million gallons with a net fair value of a liability totaling $0.3 million. There were no contracts outstanding in the prior year.

We enter into foreign currency forward contracts to manage foreign currency risk associated with our receivable and payable balances in addition to foreign-denominated sales. The fair value associated with forward contracts related to foreign currency that are not designated as hedges, and the related unrealized gain or loss on the derivative is reported in current earnings. These amounts are classified in cost of sales in the consolidated statement of operations.

We enter into interest rate swaps to effectively convert portions of our variable interest rate debt into fixed rate debt to add stability to interest expense and to manage our exposure to interest rate movements. We designate our interest rate swaps as cash flow hedges on interest payments.

See the consolidated statement of comprehensive income and consolidated statement of shareholders’ equity for amounts recorded in other comprehensive income and for amounts reclassified from accumulated other comprehensive (loss) income into net income for each of the three years ended December 31, 2023.

The fair value of the outstanding derivative contracts recorded in the balance sheet are as follows:


	December 31, 2023
	Heating Oil Contracts			Interest Rate Swap Contracts			Copper Swap Contracts		Foreign Currency Forward Contracts			Total
(Dollars in millions)
Derivative contracts	$	0.0		$	2.8		$	4.1	$	0.2		$	7.1
Accrued liabilities		(0.3	)		0.0			0.0		(0.1	)		(0.4	)
Other long-term liabilities		0.0			(6.5	)		0.0		0.0			(6.5	)
Net asset (liability) on balance sheet	$	(0.3	)	$	(3.7	)	$	4.1	$	0.1		$	0.2
Accumulated other comprehensive (loss) gain, net of tax	$	0.0		$	(2.9	)	$	2.0	$	0.0		$	(0.9	)


	December 31, 2022
		Copper Swap Contracts			Foreign Currency Forward Contracts			Total
(Dollars in millions)
Derivative contracts		$	3.0		$	0.1		$	3.1
Other assets			0.4			0.0			0.4
Accrued liabilities			(0.3	)		(0.1	)		(0.4	)
Net asset on balance sheet		$	3.1		$	0.0		$	3.1
Accumulated other comprehensive gain, net of tax		$	1.8		$	0.0		$	1.8

Over the next twelve months, we estimate unrealized gains of $2.0 million for commodity price hedging as well as unrealized gains of $2.1 million for interest rate swaps will be reclassified from accumulated other comprehensive income into earnings.

Copper Swap Contracts

As of the periods presented, we had outstanding copper swap contracts of the following amounts:


	Units Outstanding (in Pounds)				Net Fair Value - Asset
	December 31,				December 31,
	2023		2022		2023		2022
(Amounts in millions)
Cash flow hedges		31.7		21.3	$	2.6	$	2.5
Not designated as hedges		9.5		6.0		1.5		0.6
Total		41.2		27.3	$	4.1	$	3.1

The unrealized gain (loss) from copper swap contracts where hedge accounting was not elected is as follows:


	Year Ended December 31,
	2023		2022			2021
(Dollars in millions)
Gain (loss) from contracts where hedge accounting was not elected	$	0.9	$	(6.5	)	$	(3.8	)

Foreign Currency Forward Contracts

The net currency units outstanding for contracts were:


	December 31,
	2023		2022
(In millions)
Australian Dollars		AUD 3.0		AUD 3.0
United States Dollars		USD 10.3		USD 9.3

Interest Rate Swap Contracts

During the year ended December 31, 2023, we entered into interest rate swap agreements with an aggregate notional value of $400.0 million. The interest rate swaps effectively convert the variable rate component of our Credit Facility borrowings to a weighted average fixed rate of 3.97 percent for a portion of our variable rate debt. This weighted average fixed rate amount excludes the interest rate margin of 3.50 percent as of December 31, 2023. All swap agreements expire in April 2027. The interest rate swaps have been designated as cash flow hedges and involve the receipt of variable amounts from a counterparty in exchange for us making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount.

Pensions and Post-Retirement Benefit Plans - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) Plan	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of domestic non-qualified defined benefit plans \| Plan	3
Defined contribution plan expense	$ 9.7	$ 8.4	$ 9.1
Net actuarial loss	2.1
Fair value of pension plan assets	128.1	127.4
Pension settlement loss			20.0
Accumulated benefit obligation, pension plans	154.1	156.8
Expenses incurred	17.4	12.6	14.9
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	2.1	51.8
Fair value of pension plan assets	128.1	127.4	190.0
Benefit obligation	154.3	157.0	219.6
Expected contributions by employer	7.6
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	(0.7)	3.4
Fair value of pension plan assets	0.0	0.0	0.0
Benefit obligation	6.2	$ 6.0	9.8
Expected contributions by employer	0.6
US Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	40.0
Additional cash funding	25.0
United States [Member] \| Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment losses	6.7
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	34.3
Plan assets	33.7
Premium payment			$ 67.8
Annuity Insurance policy [Member] \| United Kingdom [Member] \| Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Revaluation decrease	2.3
Annuity Insurance policy [Member] \| Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 33.4
Salaried and Hourly Employees [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of domestic non-qualified defined benefit plans \| Plan	2

Inventories (Tables)

12 Months Ended

Dec. 31, 2023

Inventory Disclosure [Abstract]

Components of Inventories


	December 31,
	2023		2022
(Dollars in millions)
Raw materials	$	348.4	$	318.5
Work in process		17.9		10.2
Finished goods		139.0		130.4
		505.3		459.1
Less revaluation to LIFO		109.6		103.4
Inventories, net	$	395.7	$	355.7

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Accounts receivable, allowance	$ 6.5	$ 3.5
Senior Convertible Preferred Stock, par value	$ 0.01	$ 0.01
Senior Convertible Preferred Stock, shares authorized	10,000,000	10,000,000
Senior Convertible Preferred Stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	80,000,000	80,000,000
Common Stock, shares issued	25,163,238	24,547,000
Treasury Stock, balance at end of year	4,302,996	3,783,901

Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets
Cash and cash equivalents	$ 66.5	$ 33.3
Accounts receivable, net of allowance of $6.5 and $3.5	202.4	215.7
Inventories, net	395.7	355.7
Derivative contracts	7.1	3.1
Other current assets	27.3	29.0
Total current assets	699.0	636.8
Property, plant and equipment, net	631.7	557.3
Operating lease right-of-use assets	90.5	86.3
Goodwill	294.4	294.0
Intangible assets, net	102.2	116.1
Deferred tax assets	10.4	11.7
Other assets	7.3	9.2
Total assets	1,835.5	1,711.4
Liabilities
Accounts payable	202.9	207.4
Accrued liabilities	95.1	96.1
Current operating lease liabilities	22.9	20.5
Current maturities of long-term debt	5.0	0.0
Total current liabilities	325.9	324.0
Long-term debt	835.4	817.7
Accrued postretirement benefits	31.6	34.7
Deferred tax liabilities	25.9	21.5
Operating lease liabilities	67.4	66.3
Other long-term liabilities	46.3	44.2
Total liabilities	1,332.5	1,308.4
Commitments and contingent liabilities (Note 17)
Equity
Senior Convertible Preferred Stock, $0.01 par value per share; 10,000,000 shares authorized; no shares issued	0.0	0.0
Common Stock, $0.01 par value per share; 80,000,000 shares authorized; 25,163,238 and 24,547,000 shares issued	0.3	0.2
Additional paid-in capital	291.1	263.9
Retained earnings	444.0	360.2
Accumulated other comprehensive loss	(88.8)	(97.3)
Treasury stock, at cost, 4,302,996 and 3,783,901 shares	(147.7)	(127.6)
Total Koppers shareholders’ equity	498.9	399.4
Noncontrolling interests	4.1	3.6
Total equity	503.0	403.0
Total liabilities and equity	$ 1,835.5	$ 1,711.4

Common Stock and Senior Convertible Preferred Stock - Schedule of Changes in Common Stock and Treasury Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Equity [Abstract]
Common Stock, balance at beginning of year	24,547,000	24,027,000	23,688,000
Common Stock, issued for employee stock plans	616,000	520,000	339,000
Common Stock, balance at end of year	25,163,238	24,547,000	24,027,000
Treasury Stock, balance at beginning of year	(3,783,901)	(2,931,000)	(2,590,000)
Treasury Stock, shares repurchased	(519,000)	(853,000)	(341,000)
Treasury Stock, balance at end of year	(4,302,996)	(3,783,901)	(2,931,000)
Common Stock Outstanding	20,860,000	20,763,000	21,096,000

Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 89.8	$ 63.2	$ 84.9
Changes in other comprehensive income:
Currency translation adjustment	6.9	(21.6)	(16.4)
Unrealized loss on cash flow hedges, net of tax benefit of $0.8, $14.0 and $0.5	(2.7)	(38.8)	(3.8)
Unrecognized pension prior service cost, net of tax benefit of $0.0, $0.0 and $0.0	0.0	0.0	0.1
Unrecognized pension net gain (loss), net of tax (expense) benefit of $(1.1), $(0.5) and $1.3	4.2	2.7	(3.8)
Total comprehensive income	98.2	5.5	61.0
Comprehensive income (loss) attributable to noncontrolling interests	0.5	(0.5)	(0.2)
Comprehensive income attributable to Koppers	$ 97.7	$ 6.0	$ 61.2

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of presentation – The consolidated financial statements include our accounts and all majority-owned subsidiaries for which we are deemed to exercise control over its operations. All significant intercompany transactions have been eliminated in consolidation. Certain prior period amounts in the Notes to Consolidated Financial Statements have been reclassified to conform to the current period’s presentation.

Use of estimates – Accounting principles generally accepted in the United States require management to make estimates and judgments that affect the reported amounts of assets and liabilities and the disclosure of contingencies on the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Estimates have been prepared on the basis of the most current and best available information and actual results could differ materially from these estimates.

Revenue recognition – Revenue is recognized upon the completion of performance obligations under our contracts with customers and when control of a good or service is transferred to the customer. Substantially all of our contracts with customers are ship and invoice arrangements where revenue is recognized when we complete our performance obligations and transfer control to the customer. We also have certain arrangements where revenue is recognized under the contract where control of the goods or services had been transferred to the customer prior to shipment. Revenue recognition generally occurs at the point of shipment; however in certain circumstances, as shipping terms dictate, we transfer control, and revenue is recognized at the point of destination. To determine the transaction price at the time when revenue is recognized, we evaluate whether the price is subject to adjustments, such as for warranties, discounts or volume rebates, to determine the net consideration to which we expect to be entitled. Payment terms are typically within 45 days. Shipping and handling costs are included as a component of cost of sales.

We recognize revenue related to the procurement of certain untreated railroad crossties upon delivery to our plant and acceptance by the customer. Service revenue, consisting primarily of wood treating services, is recognized at the time the service is provided and the performance obligation is satisfied. Payment on sales of untreated railroad crossties and wood treating services are generally due within 30 days of the invoice date.

Contract Balances – The timing of revenue recognition results in both billed accounts receivable and unbilled receivables, both classified as accounts receivable, net of allowance within the consolidated balance sheet. Contract assets of $7.8 million and $8.3 million are recorded within accounts receivable, net of allowance within the consolidated balance sheet as of December 31, 2023 and December 31, 2022, respectively.

Cash and cash equivalents – Cash and cash equivalents include cash on hand and on deposit and investments with an original maturity of 90 days or less.

Accounts receivable – We maintain allowances for doubtful accounts for estimated losses resulting from the inability of customers to make required payments. In circumstances where we become aware of a specific customer’s inability to meet its financial obligations to Koppers, a specific reserve for bad debts is recorded against amounts due. If the financial condition of our customers were to deteriorate, resulting in an inability to make payments, additional allowances may be required.

Inventories – In the United States, CMC and RUPS inventories are valued at the lower of cost, utilizing the last-in, first-out (LIFO) basis, or net realizable value. Utilities and industrial products inventories are valued at the lower of cost, utilizing the moving average cost basis, or net realizable value. PC inventories and all other inventories outside of the United States are valued at the lower of cost, utilizing the first-in, first-out (FIFO) basis, and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. LIFO inventories constituted approximately 58 percent and 52 percent of the FIFO inventory value at December 31, 2023 and 2022, respectively. In 2023, 2022 and 2021, we recorded inventory write-downs of $0.6 million, $1.2 million and $0.6 million, respectively, related to the lower of cost and net realizable value for our subsidiaries that value inventory on the FIFO basis.

Property, plant and equipment – Property, plant and equipment are recorded at purchased cost and include improvements that significantly increase capacities or extend useful lives of existing plant and equipment. Depreciation expense is calculated by applying the straight-line method over estimated useful lives. Estimated useful lives for buildings generally range from ten to 20 years and depreciable lives for machinery and equipment generally range from three to 15 years. Net gains and losses related to asset disposals are recognized in earnings in the period in which the disposal occurs. Routine repairs, replacements and maintenance are expensed as incurred.

We periodically evaluate whether current facts and circumstances indicate that the carrying value of depreciable long-lived assets may not be recoverable. If an asset, or logical grouping of assets, is determined to be impaired, the asset is written down to its fair value using discounted future cash flows and, if available, quoted market prices. Refer to Note 3 – Acquisitions, Divestitures and Discontinued Operations for additional information.

Goodwill and other intangible assets – See Note 13.

Deferred income taxes – Deferred tax assets and liabilities are recognized for future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. The effect on deferred tax assets and liabilities of a change in tax laws is recognized in earnings in the period the new laws are enacted. A valuation allowance is recorded to reduce the carrying amounts of deferred tax assets unless it is more likely than not that such assets will be realized.

Leases – Lease arrangements are determined whether or not to be a lease at inception. Right-of-use (ROU) assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments. ROU lease liabilities are recognized based on the present value of the future minimum lease payments over the term of the lease as of the start date and may include consideration of certain adjustments including non-lease components. ROU assets are determined based on the determined ROU lease liability and may include the consideration of certain adjustments including initial direct costs, prepaid lease payments, lease incentives received, and non-lease components. The option to extend or terminate a lease is included in the determination of the ROU asset and lease liability only when it is reasonably certain that we will exercise that option.

Asset retirement obligations – Asset retirement obligations are initially recorded at present value and are capitalized as part of the cost of the related long-lived asset when sufficient information is available to estimate present value. The capitalized costs are subsequently charged to depreciation expense over the estimated useful life of the related long-lived asset. The present value of the obligation is determined by calculating the discounted value of expected future cash flows and accretion expense is recorded each month to ultimately increase this obligation to fair value.

We recognize asset retirement obligations for the removal and disposal of residues; dismantling of certain tanks required by governmental authorities; cleaning and dismantling costs for owned rail cars; cleaning costs for leased rail cars and barges; and site demolition, when required by governmental authorities or by contract.

The following table describes changes to our asset retirement obligation liabilities:


	December 31,
	2023			2022
(Dollars in millions)
Asset retirement obligation at beginning of year	$	15.5		$	13.2
Accretion expense		1.1			1.1
Revision in estimated cash flows		(0.8	)		2.2
Cash expenditures		(0.6	)		(1.0	)
Balance at end of year	$	15.2		$	15.5

Litigation and contingencies – Amounts associated with litigation and contingencies are accrued when management, after taking into consideration the facts and circumstances of each matter including any settlement offers, has determined that it is probable that a liability has been incurred and the amount of loss can be reasonably estimated. Legal costs for litigation are expensed as incurred with the exception of legal fees relating to the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, as amended (CERCLA), sites.

Environmental liabilities – We accrue for remediation costs and penalties when the responsibility to remediate is probable and the amount of related cost is reasonably estimable. If only a range of potential liability can be estimated and no amount within the range is more probable than another, the accrual is recorded at the low end of that range. Remediation liabilities are discounted if the amount and timing of the cash disbursements are readily determinable.

New Accounting Pronouncements

In March 2022, the Financial Accounting Standards Board (FASB) issued ASU No. 2022-01, Derivatives and Hedging (Topic 815): Fair Value Hedging—Portfolio Layer Method. This ASU amends and simplifies existing guidance in order to allow companies to more accurately present the economic effects of risk management activities in financial statements. The adoption of this ASU in the first quarter of 2023 did not have a material impact on our financial statements as we principally utilize cash flow hedges.

In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This ASU updates reportable segment disclosures by expanding the frequency and extent of segment disclosures. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023, and for interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied retrospectively to all prior periods presented in the financial statements. We are currently evaluating this ASU to determine its impact on our disclosures.

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. This ASU updates income tax disclosures by requiring annual disclosures of consistent categories and greater disaggregation of information in the rate reconciliation and income taxes paid disaggregated by jurisdiction. ASU No. 2023-09 is effective for fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied on a prospective basis. We are currently evaluating this ASU to determine its impact on our disclosures.

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

Income Tax Provision

Components of our income tax provision are as follows:


	Year Ended December 31,
	2023		2022			2021
(Dollars in millions)
Current:
Federal	$	7.3	$	0.0		$	(1.5	)
State		1.7		0.6			0.9
Foreign		20.1		28.4			18.2
Total current tax provision		29.1		29.0			17.6
Deferred:
Federal		3.1		0.2			10.6
State		0.6		(0.6	)		1.1
Foreign		2.0		3.0			5.2
Total deferred tax provision		5.7		2.6			16.9
Total income tax provision	$	34.8	$	31.6		$	34.5

Income before income taxes from foreign operations for 2023, 2022 and 2021 was $76.8 million, $106.8 million and $71.8 million, respectively.

The provision for income taxes is reconciled with the federal statutory income tax rate as follows:


	Year Ended December 31,
	2023			2022			2021
Federal income tax rate		21.0	%		21.0	%		21.0	%
Foreign earnings taxed at different rates		4.9			8.7			4.3
State income taxes, net of federal tax benefit		1.4			(0.2	)		2.1
GILTI inclusion, net of foreign tax credits		0.2			1.7			0.2
Change in tax contingency reserves		0.2			(0.1	)		(1.1	)
Valuation allowance adjustments		0.0			0.9			1.9
Deferred tax adjustments		0.0			0.0			(0.2	)
Other		0.2			1.1			0.6
		27.9	%		33.1	%		28.8	%

For each of the three years ended December 31, 2023, 2022 and 2021, we have recorded valuation allowance adjustments related to the value of certain deferred tax assets. In 2023, we recorded $0.3 million of adjustments to our valuation allowance for certain foreign and state tax deferred tax assets. In 2022, we recorded $0.9 million of adjustments to our valuation allowance for certain foreign and state tax deferred tax assets. In 2021, we recorded a $3.3 million valuation allowance against net deferred tax assets of our United Kingdom entities as a result of a recent history of pre-tax losses and the reversal of a deferred tax liability associated with a defined benefit pension plan.

Taxes Excluded from Net Income Attributable to Koppers

The amount of deferred income tax benefit (expense) included in comprehensive income but excluded from net income attributable to Koppers relates primarily to adjustments to copper and interest rate swap contracts of $0.8 million, $6.1 million and $0.5 million for the years ended December 31, 2023, 2022 and 2021, respectively.

The amount of deferred income tax benefit (expense) included in comprehensive income but excluded from net income attributable to Koppers relates to adjustments to reflect the unfunded status of employee post-retirement benefit plans of $(1.1) million, $(0.5) million and $1.3 million for the years ended December 31, 2023, 2022 and 2021, respectively.

Deferred Tax Assets and Liabilities

Deferred income taxes reflect the net tax effects of differences between the carrying amounts of assets and liabilities for financial reporting purposes and for income tax purposes.

Significant components of our deferred tax assets and liabilities are as follows:


	Year Ended December 31,
	2023			2022
(Dollars in millions)
Deferred tax assets:
Federal and state tax loss carryforwards, expiring in 2024 to 2043	$	19.2		$	22.6
Tax credits		16.9			17.4
Reserves, including insurance and environmental		10.4			9.3
Interest disallowance		10.2			6.4
Accrued employee compensation		8.1			6.5
Inventory		7.6			4.6
Foreign tax loss carryforwards		7.4			6.6
Pension and other post-retirement benefits obligations		7.2			8.2
Asset retirement obligations		5.6			5.3
Other		8.3			4.6
Valuation allowance		(43.1	)		(43.8	)
Total deferred tax assets		57.8			47.7
Deferred tax liabilities:
Tax over book depreciation and amortization		69.9			52.3
Gain on derivative contracts		0.0			0.7
Other		3.4			4.5
Total deferred tax liabilities		73.3			57.5
Net deferred tax liabilities	$	(15.5	)	$	(9.8	)

As a result of the Tax Cuts and Jobs Act of 2017 (the Tax Act) and the one-time mandatory transition tax, all previously unremitted earnings for which a U.S. deferred tax liability had not been accrued have now been subject to U.S. tax. As of December 31, 2023, there was approximately $544 million of such unremitted earnings. Substantially all unremitted earnings will remain indefinitely invested in our foreign subsidiaries for the foreseeable future unless we can remit any earnings as a dividend in a tax-free manner. In the event any earnings are remitted as a dividend with a tax cost due to currency gains or losses, state taxes, or foreign withholding taxes, we estimate that we will not incur significant additional taxes on those potential remittances.

Management evaluated the ability to realize the deferred tax assets that are related to our domestic and international operations. In assessing the need for a valuation allowance, management considered all positive and negative evidence related to the realization of our net deferred tax assets. We believe that we will be in a taxable income position in the foreseeable future and we will have sufficient taxable income to utilize deferred tax assets that do not have a valuation allowance related to our domestic and international operations.

Valuation allowances are recorded to offset the following deferred tax assets:


	December 31,
	2023		2022
(Dollars in millions)
State temporary differences, net operating losses and tax credits	$	19.3	$	19.4
Federal foreign tax credits		15.2		16.1
Foreign temporary differences, net operating losses and capital losses		8.6		8.3
Total valuation allowances	$	43.1	$	43.8

Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:


	December 31,
	2023			2022			2021
(Dollars in millions)
Balance at beginning of year	$	1.4		$	1.5		$	2.5
Additions based on tax provisions related to the current year		0.3			0.1			0.1
Reductions resulting from a lapse in the statute of limitations		(0.2	)		(0.2	)		(1.1	)
Balance at end of year	$	1.5		$	1.4		$	1.5

As of December 31, 2023 and 2022, the total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate, was approximately $1.5 million and $1.4 million, respectively. We do not anticipate significant increases or decreases to the amount of unrecognized tax benefits within the next twelve months.

We recognize interest expense and any related penalties from unrecognized tax benefits in income tax expense. For the year ended December 31, 2023, we recognized $0.2 million in interest and penalties. As of December 31, 2023 and 2022, we had accrued interest and penalties of approximately $0.5 million and $0.3 million, respectively.

Koppers Holdings and its subsidiaries file income tax returns in the U.S. federal jurisdiction, individual U.S. state jurisdictions and non-U.S. jurisdictions. With few exceptions, we are no longer subject to U.S. federal, U.S. state, or non-U.S. income tax examinations by tax authorities for years before 2017.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Stock-based Compensation - Performance Award Fair Value Assumptions (Detail)	12 Months Ended
	Dec. 31, 2023 $ / shares
January 2023 Grant [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 29.01
Expected volatility	66.30%
Risk-free interest rate	4.11%
Look-back period in years	3 years
Grant date fair value per share of stock performance award	$ 39.51
January 2022 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 32.19
Expected volatility	54.50%
Risk-free interest rate	1.52%
Grant date fair value per share of stock performance award	$ 17.58
January 2022 Grant [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 32.19
Expected volatility	66.90%
Risk-free interest rate	1.10%
Look-back period in years	3 years
Grant date fair value per share of stock performance award	$ 45.19
January 2021 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 29.84
Expected volatility	54.80%
Risk-free interest rate	0.59%
Grant date fair value per share of stock performance award	$ 15.79
January 2021 Grant [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 29.84
Expected volatility	68.70%
Risk-free interest rate	0.16%
Look-back period in years	3 years
Grant date fair value per share of stock performance award	$ 41.50
March 2020 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 19.63
Expected volatility	42.85%
Risk-free interest rate	0.87%
Grant date fair value per share of stock performance award	$ 8.42

Subsequent Events - Additional Information (Detail) $ in Millions	Feb. 27, 2024 USD ($)
Subsequent Event [Member] \| Brown Wood Preserving Company, Inc [Member]
Subsequent Event [Line Items]
Value of the assets acquired	$ 100

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2023	Jan. 31, 2024	Jun. 20, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Trading Symbol	KOP
Entity Registrant Name	KOPPERS HOLDINGS INC.
Entity Central Index Key	0001315257
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		21,027,990
Entity Public Float			$ 688.0
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock
Security Exchange Name	NYSE
Entity File Number	1-32737
Entity Incorporation, State or Country Code	PA
Entity Tax Identification Number	20-1878963
Entity Address, Address Line One	436 Seventh Avenue
Entity Address, City or Town	Pittsburgh
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15219
City Area Code	412
Local Phone Number	227-2001
Document Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction [Flag]	false
Documents Incorporated by Reference	Portions of the registrant’s definitive Proxy Statement for the 2024 Annual Meeting of Shareholders are incorporated by reference into Part III of this Annual Report on Form 10-K.
Auditor Name	KPMG LLP
Auditor Location	Pittsburgh, Pennsylvania (US Firm)
Auditor Firm ID	185

Debt - Schedule of Debt Maturities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
2024	$ 5.0
2025	4.0
2026	4.0
2027	465.4
2028	4.0
Thereafter	378.0
Total principal debt	860.4
Less unamortized discount	(11.0)
Total debt	$ 849.4	$ 825.3

Fair Value Measurements - Schedule of Company's Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value [Member]
Financial assets:
Investments and other assets	$ 1.3	$ 1.3
Financial liabilities:
Long-term debt (including current portion)	860.4	801.1
Carrying Value [Member]
Financial assets:
Investments and other assets	1.3	1.3
Financial liabilities:
Long-term debt (including current portion)	$ 849.4	$ 825.3

Stock-based Compensation - Summary of Status and Activity of Non-Vested Stock Awards (Detail)	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	761,644
Granted	505,617
Credited from dividends	10,998
Performance share adjustment	78,468
Vested	(222,250)
Forfeited	(22,375)
Non-vested, Ending Balance	1,112,102
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit \| $ / shares	$ 32.40
Granted, Weighted Average Grant Date Fair Value per Unit \| $ / shares	30.92
Credited from dividends, Weighted Average Grant Date Fair Value per Unit \| $ / shares	32.37
Performance share adjustment, Weighted Average Grant Date Fair Value per Unit \| $ / shares	42.18
Vested, Weighted Average Grant Date Fair Value per Unit \| $ / shares	26.44
Forfeited, Weighted Average Grant Date Fair Value per Unit \| $ / shares	32.00
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit \| $ / shares	$ 33.62
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	524,612
Granted	238,544
Credited from dividends	6,394
Performance share adjustment	0
Vested	(222,250)
Forfeited	(15,961)
Non-vested, Ending Balance	531,339
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	237,032
Granted	267,073
Credited from dividends	4,604
Performance share adjustment	78,468
Vested	0
Forfeited	(6,414)
Non-vested, Ending Balance	580,763

Goodwill and Other Identifiable Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2023

Goodwill and Intangible Assets Disclosure [Abstract]

Changes in Carrying Amount of Goodwill

The change in the carrying amount of goodwill attributable to each reporting unit was as follows:


	Performance Chemicals			Railroad Products and Services			Utility Products			Total
(Dollars in millions)
Balance at December 31, 2021	$	175.1		$	41.1		$	79.8		$	296.0
Currency translation		(1.7	)		(0.1	)		(0.2	)		(2.0	)
Balance at December 31, 2022	$	173.4		$	41.0		$	79.6		$	294.0
Currency translation		0.4			0.0			0.0			0.4
Balance at December 31, 2023	$	173.8		$	41.0		$	79.6		$	294.4

Schedule of Identifiable Intangible Assets

Our intangible assets are summarized below:


					December 31,
					2023						2022
	Estimated life in years		Weighted average remaining life in years		Gross Carrying Amount		Accumulated Amortization		Net		Gross Carrying Amount		Accumulated Amortization		Net
(Dollars in millions)
Customer contracts	9 to 18			8.1	$	225.4	$	125.2	$	100.2	$	224.9	$	110.5	$	114.4
Technology	4 to 12			2.6		26.4		26.1		0.3		26.4		26.0		0.4
Trademarks	4 to 18			11.2		8.2		6.5		1.7		7.7		6.5		1.2
Supply contracts		10		0.0		2.4		2.4		0.0		2.4		2.4		0.0
Non-compete agreements		12		0.8		1.6		1.6		0.0		1.6		1.5		0.1
Total				8.1	$	264.0	$	161.8	$	102.2	$	263.0	$	146.9	$	116.1

Schedule of Future Amortization Expense

Estimated amortization expense for the next five years is summarized below:


	Estimated annual amortization
(Dollars in millions)
2024	$	14.2
2025		13.7
2026		12.4
2027		12.0
2028		11.2

- Definition

Tabular disclosure of goodwill by reportable segment and in total which includes a rollforward schedule.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 350
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 24
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-URI https://asc.fasb.org//1943274/2147482548/350-20-55-24

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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
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+ Details

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Income before income taxes	$ 76.8	$ 106.8	$ 71.8
Valuation allowance	43.1	43.8
Income tax expense (benefit)	34.8	31.6	34.5
Unrealized gains on cash flow hedges to expense, tax expense	(0.8)	(14.0)	(0.5)
Deferred income tax benefit (expense) relating to unfunded status of employee post-retirement benefit plans	(1.1)	(0.5)	1.3
Unremitted earnings	544.0
Unrecognized tax benefits with impact on the effective tax rate	1.5	1.4
Interest expense (income) and related penalties	(0.2)
Accrued interest expense and penalties	0.5	0.3
Copper Swap Contracts [Member]
Income Taxes [Line Items]
Unrealized gains on cash flow hedges to expense, tax expense	0.8	6.1	0.5
Foreign and State Tax [Member]
Income Taxes [Line Items]
Valuation allowance	$ 0.3	$ 0.9
Foreign [Member] \| United Kingdom [Member]
Income Taxes [Line Items]
Valuation allowance			$ 3.3

Goodwill and Other Identifiable Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment charge	$ 0	$ 0	$ 0
Increase in carrying value of identifiable intangible assets	1,000,000
Amortization expense	$ 14,500,000	$ 14,900,000	$ 18,300,000

Schedule II - Valuation and Qualifying Accounts

12 Months Ended

Dec. 31, 2023

SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]

Schedule II - Valuation and Qualifying Accounts

SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS

For the years ended December 31, 2023, 2022 and 2021



	Balance at		Increase								Balance
	Beginning		(Decrease)		Net			Currency			at End
	of Year		to Expense		Write-offs			Translation			of Year
(Dollars in millions)
2023
Allowance for doubtful accounts	$	3.5	$	3.2	$	(0.2	)	$	0.0		$	6.5
Deferred tax valuation allowance	$	43.8	$	0.3	$	(1.1	)	$	0.1		$	43.1
2022
Allowance for doubtful accounts	$	3.3	$	0.3	$	(0.1	)	$	0.0		$	3.5
Deferred tax valuation allowance	$	44.5	$	0.9	$	(0.9	)	$	(0.7	)	$	43.8
2021
Allowance for doubtful accounts	$	2.6	$	1.2	$	(0.5	)	$	0.0		$	3.3
Deferred tax valuation allowance	$	44.6	$	3.6	$	(3.6	)	$	(0.1	)	$	44.5

Commitments and Contingent Liabilities - Changes in Accrued Liability for Environmental Matters (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Balance at beginning of year	$ 10.9	$ 10.7
Expense	0.2	1.6
Cash expenditures	(0.4)	(1.1)
Currency translation	(0.1)	(0.3)
Balance at end of period	$ 10.6	$ 10.9

Segment Information (Tables)

12 Months Ended

Dec. 31, 2023

Segment Reporting [Abstract]

Schedule of Segment Revenues for Significant Product Lines

Segment Revenues for Significant Product Lines


	Year Ended December 31,
	2023		2022		2021
(Dollars in millions)
Railroad and Utility Products and Services:
Railroad treated products	$	540.9	$	457.4	$	414.4
Utility poles		266.1		227.9		228.0
Railroad infrastructure products and services		90.9		103.0		87.5
Total Railroad and Utility Products and Services		897.9		788.3		729.9
Performance Chemicals:
Wood preservative products		647.2		561.2		489.1
Other products		24.4		18.7		14.2
Total Performance Chemicals		671.6		579.9		503.3
Carbon Materials and Chemicals:
Pitch and related products		394.4		399.6		279.3
Phthalic anhydride, naphthalene and other chemicals		112.0		148.4		110.2
Carbon black feedstock and distillates		78.3		64.3		55.9
Total Carbon Materials and Chemicals		584.7		612.3		445.4
Total	$	2,154.2	$	1,980.5	$	1,678.6
Intersegment revenues:
Performance Chemicals	$	28.9	$	22.2	$	15.9
Carbon Materials and Chemicals		87.4		74.3		75.3
Total	$	116.3	$	96.5	$	91.2

Summary of Results of Segment Operations

The following table sets forth certain sales and operating data by segment for the periods indicated:


	Year Ended December 31,
	2023			2022			2021
(Dollars in millions)
Depreciation and amortization expense:
Railroad and Utility Products and Services	$	24.6		$	22.3		$	22.3
Performance Chemicals		13.9			15.3			17.9
Carbon Materials and Chemicals		18.5			18.5			17.5
Total	$	57.0		$	56.1		$	57.7
Adjusted EBITDA:
Railroad and Utility Products and Services	$	84.0		$	53.6		$	45.4
Performance Chemicals		123.1			75.5			101.8
Carbon Materials and Chemicals		49.3			99.0			76.3
Items excluded from the determination of segment profit:
LIFO expense(1)		(6.0	)		(25.6	)		(28.2	)
Impairment, restructuring and plant closure costs		(0.1	)		(1.1	)		(4.2	)
Gain on sale of assets		1.8			2.5			31.2
Mark-to-market commodity hedging gains (losses)		0.5			(6.5	)		(3.8	)
Inventory adjustment(2)		0.0			(1.1	)		0.0
Interest expense		(71.0	)		(44.8	)		(40.5	)
Depreciation and amortization		(57.0	)		(56.1	)		(58.4	)
Income tax provision		(34.8	)		(31.6	)		(34.5	)
Discontinued operations		0.0			(0.6	)		(0.2	)
Net income	$	89.8		$	63.2		$	84.9
Capital expenditures:
Railroad and Utility Products and Services	$	49.8		$	47.2		$	62.0
Performance Chemicals		15.1			10.6			17.7
Carbon Materials and Chemicals		50.7			45.7			42.9
Corporate		4.9			1.8			2.4
Total	$	120.5		$	105.3		$	125.0

(1)

The LIFO expense adjustment removes the entire impact of LIFO and effectively reflects the results as if we were on a FIFO inventory basis.

(2)

Represents fair value step-up on inventory acquired in a business acquisition as described in Note 3 – Acquisitions, Divestitures and Discontinued Operations.

Summary of Tangible and Intangible Assets by Segments

The following table sets forth tangible and intangible assets allocated to each of our segments as of the dates indicated:


	December 31,
	2023		2022
(Dollars in millions)
Segment assets:
Railroad and Utility Products and Services	$	743.7	$	660.8
Performance Chemicals		520.6		516.9
Carbon Materials and Chemicals		538.9		500.5
Segment assets		1,803.2		1,678.2
Prepaid insurance and other assets		14.8		16.0
Property, plant and equipment, net		9.6		6.8
Operating lease right-of-use assets		7.9		10.4
Total	$	1,835.5	$	1,711.4
Goodwill:
Railroad and Utility Products and Services	$	120.6	$	120.6
Performance Chemicals		173.8		173.4
Total	$	294.4	$	294.0

Schedule of Revenues and Long-Lived Assets by Geographic Area

Revenues and Long-lived Assets by Geographic Area


	Year		Revenue		Long-lived assets
(Dollars in millions)
United States		2023	$	1,468.1	$	942.3
		2022		1,271.1		902.9
		2021		1,134.2		857.3
Australasia		2023		265.0		75.6
		2022		283.0		73.8
		2021		230.6		78.9
Europe		2023		213.3		91.0
		2022		248.9		67.6
		2021		195.8		63.3
Other countries		2023		207.8		17.2
		2022		177.5		18.6
		2021		118.0		19.3
Total		2023	$	2,154.2	$	1,126.1
		2022	$	1,980.5	$	1,062.9
		2021	$	1,678.6	$	1,018.8

Debt (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Schedule of Long-Term Debt Instruments


					December 31,
	Weighted Average Interest Rate			Maturity	2023		2022
(Dollars in millions)
Credit Facility		7.39	%	2027	$	461.4	$	325.3
Term Loan B		7.56	%	2030		388.0		0.0
Senior Notes due 2025	-			-		0.0		500.0
Total debt						849.4		825.3
Less short-term debt and current maturities of long-term debt						5.0		0.0
Less unamortized debt issuance costs						9.0		7.6
Long-term debt					$	835.4	$	817.7

Schedule of Debt Maturities

At December 31, 2023, the aggregate debt maturities for the next five years are as follows:


(Dollars in millions)
2024	$	5.0
2025		4.0
2026		4.0
2027		465.4
2028		4.0
Thereafter		378.0
Total principal debt		860.4
Less unamortized discount		11.0
Total debt	$	849.4

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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+ Details

Leases - Summary of Amount and Timing of Cash Flows From Operating Leases (Detail) $ in Millions	Dec. 31, 2023 USD ($)
Leases [Abstract]
2024	$ 28.2
2025	22.8
2026	17.7
2027	14.7
2028	11.7
Thereafter	12.5
Total lease payments	107.6
Less: Interest	(17.3)
Present value of lease liabilities	$ 90.3

Common Stock and Senior Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Schedule of Changes in Common Stock and Treasury Stock

The following table presents the changes in common stock and treasury stock:


	December 31,
	2023			2022			2021
(Shares in thousands)
Common Stock Issued:
Balance at beginning of year		24,547			24,027			23,688
Issued for employee stock plans		616			520			339
Balance at end of year		25,163			24,547			24,027
Treasury Stock:
Balance at beginning of year		(3,784	)		(2,931	)		(2,590	)
Shares repurchased		(519	)		(853	)		(341	)
Balance at end of year		(4,303	)		(3,784	)		(2,931	)
Common Stock Outstanding		20,860			20,763			21,096

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

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+ Details

Commitments and Contingent Liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Changes in Accrued Liability for Environmental Matters

The following table reflects changes in the accrual for environmental remediation. A total of $2.2 million and $2.5 million are classified as current liabilities as of December 31, 2023 and December 31, 2022, respectively:


	December 31,
	2023			2022
(Dollars in millions)
Balance at beginning of year	$	10.9		$	10.7
Expense		0.2			1.6
Cash expenditures		(0.4	)		(1.1	)
Currency translation		(0.1	)		(0.3	)
Balance at end of year	$	10.6		$	10.9

Derivative Financial Instruments - Schedule of Outstanding Copper Swap Contracts (Detail) - Copper Swap Contracts [Member] £ in Millions, $ in Millions	Dec. 31, 2023 GBP (£)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 GBP (£)	Dec. 31, 2022 USD ($)
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding \| £	£ 41.2		£ 27.3
Net Fair Value - Asset \| $		$ 4.1		$ 3.1
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding \| £	31.7		21.3
Net Fair Value - Asset \| $		2.6		2.5
Not Designated as Hedging Instrument [Member]
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding \| £	£ 9.5		£ 6.0
Net Fair Value - Asset \| $		$ 1.5		$ 0.6

- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References + Details

Fair Value Measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements

6. Fair Value Measurements

The following table presents the estimated fair values and the related carrying amounts of our financial instruments:


	December 31, 2023				December 31, 2022
	Fair Value		Carrying Value		Fair Value		Carrying Value
(Dollars in millions)
Financial assets:
Investments and other assets	$	1.3	$	1.3	$	1.3	$	1.3
Financial liabilities:
Long-term debt (including current portion)	$	860.4	$	849.4	$	801.1	$	825.3

Investments and other assets – Represents the broker-quoted cash surrender value on universal life insurance policies. This asset is classified as Level 2 in the valuation hierarchy and is measured from values received from financial institutions.

Debt – The fair value of our long-term debt is estimated based on the market prices for the same or similar issuances or on the current rates offered to us for debt of the same remaining maturities (Level 2). The fair value of our Credit Facility approximates carrying value due to the variable rate nature of this instrument.

See Note 5 - Derivative Financial Instruments, for the fair value of our derivative financial instruments.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Revenue Recognition

Contract Balances

Cash and Cash Equivalents

Cash and cash equivalents – Cash and cash equivalents include cash on hand and on deposit and investments with an original maturity of 90 days or less.

Accounts Receivable

Inventories

Property, Plant and Equipment

Goodwill and Other Intangible Assets

Goodwill and other intangible assets – See Note 13.

Deferred Income Taxes

Leases

Asset Retirement Obligations

The following table describes changes to our asset retirement obligation liabilities:


	December 31,
	2023			2022
(Dollars in millions)
Asset retirement obligation at beginning of year	$	15.5		$	13.2
Accretion expense		1.1			1.1
Revision in estimated cash flows		(0.8	)		2.2
Cash expenditures		(0.6	)		(1.0	)
Balance at end of year	$	15.2		$	15.5

Litigation and Contingencies

Environmental Liabilities

New Accounting Pronouncements

Discontinued Operations - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Aug. 31, 2022	Sep. 30, 2020
Schedule Of Equity Method Investments [Line Items]
Restricted cash held with escrow					$ 1.5
Potential customary indemnity claims issued		$ 0.9
Potential customary indemnity claims shares issued		$ 0.7
Potential customary indemnity claims settled period		2022-04
Potential customary indemnity claims tax amount	$ 0.5
Discontinued operation, gain on disposal of discontinued operation, net of tax		$ 0.0	$ (0.6)	$ (0.2)
Koppers (Jiangsu) Carbon Chemical Company Limited [Member] \| Carbon Materials and Chemicals [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage						75.00%

Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Federal and state tax loss carryforwards, expiring in 2024 to 2043	$ 19.2	$ 22.6
Tax credits	16.9	17.4
Reserves, including insurance and environmental	10.4	9.3
Interest disallowance	10.2	6.4
Accrued employee compensation	8.1	6.5
Inventory	7.6	4.6
Foreign tax loss carryforwards	7.4	6.6
Pension and other postretirement benefits obligations	7.2	8.2
Asset retirement obligations	5.6	5.3
Other	8.3	4.6
Valuation allowance	(43.1)	(43.8)
Total deferred tax assets	57.8	47.7
Deferred tax liabilities:
Tax over book depreciation and amortization	69.9	52.3
Gain on derivative contracts	0.0	0.7
Other	3.4	4.5
Total deferred tax liabilities	73.3	57.5
Net deferred tax liabilities	$ (15.5)	$ (9.8)

Acquisitions, Divestitures and Discontinued Operations

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Acquisitions, Divestitures and Discontinued Operations

3. Acquisitions, Divestitures and Discontinued Operations

Acquisitions – On October 31, 2022, we acquired substantially all of the assets of Gross & Janes Co. (Gross & Janes) for $15.5 million in cash and we accounted for the transaction as a business combination. Gross & Janes was the largest independent supplier of untreated crossties in North America, with operations in Missouri, Arkansas and Texas. The business we acquired has been integrated into our RUPS segment, and we believe the acquisition strengthened our supply chain when procuring untreated crossties for our customers. Transaction costs, revenue and profit related to the acquisition were not material for the year ended December 31, 2022.

The fair value of assets and liabilities acquired is set forth in the following table:


(Dollars in millions)
Accounts receivable	$	4.3
Inventory		7.4
Property, plant and equipment		4.5
Total assets acquired		16.2
Accounts payable and accrued liabilities		0.7
Net assets acquired	$	15.5

Divestitures – We have closed and divested certain facilities in our RUPS and CMC segments in order to concentrate our facilities in regions where we believe we hold key competitive advantages to better serve our global customers.

▪

In March 2023, we sold certain assets from our closed coal tar distillation facility located in China and recorded a gain on sale of $1.8 million.

▪

In March 2022, we sold our utility pole treating facility in Sweetwater, Tennessee and recorded a gain on sale of $2.5 million.

▪

In October 2021, we sold our closed Denver, Colorado crosstie treating facility and recorded a gain on sale of $23.4 million.

▪

In February 2021, we sold our closed Follansbee, West Virginia coal tar distillation facility, and we recorded a gain on sale of $5.7 million, consisting of $2.6 million from cash proceeds in addition to the assumption of certain liabilities by the buyer.

Discontinued Operations – On September 30, 2020, we sold KJCC which was a 75 percent-owned coal tar distillation company in our CMC segment. The sale of KJCC represented a strategic shift that had a major effect on our operations and accordingly is classified as discontinued operations in our consolidated financial statements and notes.

On December 23, 2021 and March 31, 2022, the buyers issued various claims, which, after negotiation, were settled in April 2022 for $0.9 million, of which our share was $0.7 million. These claims were paid out of amounts held in escrow, and the remaining escrow amount of $1.5 million was fully released in August 2022. In the third quarter of 2022, we recorded a charge of $0.5 million related to a tax indemnity claim from the buyers which was paid in the fourth quarter of 2022.

Segment Information - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments \| Segment	3
Net sales	$ 2,154.2	$ 1,980.5	$ 1,678.6
Non-U.S. Countries [Member]
Segment Reporting Information [Line Items]
Net sales	$ 686.1	$ 709.4	$ 544.4

- Definition

+ References

+ Details

Pensions and Post-Retirement Benefit Plans

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Pensions and Post-Retirement Benefit Plans

14. Pensions and Post-Retirement Benefit Plans

We maintain a number of defined benefit and defined contribution plans to provide retirement benefits for employees in the United States, as well as employees outside the United States. These plans are maintained and contributions are made in accordance with the Employee Retirement Income Security Act of 1974 (ERISA), local statutory law or as determined by the board of directors. The defined benefit pension plans generally provide benefits based upon years of service and compensation. Pension plans are funded except for three domestic non-qualified defined benefit pension plans for certain key executives.

In the United States, all qualified and two of the non-qualified defined benefit pension plans for salaried and hourly employees have been closed to new participants and have been frozen. Accordingly, these pension plans no longer accrue additional years of service or recognize future increases in compensation for benefit purposes.

The defined contribution plans generally provide retirement assets to employee participants based upon employer and employee contributions to the participant’s individual investment account. We also provide retiree medical insurance coverage to certain U.S. employees and a life insurance benefit to most U.S. employees. For salaried employees, the retiree medical and retiree insurance plans have been closed to new participants. Expense related to defined contribution plans totaled $9.7 million, $8.4 million and $9.1 million for the years ended December 31, 2023, 2022 and 2021, respectively.

The following table provides the components of net periodic pension costs:


	Year Ended December 31,
	Pension Benefits									Other Benefits
	2023			2022			2021			2023			2022			2021
(Dollars in millions)
Service cost	$	1.6		$	1.2		$	1.5		$	0.0		$	0.0		$	0.1
Interest cost		8.2			5.6			5.2			0.3			0.3			0.3
Expected return on plan assets		(7.0	)		(7.7	)		(7.4	)		0.0			0.0			0.0
Amortization of net loss (gain)		2.2			1.8			1.4			(0.6	)		(0.1	)		0.0
Net periodic benefit cost	$	5.0		$	0.9		$	0.7		$	(0.3	)	$	0.2		$	0.4

The following table presents the change in the funded status of the pension and post-retirement plans:


	Year Ended December 31,
	Pension Benefits						Other Benefits
	2023			2022			2023			2022
(Dollars in millions)
Change in benefit obligation:
Benefit obligation at beginning of year	$	157.0		$	219.6		$	6.0		$	9.8
Service cost		1.6			1.2			0.0			0.0
Interest cost		8.2			5.6			0.3			0.3
Actuarial (gains) losses		(2.1	)		(51.8	)		0.7			(3.4	)
Settlements		(1.1	)		(1.0	)		0.0			0.0
Currency translation		1.9			(5.8	)		0.0			0.0
Benefits paid		(11.2	)		(10.8	)		(0.8	)		(0.7	)
Benefit obligation at end of year		154.3			157.0			6.2			6.0
Change in plan assets:
Fair value of plan assets at beginning of year		127.4			190.0			0.0			0.0
Actual return on plan assets		9.2			(46.1	)		0.0			0.0
Employer contribution		1.9			0.9			0.8			0.7
Settlements		(1.1	)		(1.0	)		0.0			0.0
Currency translation		1.9			(5.6	)		0.0			0.0
Benefits paid		(11.2	)		(10.8	)		(0.8	)		(0.7	)
Fair value of plan assets at end of year		128.1			127.4			0.0			0.0
Funded status of the plan	$	(26.2	)	$	(29.6	)	$	(6.2	)	$	(6.0	)

In 2023, the net actuarial gain of $2.1 million is due principally to an update to census data and mortality projections, partially offset by the decrease of 15 basis points in the discount rate used to measure the benefit obligation as of December 31, 2023 compared to the prior year. The actual return on plan assets was positive in 2023 primarily due to investment gains of $6.7 million in the US defined benefit pension plan and the revaluation increase of $2.3 million in the bulk annuity insurance policy related to our defined benefit pension plan in the United Kingdom. As of December 31, 2023, the fair value of the bulk annuity insurance policy of $33.4 million is based on the calculated pension benefit obligation and is classified as Level 3 within the fair value hierarchy. As the calculated pension benefit obligation increased due to a decrease in the discount rate, there was a commensurate increase in the value of the bulk annuity insurance policy.

We are evaluating the termination of our US qualified pension plan and are targeting the potential completion of this effort in the fourth quarter 2024. We estimate that a termination will require additional cash funding of $25 million and will result in an estimated settlement loss of $40 million, before tax, subject to changes to certain assumptions including the discount rate.

With respect to our defined benefit pension plan in the United Kingdom, during 2021, we entered into a buy-in bulk annuity insurance policy in exchange for a premium payment of $67.8 million, which is subject to adjustment as a result of subsequent data cleansing activities. This pension plan has a benefit obligation of $34.3 million and plan assets of $33.7 million as of December 31, 2023. Under the terms of this buy-in insurance policy, the insurer is liable to pay the benefits of our defined benefit pension plan in the United Kingdom, but the plan still retains full legal responsibility to pay the benefits to the members of the plan using the insurance payments. The buy-in policy will be treated as a plan asset going forward until such time as the buy-in policy is converted to a buy-out policy, which is when individual insurance policies will be assigned to each member of the plan, and the plan will no longer have legal responsibility to pay the benefits to the members. The data cleansing effort has been substantially completed, and we expect to recognize a pre-tax pension settlement loss of approximately $20 million upon the pension obligation becoming irrevocably settled.

The timing of the conversion to a buy-out policy may be impacted by a ruling from the High Court of Justice in the United Kingdom in the case of Virgin Media Limited v NTL Pension Trustees II Limited and Others related to obtaining an actuarial confirmation for certain amendments to UK pension plans. In our case, this ruling may render invalid a plan amendment we adopted in 2003 regarding a prospective change in the pension accrual rate. This ruling is currently under appeal, and until there is clarification on what constitutes a valid actuarial confirmation, the conversion to a buy-out policy may be delayed.

Plan Data


	Year Ended December 31,
	Pension Benefits
	2023		2022
(Dollars in millions)
Pension plans with projected benefit obligations in excess of plan assets:
Benefit obligation	$	152.6	$	154.4
Fair value of plan assets		125.8		124.2
Pension plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligation	$	152.4	$	154.2
Fair value of plan assets		125.8		124.2

The measurement date for all pension and post-retirement assets and obligations is December 31 for each respective year.

The accumulated benefit obligation for all defined benefit pension plans as of December 31, 2023 and December 31, 2022 was $154.1 million and $156.8 million, respectively.

Expected Contributions for the 2024 Fiscal Year

Our expected contributions for 2024 are estimated to be $7.6 million for pension plans and $0.6 million for other benefit plans.

Projected Benefit Payments

Benefit payments for pension benefits, which are primarily funded by the pension plan assets, and other benefits, which are funded by general corporate assets, are expected to be paid as follows:


	Pension Benefits		Other Benefits
(Dollars in millions)
2024	$	11.4	$	0.5
2025		11.8		0.5
2026		11.3		0.5
2027		11.2		0.5
2028		11.5		0.5
Next five years		57.3		2.4

Weighted-Average Assumptions


	December 31,
	Pension Benefits						Other Benefits
	2023			2022			2023			2022
Discount rate		5.27	%		5.42	%		5.50	%		5.58	%
Expected return on plan assets		5.62			4.65
Rate of compensation increase		3.28			3.13
Initial medical trend rate								5.40			5.40

Basis for the Selection of the Long-Term Rate of Return on Assets

The long-term rate of return on assets assumption was determined by using the plan’s asset allocation as described in the plan’s investment policy and modeling a distribution of compound average returns over a time horizon. The model uses asset class return, variance, and correlation assumptions to produce the expected return. The return assumptions used forward-looking gross returns influenced by the current bond yields, corporate bond spreads and equity risk premiums based on current market conditions.

In general, the long-term rate of return is the sum of the portion of total assets in each asset class multiplied by the expected return for that class, adjusted for expected expenses to be paid from the assets. To develop the expected long-term rate of return on assets assumption, we considered the historical returns and the future expectations for returns for each asset class, as well as the target asset allocation of the pension portfolio.

Investment Strategy

The weighted average asset allocation for our pension plans by asset category is as follows:


	December 31,
	2023			2022
Debt securities		72	%		52	%
Equity securities		0			20
Other		28			28
		100	%		100	%

Our investment strategy for our pension plans is to maintain an adequate level of diversification, to reduce interest rate and market risk and to provide adequate liquidity to meet immediate and future benefit payment requirements. We utilize investment managers to assist in identifying and monitoring investments that meet these allocation criteria. Our overall investment strategy for the U.S. qualified pension plan is to preserve capital as we evaluate our ability to terminate this plan and annuitize and irrevocably transfer this pension liability to a third party insurance company. Accordingly, by the end of 2023, all U.S. pension assets were transferred to income-generating assets in order to reduce investment return volatility.

As previously discussed, we entered into a buy-in bulk annuity insurance policy with respect to our defined benefit plan in the United Kingdom in anticipation of irrevocably transferring this pension liability to a third party insurance company.

All assets are invested in pooled or commingled investment vehicles with the exception of the insurance annuity contract. Our interest in these investment vehicles is expressed as a unit of account with a value per unit that is the result of the accumulated values of the underlying investments. Equity securities held within these investment vehicles are typically priced on a daily basis using the closing market price from the exchange through which the security is traded. Debt securities held within these investment vehicles are typically priced on a daily basis by independent pricing services. Certain investments are valued using the net asset value (NAV) practical expedient and have not been categorized in the fair value hierarchy but are included to reconcile the fair value hierarchy to the total fair value of plan assets. The fair value of real estate investments is either priced through a listing on an exchange or is subject to periodic appraisals.

The following tables set forth by level, our pension plan assets at fair value, within the fair value hierarchy:


	December 31, 2023
	Quoted prices in active markets for identical assets (Level 1)		Significant observable inputs (Level 2)		Significant unobservable inputs (Level 3)		Total
(Dollars in millions)
U.S. equity securities	$	0.0	$	0.1	$	0.0	$	0.1
International equity securities		0.0		0.4		0.0		0.4
U.S. debt securities		0.0		0.3		0.0		0.3
International debt securities		0.0		0.8		0.0		0.8
Insurance annuity contract and other investments		0.0		0.4		33.4		33.8
Cash and cash equivalents		0.0		1.5		0.0		1.5
	$	0.0	$	3.5	$	33.4	$	36.9
Investments measured at NAV(1)								91.2
Total assets at fair value							$	128.1
(1) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets.


	December 31, 2022
	Quoted prices in active markets for identical assets (Level 1)		Significant observable inputs (Level 2)		Significant unobservable inputs (Level 3)		Total
(Dollars in millions)
U.S. equity securities	$	0.0	$	4.9	$	0.0	$	4.9
International equity securities		0.0		11.1		0.0	11.1
U.S. debt securities		0.0		39.2		0.0	39.2
International debt securities		0.0	2.6			0.0	2.6
Other investments		0.0	0.5			31.5		32.0
Cash and cash equivalents		0.0		1.6		0.0		1.6
	$	0.0	$	59.9	$	31.5	$	91.4
Investments measured at NAV(1)								36.0
Total assets at fair value							$	127.4
(1) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets.

Incentive Plan

We have short-term management incentive plans that pay cash bonuses if certain company performance goals are met. Expenses incurred for these plans were $17.4 million in 2023, $12.6 million in 2022 and $14.9 million in 2021.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480794/715-70-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Subparagraph (o)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (p)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

Derivative Financial Instruments - Schedule of Fair Value of Outstanding Derivative Contracts Recorded in Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Derivative [Line Items]
Net asset (liability) on balance sheet	$ 0.2	$ 3.1
Accumulated other comprehensive (loss) gain, net of tax	(0.9)	1.8
Heating Oil Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	(0.3)
Accumulated other comprehensive (loss) gain, net of tax	0.0
Interest Rate Swaps [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	(3.7)
Accumulated other comprehensive (loss) gain, net of tax	(2.9)
Copper Swap Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	4.1	3.1
Accumulated other comprehensive (loss) gain, net of tax	2.0	1.8
Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.1	0.0
Accumulated other comprehensive (loss) gain, net of tax	0.0	0.0
Derivative Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	7.1	3.1
Derivative Contracts [Member] \| Heating Oil Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0
Derivative Contracts [Member] \| Interest Rate Swaps [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	2.8
Derivative Contracts [Member] \| Copper Swap Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	4.1	3.0
Derivative Contracts [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.2	0.1
Other Assets [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet		0.4
Other Assets [Member] \| Copper Swap Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet		0.4
Other Assets [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet		0.0
Accrued Liabilities [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	(0.4)	(0.4)
Accrued Liabilities [Member] \| Heating Oil Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	(0.3)
Accrued Liabilities [Member] \| Interest Rate Swaps [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0
Accrued Liabilities [Member] \| Copper Swap Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0	(0.3)
Accrued Liabilities [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	(0.1)	$ (0.1)
Other Long-Term Liabilities [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	(6.5)
Other Long-Term Liabilities [Member] \| Heating Oil Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0
Other Long-Term Liabilities [Member] \| Interest Rate Swaps [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	(6.5)
Other Long-Term Liabilities [Member] \| Copper Swap Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0
Other Long-Term Liabilities [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	$ 0.0

Leases - Schedule of Supplemental Consolidated Balance Sheet Information Related to Leases (Detail)	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Weighted average remaining lease term, in years	5 years	5 years 7 months 6 days
Weighted average discount rate	6.80%	7.20%

Earnings and Dividends per Common Share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Schedule of Computation of Basic and Diluted Earnings per Common Share

The following table sets forth the computation of basic and diluted earnings per common share:


	Year Ended December 31,
	2023		2022			2021
(Dollars in millions, except share amounts, in thousands, and per share amounts)
Net income attributable to Koppers	$	89.2	$	63.4		$	85.2
Loss on sale of discontinued operations		0.0		(0.6	)		(0.2	)
Income from continuing operations attributable to Koppers	$	89.2	$	64.0		$	85.4
Weighted average common shares outstanding:
Basic		20,835		20,977			21,238
Effect of dilutive securities		704		336			687
Diluted		21,539		21,313			21,925
Earnings per common share – continuing operations:
Basic earnings per common share	$	4.28	$	3.05		$	4.02
Diluted earnings per common share		4.14		3.00			3.90
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share		315		952			436

Pensions and Post-Retirement Benefit Plans - Schedule of Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.27%	5.42%
Expected return on plan assets	5.62%	4.65%
Rate of compensation increase	3.28%	3.13%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.50%	5.58%
Initial medical trend rate	5.40%	5.40%

Pensions and Post-Retirement Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans

et periodic pension costs:


	Year Ended December 31,
	Pension Benefits									Other Benefits
	2023			2022			2021			2023			2022			2021
(Dollars in millions)
Service cost	$	1.6		$	1.2		$	1.5		$	0.0		$	0.0		$	0.1
Interest cost		8.2			5.6			5.2			0.3			0.3			0.3
Expected return on plan assets		(7.0	)		(7.7	)		(7.4	)		0.0			0.0			0.0
Amortization of net loss (gain)		2.2			1.8			1.4			(0.6	)		(0.1	)		0.0
Net periodic benefit cost	$	5.0		$	0.9		$	0.7		$	(0.3	)	$	0.2		$	0.4

Schedule of Change in Funded Status of Pension and Post-Retirement Plans

The following table presents the change in the funded status of the pension and post-retirement plans:


	Year Ended December 31,
	Pension Benefits						Other Benefits
	2023			2022			2023			2022
(Dollars in millions)
Change in benefit obligation:
Benefit obligation at beginning of year	$	157.0		$	219.6		$	6.0		$	9.8
Service cost		1.6			1.2			0.0			0.0
Interest cost		8.2			5.6			0.3			0.3
Actuarial (gains) losses		(2.1	)		(51.8	)		0.7			(3.4	)
Settlements		(1.1	)		(1.0	)		0.0			0.0
Currency translation		1.9			(5.8	)		0.0			0.0
Benefits paid		(11.2	)		(10.8	)		(0.8	)		(0.7	)
Benefit obligation at end of year		154.3			157.0			6.2			6.0
Change in plan assets:
Fair value of plan assets at beginning of year		127.4			190.0			0.0			0.0
Actual return on plan assets		9.2			(46.1	)		0.0			0.0
Employer contribution		1.9			0.9			0.8			0.7
Settlements		(1.1	)		(1.0	)		0.0			0.0
Currency translation		1.9			(5.6	)		0.0			0.0
Benefits paid		(11.2	)		(10.8	)		(0.8	)		(0.7	)
Fair value of plan assets at end of year		128.1			127.4			0.0			0.0
Funded status of the plan	$	(26.2	)	$	(29.6	)	$	(6.2	)	$	(6.0	)

Plan Data


	Year Ended December 31,
	Pension Benefits
	2023		2022
(Dollars in millions)
Pension plans with projected benefit obligations in excess of plan assets:
Benefit obligation	$	152.6	$	154.4
Fair value of plan assets		125.8		124.2
Pension plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligation	$	152.4	$	154.2
Fair value of plan assets		125.8		124.2

Schedule of Projected Benefit Payments

Benefit payments for pension benefits, which are primarily funded by the pension plan assets, and other benefits, which are funded by general corporate assets, are expected to be paid as follows:


	Pension Benefits		Other Benefits
(Dollars in millions)
2024	$	11.4	$	0.5
2025		11.8		0.5
2026		11.3		0.5
2027		11.2		0.5
2028		11.5		0.5
Next five years		57.3		2.4

Schedule of Weighted-Average Assumptions

Weighted-Average Assumptions


	December 31,
	Pension Benefits						Other Benefits
	2023			2022			2023			2022
Discount rate		5.27	%		5.42	%		5.50	%		5.58	%
Expected return on plan assets		5.62			4.65
Rate of compensation increase		3.28			3.13
Initial medical trend rate								5.40			5.40

Schedule of Weighted Average Asset Allocation for Company's Pension Plans

The weighted average asset allocation for our pension plans by asset category is as follows:


	December 31,
	2023			2022
Debt securities		72	%		52	%
Equity securities		0			20
Other		28			28
		100	%		100	%

Schedule of Pension Plan Assets at Fair Value

The following tables set forth by level, our pension plan assets at fair value, within the fair value hierarchy:


	December 31, 2023
	Quoted prices in active markets for identical assets (Level 1)		Significant observable inputs (Level 2)		Significant unobservable inputs (Level 3)		Total
(Dollars in millions)
U.S. equity securities	$	0.0	$	0.1	$	0.0	$	0.1
International equity securities		0.0		0.4		0.0		0.4
U.S. debt securities		0.0		0.3		0.0		0.3
International debt securities		0.0		0.8		0.0		0.8
Insurance annuity contract and other investments		0.0		0.4		33.4		33.8
Cash and cash equivalents		0.0		1.5		0.0		1.5
	$	0.0	$	3.5	$	33.4	$	36.9
Investments measured at NAV(1)								91.2
Total assets at fair value							$	128.1
(1) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets.


	December 31, 2022
	Quoted prices in active markets for identical assets (Level 1)		Significant observable inputs (Level 2)		Significant unobservable inputs (Level 3)		Total
(Dollars in millions)
U.S. equity securities	$	0.0	$	4.9	$	0.0	$	4.9
International equity securities		0.0		11.1		0.0	11.1
U.S. debt securities		0.0		39.2		0.0	39.2
International debt securities		0.0	2.6			0.0	2.6
Other investments		0.0	0.5			31.5		32.0
Cash and cash equivalents		0.0		1.6		0.0		1.6
	$	0.0	$	59.9	$	31.5	$	91.4
Investments measured at NAV(1)								36.0
Total assets at fair value							$	127.4
(1) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets.

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Stock Options And Performance Award Fair Value Assumptions

We calculated the fair value of stock options on the date of grant using the Black-Scholes-Merton model and the assumptions listed below:


	January 2022 Grant			January 2021 Grant			March 2020 Grant
Grant date price per share of stock option award	$	32.19		$	29.84		$	19.63
Expected life in years		6.76			6.64			6.40
Expected volatility		54.50	%		54.80	%		42.85	%
Risk-free interest rate		1.52	%		0.59	%		0.87	%
Grant date fair value per share	$	17.58		$	15.79		$	8.42

Summary of Performance Stock Units

The following table shows a summary of the performance stock units as of December 31, 2023:


Performance Period	Minimum Shares		Target Shares		Maximum Shares
Market Condition Units
2021 – 2023		136,560		136,560		136,560
2022 – 2024		97,870		149,246		200,622
2023 – 2025		52,598		105,196		157,794
Performance Condition Units
2023 – 2025		0		189,084		378,168

Summary of Status and Activity of Non-Vested Stock Awards

The following table shows a summary of the status and activity of non-vested stock awards:


	Restricted Stock Units			Performance Stock Units			Total Stock Units			Weighted Average Grant Date Fair Value per Unit
Non-vested at January 1, 2023		524,612			237,032			761,644		$	32.40
Granted		238,544			267,073			505,617		$	30.92
Credited from dividends		6,394			4,604			10,998		$	32.37
Performance share adjustment		0			78,468			78,468		$	42.18
Vested		(222,250	)		0			(222,250	)	$	26.44
Forfeited		(15,961	)		(6,414	)		(22,375	)	$	32.00
Non-vested at December 31, 2023		531,339			580,763			1,112,102		$	33.62

Summary of Status and Activity of Stock Options

The following table shows a summary of the status and activity of stock options:


	Options			Weighted Average Exercise Price per Option		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2022		1,122,136		$	27.05
Exercised		(365,237	)	$	24.11
Expired		(50,031	)	$	42.16
Outstanding at December 31, 2023		706,868		$	27.51		5.02	$	16.8
Exercisable at December 31, 2023		545,392		$	27.29		4.35	$	13.0

Schedule of Stock-based Compensation Expense Recognized

The following table presents total stock-based compensation expense recognized under our LTIP and employee stock purchase plan:


	Year Ended December 31,
	2023		2022		2021
(Dollars in millions)
Stock-based compensation expense recognized:
Selling, general and administrative expenses	$	17.3	$	13.2	$	13.0
Less related income tax benefit		4.8		4.4		3.7
Decrease in net income attributable to Koppers	$	12.5	$	8.8	$	9.3
Intrinsic value of exercised stock options	$	6.4	$	0.0	$	2.2
Cash received from the exercise of stock options	$	8.8	$	0.0	$	2.3

Performance Stock Units [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Stock Options And Performance Award Fair Value Assumptions

We calculated the fair value of the performance stock unit awards on the date of the grant using assumptions listed below:


	January 2023 Grant			January 2022 Grant			January 2021 Grant
Grant date price per share of stock performance award	$	29.01		$	32.19		$	29.84
Expected volatility		66.30	%		66.90	%		68.70	%
Risk-free interest rate		4.11	%		1.10	%		0.16	%
Look-back period in years		3.00			3.00			3.00
Grant date fair value per share	$	39.51		$	45.19		$	41.50

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Segment Information - Summary of Results of Segment Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues from external customers:
Depreciation and amortization expense	$ 57.0	$ 56.1	$ 57.7
Items excluded from the determination of segment profit:
LIFO expense	(6.0)	(25.6)	(28.2)
Impairment, restructuring and plant closure costs	(0.1)	(1.1)	(4.2)
Gain on sale of assets	1.8	2.5	31.2
Mark-to-market commodity hedging gains (losses)	0.5	(6.5)	(3.8)
Inventory adjustment	0.0	(1.1)	0.0
Interest expense	(71.0)	(44.8)	(40.5)
Depreciation and amortization	(57.0)	(56.1)	(58.4)
Income tax provision	(34.8)	(31.6)	(34.5)
Discontinued operations	0.0	(0.6)	(0.2)
Net income	89.8	63.2	84.9
Capital expenditures:	120.5	105.3	125.0
Operating Segments [Member] \| Railroad and Utility Products and Services [Member]
Revenues from external customers:
Depreciation and amortization expense	24.6	22.3	22.3
Adjusted EBITDA:
Adjusted EBITDA	84.0	53.6	45.4
Items excluded from the determination of segment profit:
Capital expenditures:	49.8	47.2	62.0
Operating Segments [Member] \| Performance Chemicals [Member]
Revenues from external customers:
Depreciation and amortization expense	13.9	15.3	17.9
Adjusted EBITDA:
Adjusted EBITDA	123.1	75.5	101.8
Items excluded from the determination of segment profit:
Capital expenditures:	15.1	10.6	17.7
Operating Segments [Member] \| Carbon Materials and Chemicals [Member]
Revenues from external customers:
Depreciation and amortization expense	18.5	18.5	17.5
Adjusted EBITDA:
Adjusted EBITDA	49.3	99.0	76.3
Items excluded from the determination of segment profit:
Capital expenditures:	50.7	45.7	42.9
Corporate, Non-Segment [Member]
Items excluded from the determination of segment profit:
Capital expenditures:	$ 4.9	$ 1.8	$ 2.4

Inventories - Components of Inventories (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Inventory Disclosure [Abstract]
Raw materials	$ 348.4	$ 318.5
Work in process	17.9	10.2
Finished goods	139.0	130.4
Inventories, gross	505.3	459.1
Less revaluation to LIFO	109.6	103.4
Inventories, net	$ 395.7	$ 355.7

Stock-based Compensation - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future compensation expense related to non-vested stock-based compensation arrangements \| $	$ 21.7
Future compensation expense, weighted-average expected period of recognition in months	21 months
2021 - 2023 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of original target share	94.70%
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	3 years
Restricted Stock Units (RSUs) [Member] \| Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	1 year
Restricted Stock Units (RSUs) [Member] \| Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	4 years
Restricted Stock Units (RSUs) [Member] \| Employee [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	2 years
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting performance stock units if minimum performance criteria are not achieved \| shares	0
Stock options, term in years	3 years
Performance Stock Units [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants	200.00%
Performance Stock Units [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants	0.00%
Employee Stock Option \| Grants in March 2015 and Thereafter [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, term in years	10 years
Employee Stock Option \| Executive Officer [Member] \| Grants in March 2015 and Thereafter [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	4 years

Description of Business

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Description of Business

1. Description of Business

Parent company of Koppers Inc. – In these financial statements, unless otherwise indicated or the context requires otherwise, when the terms Koppers, the Company, we, our or us, are used, they mean Koppers Holdings Inc. (Koppers Holdings) and its subsidiaries on a consolidated basis. The use of these terms is not intended to imply that Koppers Holdings and Koppers Inc. are not separate and distinct legal entities from each other and from their respective subsidiaries. Koppers Holdings has no direct operations and no significant assets other than the stock of Koppers Inc. It depends on the dividends from the earnings of Koppers Inc. and its subsidiaries to generate the funds necessary to meet its financial obligations. The terms of Koppers Inc.’s Credit Facility (as defined in Note 15 - Debt) prohibit Koppers Inc. from paying dividends and otherwise transferring assets except for certain limited dividends.

Business description – We are a global integrated provider of treated wood products, wood treatment chemicals and carbon compounds for use in a variety of markets including the railroad, specialty chemical, utility, residential lumber, agriculture, aluminum, steel, rubber and construction industries. Our business is operated through three business segments, Railroad and Utility Products and Services (RUPS), Performance Chemicals (PC) and Carbon Materials and Chemicals (CMC).

Our RUPS segment sells treated and untreated wood products, manufactured products and services primarily to the railroad industry and treated wood products to the utility industry. Railroad products and services include procuring and treating items such as crossties, switch ties and various types of lumber used for railroad bridges and crossings and the manufacture of rail joint bars. Utility products include transmission and distribution poles and pilings. The segment also operates a railroad services business that conducts engineering, design, repair and inspection services for railroad bridges, a business related to the recovery of used crossties and a business related to the inspection of utility poles.

Our PC segment develops, manufactures, and markets wood preservation chemicals and wood treatment technologies and services a diverse range of end-markets including infrastructure, residential and commercial construction and agriculture.

Our CMC segment is primarily a manufacturer of creosote, carbon pitch, naphthalene, phthalic anhydride and carbon black feedstock. Creosote is used in the treatment of wood and carbon black feedstock is used in the production of carbon black. Carbon pitch is used in the production of aluminum and steel in electric arc furnaces. Naphthalene is used for the production of phthalic anhydride and as a surfactant in the production of concrete. Phthalic anhydride is used in the production of plasticizers, polyester resins and alkyd paints.

Debt - Schedule of Long-Term Debt Instruments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023
Debt Instrument [Line Items]
Total debt	$ 825.3	$ 849.4
Less short-term debt and current maturities of long-term debt	0.0	5.0
Less unamortized debt issuance costs	7.6	9.0
Long-term debt	$ 817.7	$ 835.4
Term Loan B [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate		7.56%
Debt, Maturity	2030
Total debt	$ 0.0	$ 388.0
7.39 Percent Credit Facility [Member] \| Credit Facility [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate		7.39%
Debt, Maturity	2027
Total debt	$ 325.3	$ 461.4
Senior Notes due 2025 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 500.0	$ 0.0

Goodwill and Other Identifiable Intangible Assets - Schedule of Identifiable Intangible Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	8 years 1 month 6 days
Gross Carrying Amount	$ 264.0	$ 263.0
Accumulated Amortization	161.8	146.9
Net	$ 102.2	116.1
Customer Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	8 years 1 month 6 days
Gross Carrying Amount	$ 225.4	224.9
Accumulated Amortization	125.2	110.5
Net	$ 100.2	114.4
Customer Contracts [Member] \| Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	9 years
Customer Contracts [Member] \| Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	18 years
Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	2 years 7 months 6 days
Gross Carrying Amount	$ 26.4	26.4
Accumulated Amortization	26.1	26.0
Net	$ 0.3	0.4
Technology [Member] \| Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	4 years
Technology [Member] \| Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	12 years
Trademarks [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	11 years 2 months 12 days
Gross Carrying Amount	$ 8.2	7.7
Accumulated Amortization	6.5	6.5
Net	$ 1.7	1.2
Trademarks [Member] \| Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	4 years
Trademarks [Member] \| Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	18 years
Supply Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	10 years
Weighted average remaining life in years	0 years
Gross Carrying Amount	$ 2.4	2.4
Accumulated Amortization	2.4	2.4
Net	$ 0.0	0.0
Non-Compete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	12 years
Weighted average remaining life in years	9 months 18 days
Gross Carrying Amount	$ 1.6	1.6
Accumulated Amortization	1.6	1.5
Net	$ 0.0	$ 0.1

Segment Information

12 Months Ended

Dec. 31, 2023

Segment Reporting [Abstract]

Segment Information

9. Segment Information

See Note 1 - Description of Business for a discussion of our three reportable segments. Our reportable segments contain multiple aggregated business units since management believes the long-term financial performance of these business units is affected by similar economic conditions. The reportable segments are each managed separately because they manufacture and distribute distinct products with different production processes.

Our primary measure of segment profitability is adjusted earnings before interest, income taxes, depreciation, amortization and certain non-cash and/or non-recurring items that do not contribute directly to management’s evaluation of our operating results (as defined by us, adjusted EBITDA). These items include impairment, restructuring and plant closure costs, acquisition-related charges, mark-to-market commodity hedging, gain/loss on sale of assets and LIFO inventory effects. This presentation is consistent with how our chief operating decision maker evaluates the results of operations and makes strategic decisions about the business. In addition, adjusted EBITDA is the primary measure used to determine the level of achievement of management’s short-term incentive goals and related payout, as well as one of the measures used to determine performance and related payouts for certain performance share units granted to management. For these reasons, we believe that adjusted EBITDA represents the most relevant measure of segment profit and loss.

Adjusted EBITDA is reconciled to net income on a consolidated basis, the most directly comparable financial measure determined and reported in accordance with U.S. GAAP. The accounting policies of the reportable segments are the same as those described in the summary of significant accounting policies. Intersegment transactions are eliminated in consolidation.

Segment Revenues for Significant Product Lines


	Year Ended December 31,
	2023		2022		2021
(Dollars in millions)
Railroad and Utility Products and Services:
Railroad treated products	$	540.9	$	457.4	$	414.4
Utility poles		266.1		227.9		228.0
Railroad infrastructure products and services		90.9		103.0		87.5
Total Railroad and Utility Products and Services		897.9		788.3		729.9
Performance Chemicals:
Wood preservative products		647.2		561.2		489.1
Other products		24.4		18.7		14.2
Total Performance Chemicals		671.6		579.9		503.3
Carbon Materials and Chemicals:
Pitch and related products		394.4		399.6		279.3
Phthalic anhydride, naphthalene and other chemicals		112.0		148.4		110.2
Carbon black feedstock and distillates		78.3		64.3		55.9
Total Carbon Materials and Chemicals		584.7		612.3		445.4
Total	$	2,154.2	$	1,980.5	$	1,678.6
Intersegment revenues:
Performance Chemicals	$	28.9	$	22.2	$	15.9
Carbon Materials and Chemicals		87.4		74.3		75.3
Total	$	116.3	$	96.5	$	91.2

The following table sets forth tangible and intangible assets allocated to each of our segments as of the dates indicated:


	December 31,
	2023		2022
(Dollars in millions)
Segment assets:
Railroad and Utility Products and Services	$	743.7	$	660.8
Performance Chemicals		520.6		516.9
Carbon Materials and Chemicals		538.9		500.5
Segment assets		1,803.2		1,678.2
Prepaid insurance and other assets		14.8		16.0
Property, plant and equipment, net		9.6		6.8
Operating lease right-of-use assets		7.9		10.4
Total	$	1,835.5	$	1,711.4
Goodwill:
Railroad and Utility Products and Services	$	120.6	$	120.6
Performance Chemicals		173.8		173.4
Total	$	294.4	$	294.0

The following table sets forth certain sales and operating data by segment for the periods indicated:


	Year Ended December 31,
	2023			2022			2021
(Dollars in millions)
Depreciation and amortization expense:
Railroad and Utility Products and Services	$	24.6		$	22.3		$	22.3
Performance Chemicals		13.9			15.3			17.9
Carbon Materials and Chemicals		18.5			18.5			17.5
Total	$	57.0		$	56.1		$	57.7
Adjusted EBITDA:
Railroad and Utility Products and Services	$	84.0		$	53.6		$	45.4
Performance Chemicals		123.1			75.5			101.8
Carbon Materials and Chemicals		49.3			99.0			76.3
Items excluded from the determination of segment profit:
LIFO expense(1)		(6.0	)		(25.6	)		(28.2	)
Impairment, restructuring and plant closure costs		(0.1	)		(1.1	)		(4.2	)
Gain on sale of assets		1.8			2.5			31.2
Mark-to-market commodity hedging gains (losses)		0.5			(6.5	)		(3.8	)
Inventory adjustment(2)		0.0			(1.1	)		0.0
Interest expense		(71.0	)		(44.8	)		(40.5	)
Depreciation and amortization		(57.0	)		(56.1	)		(58.4	)
Income tax provision		(34.8	)		(31.6	)		(34.5	)
Discontinued operations		0.0			(0.6	)		(0.2	)
Net income	$	89.8		$	63.2		$	84.9
Capital expenditures:
Railroad and Utility Products and Services	$	49.8		$	47.2		$	62.0
Performance Chemicals		15.1			10.6			17.7
Carbon Materials and Chemicals		50.7			45.7			42.9
Corporate		4.9			1.8			2.4
Total	$	120.5		$	105.3		$	125.0

(1)

The LIFO expense adjustment removes the entire impact of LIFO and effectively reflects the results as if we were on a FIFO inventory basis.

(2)

Represents fair value step-up on inventory acquired in a business acquisition as described in Note 3 – Acquisitions, Divestitures and Discontinued Operations.

Revenues and Long-lived Assets by Geographic Area


	Year		Revenue		Long-lived assets
(Dollars in millions)
United States		2023	$	1,468.1	$	942.3
		2022		1,271.1		902.9
		2021		1,134.2		857.3
Australasia		2023		265.0		75.6
		2022		283.0		73.8
		2021		230.6		78.9
Europe		2023		213.3		91.0
		2022		248.9		67.6
		2021		195.8		63.3
Other countries		2023		207.8		17.2
		2022		177.5		18.6
		2021		118.0		19.3
Total		2023	$	2,154.2	$	1,126.1
		2022	$	1,980.5	$	1,062.9
		2021	$	1,678.6	$	1,018.8

Revenues by geographic area in the above table are attributed by the destination country of the sale. Revenues from non-U.S. countries totaled $686.1 million in 2023, $709.4 million in 2022 and $544.4 million in 2021.

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Name Accounting Standards Codification
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-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Name Accounting Standards Codification
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-Paragraph 31
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//280/tableOfContent

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Leases - Schedule of Operating Lease Costs, Variable Lease Costs and Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Operating lease costs	$ 28.7	$ 29.3	$ 30.2
Variable lease costs	4.0	3.3	3.3
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash outflow from operating leases	$ 39.5	$ 29.3	$ 30.5

Inventories

12 Months Ended

Dec. 31, 2023

Inventory Disclosure [Abstract]

Inventories

11. Inventories


	December 31,
	2023		2022
(Dollars in millions)
Raw materials	$	348.4	$	318.5
Work in process		17.9		10.2
Finished goods		139.0		130.4
		505.3		459.1
Less revaluation to LIFO		109.6		103.4
Inventories, net	$	395.7	$	355.7

Pensions and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.6	$ 1.2	$ 1.5
Interest cost	8.2	5.6	5.2
Expected return on plan assets	(7.0)	(7.7)	(7.4)
Amortization of net loss (gain)	2.2	1.8	1.4
Net periodic benefit cost	$ 5.0	$ 0.9	$ 0.7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.0	$ 0.0	$ 0.1
Interest cost	0.3	0.3	0.3
Expected return on plan assets	(0.0)	(0.0)	(0.0)
Amortization of net loss (gain)	(0.6)	(0.1)	(0.0)
Net periodic benefit cost	$ (0.3)	$ 0.2	$ 0.4
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax

Stock-based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Stock-based compensation expense recognized:
Less related income tax benefit	$ 4.8	$ 4.4	$ 3.7
Decrease in net income attributable to Koppers	12.5	8.8	9.3
Intrinsic value of exercised stock options	6.4	0.0	2.2
Cash received from the exercise of stock options	8.8	0.0	2.3
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense recognized:
Stock-based compensation expense	$ 17.3	$ 13.2	$ 13.0

Income Taxes - Summary of Income Tax Provision (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current:
Federal	$ 7.3	$ 0.0	$ (1.5)
State	1.7	0.6	0.9
Foreign	20.1	28.4	18.2
Total current tax provision	29.1	29.0	17.6
Deferred:
Federal	3.1	0.2	10.6
State	0.6	(0.6)	1.1
Foreign	2.0	3.0	5.2
Total deferred tax provision	5.7	2.6	16.9
Total income tax provision	$ 34.8	$ 31.6	$ 34.5

Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment


	December 31,
	2023		2022
(Dollars in millions)
Land	$	18.8	$	15.0
Buildings		99.1		80.3
Machinery and equipment		987.0		924.1
		1,104.9		1,019.4
Less accumulated depreciation		473.2		462.1
Property, plant and equipment, net	$	631.7	$	557.3

Depreciation expense for the years ended December 31, 2023, 2022 and 2021 amounted to $42.5 million, $41.2 million and $39.4 million, respectively.

Pay vs Performance Disclosure - USD ($) $ in Millions	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income (Loss)	$ 89.2	$ 63.4	$ 85.2

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
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+ Details

Acquisitions, Divestitures and Discontinued Operations - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended				3 Months Ended	12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Oct. 31, 2021	Feb. 28, 2021	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Oct. 31, 2022	Aug. 31, 2022	Sep. 30, 2020
Business Acquisition [Line Items]
Gain on sale						$ 1.8	$ 2.5	$ 31.2
Restricted cash held with escrow										$ 1.5
Potential customary indemnity claims issued						0.9
Potential customary indemnity claims shares issued						$ 0.7
Potential customary indemnity claims settled period						2022-04
Potential customary indemnity claims tax amount					$ 0.5
Carbon Materials and Chemicals [Member] \| Koppers (Jiangsu) Carbon Chemical Company Limited [Member]
Business Acquisition [Line Items]
Ownership percentage											75.00%
Facility [Member] \| Railroad And Utility Products And Services [Member]
Business Acquisition [Line Items]
Gain on sale			$ 23.4
China [Member] \| Coal Tar Distillation [Member]
Business Acquisition [Line Items]
Gain on sale	$ 1.8
Sweetwater, Tennessee [Member] \| Pole Treating Facility [Member]
Business Acquisition [Line Items]
Gain on sale		$ 2.5
West Virginia [Member] \| Coal Tar Distillation [Member]
Business Acquisition [Line Items]
Gain on sale				$ 5.7
Cash proceed from sale				$ 2.6
Gross & Janes Co [Member]
Business Acquisition [Line Items]
Value of the assets acquired									$ 15.5

Acquisitions, Divestitures and Discontinued Operations (Tables)

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Schedule of Fair Value of Assets and Liabilities Acquired

The fair value of assets and liabilities acquired is set forth in the following table:


(Dollars in millions)
Accounts receivable	$	4.3
Inventory		7.4
Property, plant and equipment		4.5
Total assets acquired		16.2
Accounts payable and accrued liabilities		0.7
Net assets acquired	$	15.5

Derivative Financial Instruments - Schedule of Unrealized Gain (Loss) from Contract Where Hedge Accounting Was Not Elected (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Hedges [Member] \| Contracts Where Hedge Accounting Was not Elected [Member]
Derivative [Line Items]
Gain (loss) from contracts where hedge accounting was not elected	$ 0.9	$ (6.5)	$ (3.8)

Goodwill and Other Identifiable Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	$ 294.0	$ 296.0
Currency translation	0.4	(2.0)
Balance ending	294.4	294.0
Performance Chemicals [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	173.4	175.1
Currency translation	0.4	(1.7)
Balance ending	173.8	173.4
Railroad Products and Services [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	41.0	41.1
Currency translation	0.0	(0.1)
Balance ending	41.0	41.0
Utility Products [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	79.6	79.8
Currency translation	0.0	(0.2)
Balance ending	$ 79.6	$ 79.6

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References + Details

Stock-based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based Compensation

8. Stock-based Compensation

We have outstanding stock-based compensation awards that were granted under the amended and restated 2005 Long-Term Incentive Plan (the 2005 LTIP), the 2018 Long-Term Incentive Plan (the 2018 LTIP) and the 2020 Long-Term Incentive Plan, as amended (the 2020 LTIP). The 2005 LTIP, the 2018 LTIP and the 2020 LTIP are collectively referred to as the LTIP. The LTIP provides for the grant to eligible persons of stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance awards, dividend equivalents and other stock-based awards, which are collectively referred to as the awards.

Restricted Stock Units and Performance Stock Units

Under the LTIP, the board of directors grants restricted stock units and performance stock units to certain employee participants (collectively, the stock units). Compensation expense for non-vested stock units is recorded over the vesting period based on the fair value at the date of grant. The fair value of restricted stock units is the market price of the underlying common stock on the date of grant. The fair value of performance stock units is determined using the market price of the underlying common stock on the date of grant for units with a performance condition and a Monte Carlo valuation model for units with a market condition.

For grants to most employees prior to 2023, the restricted stock units vest in four equal annual installments. Starting in 2023, most grants of restricted stock units vest in three years. Restricted stock units that have one-year vesting periods are also issued under the LTIP to members of the board of directors in connection with annual director compensation and, from time to time, are issued to employees with vesting periods of typically two years or less.

Performance stock units have vesting based upon either a performance condition or a market condition. Performance stock units granted with a performance condition have a cumulative three-year performance objective based on adjusted EBITDA (see Note 9 – Segment Information). For performance stock units granted with a market condition, which applies to all performance stock unit grants made prior to 2023, the applicable objective is based on our total shareholder return relative to the Standard & Poor’s SmallCap 600 Materials Index and has multi-year performance objectives.

Both types of performance stock units have a three-year period for vesting. The number of performance stock units granted represents the target award, and participants have the ability to earn between zero and 200 percent of the target award based upon actual performance. If minimum performance criteria are not achieved, no performance stock units will vest. We have the discretion to settle the award in cash rather than shares, although we currently expect that all awards will be settled by the issuance of shares.

We calculated the fair value of the performance stock unit awards on the date of the grant using assumptions listed below:


	January 2023 Grant			January 2022 Grant			January 2021 Grant
Grant date price per share of stock performance award	$	29.01		$	32.19		$	29.84
Expected volatility		66.30	%		66.90	%		68.70	%
Risk-free interest rate		4.11	%		1.10	%		0.16	%
Look-back period in years		3.00			3.00			3.00
Grant date fair value per share	$	39.51		$	45.19		$	41.50

Dividends declared, if any, on our common stock during the period prior to vesting of the stock units are credited at equivalent value as additional stock units and become payable as additional common shares upon vesting. In the event of termination of employment, other than retirement, death or disability, any non-vested stock units are forfeited, including additional stock units credited from dividends. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the stock units over the service period will result. There are special vesting provisions for the stock units related to a change in control.

The following table shows a summary of the performance stock units as of December 31, 2023:


Performance Period	Minimum Shares		Target Shares		Maximum Shares
Market Condition Units
2021 – 2023		136,560		136,560		136,560
2022 – 2024		97,870		149,246		200,622
2023 – 2025		52,598		105,196		157,794
Performance Condition Units
2023 – 2025		0		189,084		378,168

The minimum, target and maximum shares above reflect the impact from completed performance periods. Performance stock units granted in January 2021 for the 2021 – 2023 performance period vested in January 2024 at 94.7 percent of the original target share amount plus dividend equivalent units.

The following table shows a summary of the status and activity of non-vested stock awards:


	Restricted Stock Units			Performance Stock Units			Total Stock Units			Weighted Average Grant Date Fair Value per Unit
Non-vested at January 1, 2023		524,612			237,032			761,644		$	32.40
Granted		238,544			267,073			505,617		$	30.92
Credited from dividends		6,394			4,604			10,998		$	32.37
Performance share adjustment		0			78,468			78,468		$	42.18
Vested		(222,250	)		0			(222,250	)	$	26.44
Forfeited		(15,961	)		(6,414	)		(22,375	)	$	32.00
Non-vested at December 31, 2023		531,339			580,763			1,112,102		$	33.62

Stock Options

Stock options to most executive officers vest and become exercisable in four equal annual installments. The stock options have a term of ten years. In the event of termination of employment, other than retirement, death or disability, any non-vested options are forfeited. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the options over the service period will result. There are special vesting provisions for the stock options related to a change in control. No stock options were granted in 2023.

Compensation expense for non-vested stock options is recorded over the vesting period based on the fair value at the date of grant. We calculated the fair value of stock options on the date of grant using the Black-Scholes-Merton model and the assumptions listed below:


	January 2022 Grant			January 2021 Grant			March 2020 Grant
Grant date price per share of stock option award	$	32.19		$	29.84		$	19.63
Expected life in years		6.76			6.64			6.40
Expected volatility		54.50	%		54.80	%		42.85	%
Risk-free interest rate		1.52	%		0.59	%		0.87	%
Grant date fair value per share	$	17.58		$	15.79		$	8.42

Prior to February 2022, we had not declared a dividend since 2014. The expected life in years is based on our historical exercise data of previously granted options. Expected volatility is based on the historical volatility of our common stock. The risk-free interest rate is based on U.S. Treasury bill rates for the expected life of the option.

The following table shows a summary of the status and activity of stock options:


	Options			Weighted Average Exercise Price per Option		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2022		1,122,136		$	27.05
Exercised		(365,237	)	$	24.11
Expired		(50,031	)	$	42.16
Outstanding at December 31, 2023		706,868		$	27.51		5.02	$	16.8
Exercisable at December 31, 2023		545,392		$	27.29		4.35	$	13.0

Stock Compensation Expense

The following table presents total stock-based compensation expense recognized under our LTIP and employee stock purchase plan:


	Year Ended December 31,
	2023		2022		2021
(Dollars in millions)
Stock-based compensation expense recognized:
Selling, general and administrative expenses	$	17.3	$	13.2	$	13.0
Less related income tax benefit		4.8		4.4		3.7
Decrease in net income attributable to Koppers	$	12.5	$	8.8	$	9.3
Intrinsic value of exercised stock options	$	6.4	$	0.0	$	2.2
Cash received from the exercise of stock options	$	8.8	$	0.0	$	2.3

As of December 31, 2023, total future compensation expense related to non-vested stock-based compensation arrangements totaled $21.7 million and the weighted-average period over which this expense is expected to be recognized is approximately 21 months.

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Asset Retirement Obligation Liabilities

The following table describes changes to our asset retirement obligation liabilities:


	December 31,
	2023			2022
(Dollars in millions)
Asset retirement obligation at beginning of year	$	15.5		$	13.2
Accretion expense		1.1			1.1
Revision in estimated cash flows		(0.8	)		2.2
Cash expenditures		(0.6	)		(1.0	)
Balance at end of year	$	15.2		$	15.5

Pensions and Post-Retirement Benefit Plans - Schedule of Pension Plan Assets at Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 128.1	$ 127.4
Investments measured at NAV	91.2	36.0
Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	36.9	91.4
Fair Value, Recurring \| Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	3.5	59.9
Fair Value, Recurring \| Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	33.4	31.5
Fair Value, Recurring \| U.S. equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.1	4.9
Fair Value, Recurring \| U.S. equity securities [Member] \| Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| U.S. equity securities [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.1	4.9
Fair Value, Recurring \| U.S. equity securities [Member] \| Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| Insurance Annuity Contract and Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	33.8
Fair Value, Recurring \| Insurance Annuity Contract and Other Investments [Member] \| Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0
Fair Value, Recurring \| Insurance Annuity Contract and Other Investments [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.4
Fair Value, Recurring \| Insurance Annuity Contract and Other Investments [Member] \| Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	33.4
Fair Value, Recurring \| International equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.4	11.1
Fair Value, Recurring \| International equity securities [Member] \| Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| International equity securities [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.4	11.1
Fair Value, Recurring \| International equity securities [Member] \| Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| U.S. debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.3	39.2
Fair Value, Recurring \| U.S. debt securities [Member] \| Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| U.S. debt securities [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.3	39.2
Fair Value, Recurring \| U.S. debt securities [Member] \| Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| International debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.8	2.6
Fair Value, Recurring \| International debt securities [Member] \| Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| International debt securities [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.8	2.6
Fair Value, Recurring \| International debt securities [Member] \| Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| Cash & Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.5	1.6
Fair Value, Recurring \| Cash & Cash Equivalents [Member] \| Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Fair Value, Recurring \| Cash & Cash Equivalents [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.5	1.6
Fair Value, Recurring \| Cash & Cash Equivalents [Member] \| Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0.0	0.0
Fair Value, Recurring \| Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		32.0
Fair Value, Recurring \| Other Investments [Member] \| Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0.0
Fair Value, Recurring \| Other Investments [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0.5
Fair Value, Recurring \| Other Investments [Member] \| Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		$ 31.5