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Asset Retirement Obligation Disclosure [Abstract]

Debt

14. Debt

Debt as of June 30, 2018 and December 31, 2017 was as follows:

	Weighted Average Interest Rate			Maturity	June 30, 2018		December 31, 2017
(Dollars in millions)
Term Loan		5.12	%	2023	$	97.5	$	0.0
Revolving Credit Facility		5.12	%	2023		390.1		155.0
Construction and other loans		4.69	%	2020		25.9		33.7
Senior Notes due 2025		6.00	%	2025		500.0		500.0
Debt						1,013.5		688.7
Less short-term debt and current maturities of long-term debt						15.3		11.4
Less unamortized debt issuance costs						13.4		11.7
Long-term debt					$	984.8	$	665.6

Senior Notes due 2025

The 2025 Notes are senior obligations, are unsecured and are guaranteed by Koppers Holdings Inc. and certain of Koppers Inc.’s domestic subsidiaries. The 2025 Notes pay interest semi-annually in arrears on February 15 and August 15 beginning on August 15, 2017 and will mature on February 15, 2025 unless earlier redeemed or repurchased. On or after February 15, 2020, the Company is entitled to redeem all or a portion of the 2025 Senior Notes at a redemption price of 104.5 percent of principal value, declining to a redemption price of 101.5 percent on or after February 15, 2022 until the redemption price is equivalent to the principal value on April 15, 2023.

The indenture governing the 2025 Senior Notes includes customary covenants that restrict, among other things, the ability of Koppers Inc. and its restricted subsidiaries to incur additional debt, pay dividends or make certain other restricted payments, incur liens, merge or sell all or substantially all of the assets of Koppers Inc. or its subsidiaries or enter into various transactions with affiliates.

Revolving Credit Facility

On April 10, 2018, the Company amended its $600 million Revolving Credit Facility to enter into a new Secured Term Loan Facility. The new Secured Term Loan Facility includes the $600 million Revolving Credit Facility and a secured term loan of $100 million with a quarterly amortization of $2.5 million and a five-year maturity. In addition, the maturity date of the amended Revolving Credit Facility was extended one year to April 2023. The interest rate on the amended Revolving Credit Facility is variable and is based on LIBOR. The initial average borrowing rates under both facilities are expected to be approximately five percent. Terms under the amended Revolving Credit Facility are substantially consistent with the original Revolving Credit Facility.

Borrowings under the Revolving Credit Facility are secured by a first priority lien on substantially all of the assets of Koppers Inc., Koppers Holdings and their material domestic subsidiaries. The Revolving Credit Facility contains certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends, investments or acquisitions. In addition, such covenants give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios.

As of June 30, 2018, the Company had $176.2 million of unused revolving credit availability for working capital purposes after restrictions from certain letter of credit commitments and other covenants. As of June 30, 2018, $33.8 million of commitments were utilized by outstanding letters of credit.

Loss on Extinguishment of Debt

In February 2017, all of the outstanding Koppers Inc. senior notes due 2019 were repurchased at a premium to carrying value and accordingly, the Company realized a loss on extinguishment of debt totaling $10.0 million consisting of $7.3 million for bond premium and bond tender expenses and $2.7 million for the write-off of unamortized debt issuance costs.

Also in February 2017, Koppers Inc. repaid its term loan in full and entered into a new Revolving Credit Facility. Accordingly, the Company realized a loss of $3.3 million for the write-off of unamortized debt issuance costs.

Construction Loans

The Company’s 75-percent owned subsidiary, Koppers (Jiangsu) Carbon Chemical Company Limited (“KJCC”) entered into committed loan facility agreements with a third-party bank and the 25-percent non-controlling shareholder in KJCC. Borrowings under the third-party bank facility, which includes a construction loan and a working capital facility, totaled $23.1 million at June 30, 2018 and are secured by a letter of credit issued by a bank under the Revolving Credit Facility. KJCC will repay the construction loan portion of the third-party commitment in six installments every six months starting in June 2018 with a final repayment on December 21, 2020, the maturity date of the loans.

Asset Retirement Obligations

6 Months Ended

Jun. 30, 2018

Asset Retirement Obligations

15. Asset Retirement Obligations

The Company recognizes 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 reflects changes in the carrying values of asset retirement obligations:

	June 30, 2018			December 31, 2017
(Dollars in millions)
Asset retirement obligation at beginning of year	$	37.1		$	36.0
Accretion expense		0.8			2.4
Revision in estimated cash flows		0.7			9.4
Cash expenditures		(5.7	)		(10.9	)
Currency translation		0.0			0.2
Balance at end of period	$	32.9		$	37.1

Deferred Revenue

6 Months Ended

Jun. 30, 2018

Deferred Revenue Disclosure [Abstract]

Deferred Revenue

16. Deferred Revenue

In 2015, KJCC received a cash advance payment of $30 million as part of an amendment to a soft pitch supply agreement with its customer. Also, the Company defers revenues associated with extended product warranty liabilities based on historical loss experience and sales of extended warranties on certain products. The following table reflects changes in the carrying values of deferred revenue:

	June 30, 2018			December 31, 2017
(Dollars in millions)
Balance at beginning of year	$	28.1		$	27.2
Revenue earned		(0.3	)		(0.7	)
Currency translation		(0.5	)		1.6
Balance at end of period	$	27.3		$	28.1

Deferred revenue classified in other long-term liabilities in the consolidated balance sheet totaled $26.4 million as of June 30, 2018 and $27.2 million as of December 31, 2017 with the remainder classified in accrued liabilities.

Derivative Financial Instruments

6 Months Ended

Jun. 30, 2018

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Derivative Financial Instruments

17. Derivative Financial Instruments

The Company utilizes derivative instruments to manage exposures to risks that have been identified and measured and are capable of being controlled. The primary risks managed by the company by using derivative instruments are commodity price risk associated with copper and foreign currency exchange risk associated with a number of currencies, principally the U.S. dollar, the Canadian dollar, the New Zealand dollar, the Euro and British pounds. Swap contracts on copper are used to manage the price risk associated with forecasted purchases of materials used in the Company’s manufacturing processes. Generally, the Company will not hedge cash flow exposures for durations longer than 36 months and the Company has hedged certain volumes of copper through December 2020. The Company enters into foreign currency forward contracts to manage foreign currency risk associated with the Company’s receivable and payable balances and foreign currency denominated sales. Generally, the Company enters into master netting arrangements with the counterparties and offsets net derivative positions with the same counterparties. Currently, the Company’s agreements do not require cash collateral.

ASC Topic 815-10, “Derivatives and Hedging,” requires companies to recognize all derivative instruments as either assets or liabilities at fair value in the balance sheet. Derivative instruments’ fair value is determined using significant other observable inputs, or Level 2 in the fair value hierarchy. In accordance with ASC Topic 815-10, the Company designates certain of its commodity swaps as cash flow hedges of forecasted purchases of commodities and certain of its foreign currency swaps as cash flow hedges of forecasted sales. 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 either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current earnings. The amount of hedge ineffectiveness charged to profit and loss is reported in the table below.

For those commodity and foreign currency swaps which are not designated as cash flow hedges, the fair value of the swap is recognized as an asset or liability in the consolidated balance sheet and the related gain or loss on the derivative is reported in current earnings.

As of June 30, 2018 and December 31, 2017, the Company had outstanding copper swap contracts of the following amounts:

	Units Outstanding (in Pounds)		Net Fair Value - Asset
	June 30, 2018	December 31, 2017	June 30, 2018		December 31, 2017
(Amounts in millions)
Cash flow hedges	35.2	37.8	$	8.3	$	25.5
Not designated as hedges	10.1	11.3		0.1		4.5
Total	45.3	49.1	$	8.4	$	30.0

As of June 30, 2018 and December 31, 2017, the fair value of the outstanding copper swap contracts is recorded in the balance sheet as follows:

	June 30, 2018			December 31, 2017
(Dollars in millions)
Other current assets	$	6.5		$	21.8
Other assets		2.0			8.2
Accrued liabilities		(0.1	)		0.0
Net asset on balance sheet	$	8.4		$	30.0
Accumulated other comprehensive gain, net of tax	$	6.2		$	15.8

Based upon contracts outstanding at June 30, 2018, in the next twelve months the Company estimates that $5.2 million of unrealized gains, net of tax, related to commodity price hedging will be reclassified from other comprehensive loss into earnings.

See Note 6 – Comprehensive Income (Loss) and Equity, for amounts recorded in other comprehensive income and for amounts reclassified from accumulated other comprehensive loss to net income for the periods specified below. For the three and six months ended June 30, 2018 and 2017, the following amounts were recognized in earnings related to copper swap contracts:

	Three Months Ended June 30,					Six Months Ended June 30,
	2018			2017		2018			2017
(Dollars in millions)
Gain from ineffectiveness of cash flow hedges	$	0.0		$	1.1	$	0.0		$	3.0
(Loss) gain from contracts not designated as hedges		(1.0	)		0.3		(4.5	)		1.0
Net	$	(1.0	)	$	1.4	$	(4.5	)	$	4.0

The fair value associated with forward contracts related to foreign currency that are not designated as hedges are immediately charged to earnings. These amounts are classified in cost of sales in the Condensed Consolidated Statement of Operations and Comprehensive Income. As of June 30, 2018, the Company had outstanding foreign currency forward contracts consisting of a gross derivative liability of $1.4 million (recognized in accrued liabilities in the balance sheet) and a gross derivative asset of $1.3 million (recognized in other current assets in the balance sheet). As of December 31, 2017, the Company had outstanding currency forward contracts with a net fair value totaling $0.1 million, consisting of a gross derivative liability of $0.2 million (recognized in accrued liabilities in the balance sheet) and a gross derivative asset of $0.3 million (recognized in other current assets in the balance sheet).

As of June 30, 2018 and December 31, 2017, the net currency units outstanding for these contracts were:

	June 30, 2018		December 31, 2017
(In millions)
British Pounds		GBP 6.2		GBP 7.0
New Zealand Dollars		NZD 16.0		NZD 15.5
United States Dollars		USD 1.4		USD 12.5
Canadian Dollars		CAD 2.5		CAD 2.5
Euro		EUR 0.3		EUR 0.0

Commitments and Contingent Liabilities

6 Months Ended

Jun. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingent Liabilities

18. Commitments and Contingent Liabilities

The Company and its subsidiaries are involved in litigation and various proceedings relating to environmental laws and regulations, toxic tort, 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 the Company or its subsidiaries fail to prevail in any of these legal matters or should several of these legal matters be resolved against the Company or its subsidiaries 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 are 85 plaintiffs in 47 cases pending as of June 30, 2018, compared to 87 plaintiffs in 48 cases as of December 31, 2017. As of June 30, 2018, there are 46 cases pending in state court in Pennsylvania, and 1 case pending in state court in Tennessee.

The plaintiffs in all 47 pending cases seek to recover compensatory damages. Plaintiffs in 43 of those cases also seek to recover punitive damages. The plaintiffs in the 46 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, Dow Chemical Company, 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.

The Company has not provided a reserve for these lawsuits because, at this time, the Company 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 the Company’s business, financial condition, cash flows and results of operations.

Environmental and Other Litigation Matters

The Company and its subsidiaries 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. The Company’s subsidiaries expect to incur substantial costs for ongoing compliance with such laws and regulations. The Company’s subsidiaries 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. The Company accrues 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. The Company’s subsidiaries have agreements with former owners of certain of their operating locations under which the former owners retained, assumed and/or agreed to indemnify such subsidiaries 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 “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 through July 2019. As consideration for the amendment, Koppers Inc. paid Beazer East a total of $7.0 million and agreed to share toxic tort litigation defense costs arising from any sites acquired from Beazer East. The July 2004 amendment 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 asserted after July 2019.

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. If the third-party claims described in sections (i) and (ii) above are not made by July 2019, Beazer East will not be required to pay the costs arising from such claims under the Indemnity. However, with respect to any such claims which are made by July 2019, Beazer East will continue to be responsible for such claims under the Indemnity beyond July 2019. 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 the Company’s 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 the Company against the liabilities referred to above, including Beazer East, have performed their obligations in all material respects. The Company believes that, for the last three years ended December 31, 2017, amounts paid by Beazer East as a result of its environmental remediation obligations under the Indemnity have averaged, in total, approximately $10 million per year. 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 the Company or its subsidiaries are held liable for or otherwise required to pay all or part of such liabilities without reimbursement, the imposition of such liabilities on the Company or its subsidiaries could have a material adverse effect on its business, financial condition, cash flows and results of operations. Furthermore, the Company could be required to record a contingent liability on its balance sheet with respect to such matters, which could result in a negative impact to the Company’s business, financial condition, cash flows and results of operations.

Domestic Environmental Matters. On June 4, 2018, Koppers Inc. received a letter from the U.S. Environmental Protection Agency ("EPA") concerning potential violations of the Clean Water Act observed during inspections and review of Spill Prevention, Control and Countermeasure Plans and Facility Response Plans at the Company’s facilities in Follansbee, WV; Green Spring, WV; and Clairton, PA. In addition, the EPA reviewed one facility’s compliance with an earlier consent order regarding above ground storage tank integrity testing. The Company met with the EPA on June 28, 2018 to discuss and present relevant information related to the allegations. The Company currently cannot estimate the potential penalties, fines or other expenditures, if any, that may result from any EPA actions relating to the alleged potential violations and, therefore, the Company cannot determine if the ultimate outcome of this matter will have a material impact on the Company's financial position, results of operations or cash flows.

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 Environmental Protection Agency (“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. 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. Responsibility for implementing and funding that work will be decided in the separate private allocation process, which is ongoing.

Additionally, the Company is involved in two separate natural resource damages assessments at the Portland Harbor site. An assessment is intended to identify damages to natural resources caused by the releases of hazardous substances to the Willamette River and to serve 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. One of the natural resource damage assessments was filed in January 2017 by the Yakama Nation in Oregon federal court. Yakama Nation seeks recovery for future response costs and the costs of assessing injury to natural resources and recovery for past costs of overseeing investigations conducted on the site. Motions to dismiss the case are pending.

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.

The Company has accrued the estimated costs of participating in the PRP group at the Portland Harbor and Newark Bay CERCLA sites and estimated de minimis settlement amounts at the sites totaling $2.1 million at June 30, 2018. 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 the Company’s business, financial condition, cash flows and results of operations.

There are two plant sites in the United States related to the Performance Chemicals business where the Company has recorded an environmental remediation liability for soil and groundwater contamination which occurred prior to the Company’s acquisition of the business. As of June 30 2018, the Company’s estimated environmental remediation liability for these acquired sites totals $4.9 million.

There is one plant site in the United States related to the Utility and Industrial Products business where the Company has recorded an environmental remediation liability for soil and groundwater contamination which occurred prior to the Company’s acquisition of the business. As of June 30, 2018, the Company’s estimated environmental remediation liability for the acquired site totals $1.9 million.

Foreign Environmental Matters. There are two plant sites related to the Performance Chemicals business located in the United Kingdom and Australia where the Company has recorded an environmental remediation liability for soil and groundwater contamination which occurred prior to the acquisition of the business. As of June 30, 2018, the Company’s estimated environmental remediation liability for these acquired sites totals $2.6 million.

In December 2011, the Company ceased manufacturing operations at its Continental Carbon facility located in Kurnell, Australia. The Company has accrued its expected cost of site remediation resulting from the closure of $0.7 million as of June 30, 2018.

Environmental Reserves Rollforward. The following table reflects changes in the accrued liability for environmental matters, of which $4.5 million and $5.1 million are classified as current liabilities at June 30, 2018 and December 31, 2017, respectively:

	Period ended
	June 30, 2018			December 31, 2017
(Dollars in millions)
Balance at beginning of year	$	13.9		$	12.9
Expense		1.0			3.2
Reversal of reserves		0.0			(0.7	)
Cash expenditures		(2.9	)		(1.8	)
Acquisition		1.9			0.0
Currency translation		(0.3	)		0.3
Balance at end of period	$	13.6		$	13.9

Subsidiary Guarantor Information for Koppers Inc. Shelf Registration

6 Months Ended

Jun. 30, 2018

Subsidiary Guarantor Information for Koppers Inc. Shelf Registration

19. Subsidiary Guarantor Information for Koppers Inc. Shelf Registration

Under a registration statement on Form S-3, Koppers Holdings may sell a combination of securities, including common stock, debt securities, preferred stock, depository shares, warrants, purchase contracts and units, from time to time in one or more offerings. In addition, Koppers Inc. may sell debt securities from time to time under the registration statement. Debt securities may be fully and unconditionally guaranteed, on a joint and several basis, by Koppers Holdings, Koppers Inc., Koppers Asia LLC, Koppers World-Wide Ventures Corporation, Koppers Concrete Products, Inc., Concrete Partners, Inc., Koppers Delaware, Inc., Koppers Ventures, Inc., Koppers Performance Chemicals Inc., Koppers-Nevada Limited Liability Company, Koppers NZ LLC, Koppers Railroad Structures Inc., Wood Protection LP and Wood Management LLC. Non-guarantor subsidiaries are owned directly or indirectly by Koppers Inc. or are owned directly or indirectly by Koppers World-Wide Ventures Corporation. The guarantor subsidiaries that issue guarantees, if any, will be determined when a debt offering actually occurs under the registration statement and accordingly, the condensed consolidating financial information for subsidiary guarantors will be revised to identify the subsidiaries that actually provided guarantees. These guarantees will be governed pursuant to a supplemental indenture which the trustee and the issuing company would enter into concurrent with the debt offering.

Reliance of Koppers Holdings on Earnings of Koppers Inc. and its Subsidiaries

Koppers Holdings depends on the dividends from the earnings of Koppers Inc. and its subsidiaries to generate the funds necessary to meet its financial obligations, including the payment of any declared dividend of Koppers Holdings. The Revolving Credit Facility prohibits Koppers Inc. from making dividend payments to Koppers Holdings unless (1) such dividend payments are permitted by the indenture governing Koppers Inc.’s 2025 Notes, (2) no event of default or potential default has occurred or is continuing under the credit agreement, and (3) the Company is in pro forma compliance with the Company’s fixed charge coverage ratio covenant after giving effect to such dividend. The indenture governing the 2025 Notes restrict Koppers Inc.’s ability to finance the Company’s payment of dividends if (1) a default has occurred or would result from such financing, (2) Koppers Inc., or a restricted subsidiary of Koppers Inc. which is not a guarantor under the applicable indenture is not able to incur additional indebtedness (as defined in the applicable indenture), and (3) the sum of all restricted payments (as defined in the applicable indenture) have exceeded the permitted amount (which the Company refers to as the “basket”) at such point in time.

The Koppers Inc. Revolving Credit Facility agreement provides for a revolving credit facility at variable rates. Borrowings under the Revolving Credit Facility are secured by a first priority lien on substantially all of the assets of Koppers Inc. and its material domestic subsidiaries. The revolving credit facility agreement contains certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends, investments or acquisitions. In addition, such covenants give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios.

As of June 30, 2018, Koppers Inc.’s assets exceeded its liabilities by $90.1 million. There are no net assets unavailable for distribution to Koppers Holdings Inc. by Koppers Inc. as of June 30, 2018. Cash dividends paid to Koppers Holdings Inc. by its subsidiaries totaled $7.4 million and $2.0 million for the six months ended June 30, 2018 and 2017, respectively.

Condensed Consolidating Statement of Operations

For the Three Months Ended June 30, 2018

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Net sales	$	0.0		$	140.2		$	95.9	$	218.8		$	(18.9	)	$	436.0
Cost of sales including depreciation and amortization		0.0			129.3			72.1		186.6			(20.1	)		367.9
Selling, general and administrative		0.8			15.2			11.9		17.9			0.0			45.8
Operating profit (loss)		(0.8	)		(4.3	)		11.9		14.3			1.2			22.3
Other (loss) income		0.0			(2.4	)		0.4		1.3			0.0			(0.7	)
Equity income (loss) of subsidiaries		1.2			21.9			16.3		(0.1	)		(39.3	)		0.0
Interest expense		0.0			13.9			0.0		0.6			0.0			14.5
Income taxes		(0.2	)		0.1			2.7		4.0			0.0			6.6
Income from continuing operations		0.6			1.2			25.9		10.9			(38.1	)		0.5
Discontinued operations		0.0			0.0			0.0		0.5			0.0			0.5
Noncontrolling interests		0.0			0.0			0.0		0.4			0.0			0.4
Net income attributable to Koppers	$	0.6		$	1.2		$	25.9	$	11.0		$	(38.1	)	$	0.6
Comprehensive income attributable to Koppers	$	(20.4	)	$	(20.0	)	$	4.7	$	(5.9	)	$	21.2		$	(20.4	)

Condensed Consolidating Statement of Operations

For the Three Months Ended June 30, 2017

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Net sales	$	0.0		$	153.2		$	94.2		$	151.8		$	(21.2	)	$	378.0
Cost of sales including depreciation and amortization		0.0			141.8			65.1			123.0			(21.5	)		308.4
Selling, general and administrative		0.5			10.9			10.1			10.0			0.0			31.5
Operating profit (loss)		(0.5	)		0.5			19.0			18.8			0.3			38.1
Other income (loss)		0.0			(0.4	)		0.6			0.3			(0.3	)		0.2
Equity income (loss) of subsidiaries		20.0			25.5			12.9			(0.1	)		(58.3	)		0.0
Interest expense		0.0			10.0			(0.1	)		1.2			(0.3	)		10.8
Loss on extinguishment of debt		0.0			0.0			0.0			0.0			0.0			0.0
Income taxes		(0.2	)		(4.4	)		7.2			4.0			0.0			6.6
Income (loss) from continuing operations		19.7			20.0			25.4			13.8			(58.0	)		20.9
Discontinued operations		0.0			0.0			0.0			(1.1	)		0.0			(1.1	)
Noncontrolling interests		0.0			0.0			0.0			0.1			0.0			0.1
Net income attributable to Koppers	$	19.7		$	20.0		$	25.4		$	12.6		$	(58.0	)	$	19.7
Comprehensive income (loss) attributable to Koppers	$	24.5		$	24.8		$	29.9		$	18.5		$	(73.2	)	$	24.5

Condensed Consolidating Statement of Operations

For the Six Months Ended June 30, 2018

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Net sales	$	0.0		$	271.3		$	173.4	$	434.5		$	(37.1	)	$	842.1
Cost of sales including depreciation and amortization		0.0			252.2			134.4		344.3			(38.3	)		692.6
Selling, general and administrative		1.4			27.3			23.9		31.3			0.0			83.9
Operating profit (loss)		(1.4	)		(8.2	)		15.1		58.9			1.2			65.6
Other (loss) income		0.0			(2.8	)		0.8		1.5			0.0			(0.5	)
Equity income (loss) of subsidiaries		19.5			58.4			49.9		(0.1	)		(127.7	)		0.0
Interest expense		0.0			23.8			0.0		1.2			0.0			25.0
Income taxes		(0.3	)		4.1			3.6		8.4			0.0			15.8
Income from continuing operations		18.4			19.5			62.2		50.7			(126.5	)		24.3
Discontinued operations		0.0			0.0			0.0		0.4			0.0			0.4
Noncontrolling interests		0.0			0.0			0.0		6.3			0.0			6.3
Net income attributable to Koppers	$	18.4		$	19.5		$	62.2	$	44.8		$	(126.5	)	$	18.4
Comprehensive income attributable to Koppers	$	(10.3	)	$	(9.4	)	$	32.7	$	28.7		$	(52.0	)	$	(10.3	)

Condensed Consolidating Statement of Operations

For the Six Months Ended June 30, 2017

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Net sales	$	0.0		$	304.1		$	175.4	$	288.2		$	(43.1	)	$	724.6
Cost of sales including depreciation and amortization		0.0			289.5			119.1		228.8			(41.4	)		596.0
Selling, general and administrative		1.0			21.7			20.3		19.4			0.0			62.4
Operating profit (loss)		(1.0	)		(7.1	)		36.0		40.0			(1.7	)		66.2
Other income		0.0			(0.8	)		1.2		1.8			(0.5	)		1.7
Equity income of subsidiaries		24.9			51.8			30.3		(0.1	)		(106.9	)		0.0
Interest expense		0.0			19.7			0.0		2.1			(0.4	)		21.4
Loss on extinguishment of debt		0.0			13.3			0.0		0.0			0.0			13.3
Income taxes		(0.2	)		(14.0	)		13.7		8.1			0.0			7.6
Income from continuing operations		24.1			24.9			53.8		31.5			(108.7	)		25.6
Discontinued operations		0.0			0.0			0.0		(1.2	)		0.0			(1.2	)
Noncontrolling interests		0.0			0.0			0.0		0.3			0.0			0.3
Net income attributable to Koppers	$	24.1		$	24.9		$	53.8	$	30.0		$	(108.7	)	$	24.1
Comprehensive income attributable to Koppers	$	36.5		$	37.4		$	65.8	$	42.0		$	(145.2	)	$	36.5

Condensed Consolidating Balance Sheet

June 30, 2018

	Parent		Koppers Inc.		Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating Adjustments			Consolidated
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0.0	$	0.3	$	0.1		$	62.1	$	0.0		$	62.5
Receivables, net		0.0		61.1		39.0			117.6		0.0			217.7
Affiliated receivables		1.1		12.8		8.7			6.4		(29.0	)		0.0
Inventories, net		0.0		100.5		45.7			150.5		(0.8	)		295.9
Other current assets		0.0		6.4		8.3			18.1		0.4			33.2
Total current assets		1.1		181.1		101.8			354.7		(29.4	)		609.3
Equity investments		89.4		1,014.1		310.4			0.1		(1,414.0	)		0.0
Property, plant and equipment, net		0.0		190.4		46.7			147.4		0.0			384.5
Goodwill		0.0		0.8		153.1			142.5		0.0			296.4
Intangible assets, net		0.0		7.0		94.1			97.6		0.0			198.7
Deferred tax assets		0.0		24.4		(9.1	)		2.8		0.0			18.1
Affiliated loan receivables		0.0		41.4		149.2			7.7		(198.3	)		0.0
Other assets		0.0		4.7		6.2			13.8		0.0			24.7
Total assets	$	90.5	$	1,463.9	$	852.4		$	766.6	$	(1,641.7	)	$	1,531.7
LIABILITIES AND EQUITY
Accounts payable		0.0		79.9		40.9			53.6		0.0			174.4
Affiliated payables		0.0		19.3		2.5			8.0		(29.8	)		0.0
Accrued liabilities		0.0		53.5		16.5			40.0		0.0			110.0
Current maturities of long-term debt		0.0		10.1		0.1			5.1		0.0			15.3
Total current liabilities		0.0		162.8		60.0			106.7		(29.8	)		299.7
Long-term debt		0.0		964.1		0.2			20.5		0.0			984.8
Affiliated debt		0.0		156.1		33.1			9.1		(198.3	)		0.0
Other long-term liabilities		0.0		90.8		14.1			40.2		0.0			145.1
Total liabilities		0.0		1,373.8		107.4			176.5		(228.1	)		1,429.6
Koppers shareholders’ equity		90.5		90.1		745.0			578.4		(1,413.6	)		90.4
Noncontrolling interests		0.0		0.0		0.0			11.7		0.0			11.7
Total liabilities and equity	$	90.5	$	1,463.9	$	852.4		$	766.6	$	(1,641.7	)	$	1,531.7

Condensed Consolidating Balance Sheet

December 31, 2017

	Parent		Koppers Inc.			Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0.0	$	0.7		$	0.0		$	59.6		$	0.0		$	60.3
Receivables, net		0.0		48.6			27.7			84.6			0.0			160.9
Affiliated receivables		0.6		19.4			(83.0	)		(12.1	)		75.1			0.0
Inventories, net		0.0		80.4			40.5			117.9			(1.9	)		236.9
Deferred tax assets		0.0		0.0			0.0			(0.1	)		0.1			0.0
Other current assets		0.0		6.6			23.0			18.8			0.2			48.6
Total current assets		0.6		155.7			8.2			268.7			73.5			506.7
Equity investments		99.3		716.3			276.8			(0.1	)		(1,092.3	)		0.0
Property, plant and equipment, net		0.0		155.2			47.3			125.5			0.0			328.0
Goodwill		0.0		0.8			153.1			34.3			0.0			188.2
Intangible assets, net		0.0		7.2			96.7			25.7			0.0			129.6
Deferred tax assets		0.0		29.4			(13.2	)		2.2			0.0			18.4
Affiliated loan receivables		0.0		34.9			224.3			21.4			(280.6	)		0.0
Other assets		0.0		4.4			15.3			9.6			0.0			29.3
Total assets	$	99.9	$	1,103.9		$	808.5		$	487.3		$	(1,299.4	)	$	1,200.2
LIABILITIES AND EQUITY
Accounts payable	$	0.0	$	65.1		$	32.4		$	44.4		$	0.0		$	141.9
Affiliated payables		0.0		(90.3	)		13.8			2.2			74.3			0.0
Accrued liabilities		0.0		59.9			16.4			51.6			0.0			127.9
Current maturities of long-term debt		0.0		0.1			0.0			11.3			0.0			11.4
Total current liabilities		0.0		34.8			62.6			109.5			74.3			281.2
Long-term debt		0.0		643.3			0.0			22.3			0.0			665.6
Affiliated debt		0.0		233.7			19.3			27.6			(280.6	)		0.0
Other long-term liabilities		0.0		92.0			14.4			41.2			0.0			147.6
Total liabilities		0.0		1,003.8			96.3			200.6			(206.3	)		1,094.4
Koppers shareholders’ equity		99.9		100.1			712.2			280.8			(1,093.1	)		99.9
Noncontrolling interests		0.0		0.0			0.0			5.9			0.0			5.9
Total liabilities and equity	$	99.9	$	1,103.9		$	808.5		$	487.3		$	(1,299.4	)	$	1,200.2

Condensed Consolidating Statement of Cash Flows

For the Six Months Ended June 30, 2018

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Cash provided by (used in) operating activities	$	5.3		$	(34.0	)	$	9.7		$	29.5		$	(7.4	)	$	3.1
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0.0			(307.8	)		(1.9	)		(8.0	)		0.0			(317.7	)
Repayments (loans to) from affiliates		0.0			(0.4	)		(8.2	)		(3.7	)		12.3			0.0
Insurance proceeds received		0.0			0.0			0.0			0.7			0.0			0.7
Net cash provided by divestitures and asset sales		0.0			(2.1	)		0.0			3.6			0.0			1.5
Net cash (used in) provided by investing activities		0.0			(310.3	)		(10.1	)		(7.4	)		12.3			(315.5	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0.0			332.4			0.0			(7.7	)		0.0			324.7
Borrowings (repayments) of affiliated debt		0.0			21.8			0.5			(10.0	)		(12.3	)		0.0
Debt issuance costs		0.0			(2.9	)		0.0			0.0			0.0			(2.9	)
Dividends paid		0.0			(7.4	)		0.0			0.0			7.4			0.0
Stock repurchased		(5.3	)		0.0			0.0			0.1			0.0			(5.2	)
Net cash provided by (used in) financing activities		(5.3	)		343.9			0.5			(17.6	)		(4.9	)		316.6
Effect of exchange rates on cash		0.0			0.0			0.0			(2.0	)		0.0			(2.0	)
Net increase in cash and cash equivalents		0.0			(0.4	)		0.1			2.5			0.0			2.2
Cash and cash equivalents at beginning of year		0.0			0.7			0.0			59.6			0.0			60.3
Cash and cash equivalents at end of period	$	0.0		$	0.3		$	0.1		$	62.1		$	0.0		$	62.5

Condensed Consolidating Statement of Cash Flows

For the Six Months Ended June 30, 2017

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Cash provided by (used in) operating activities	$	3.3		$	(8.4	)	$	26.4		$	12.0		$	(2.0	)	$	31.3
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0.0			(23.1	)		(8.0	)		(3.1	)		0.0			(34.2	)
Repayments (loans to) from affiliates		0.0			2.9			(12.5	)		0.7			8.9			0.0
Repayment of loan		0.0			0.0			0.0			9.5			0.0			9.5
Net cash proceeds from divestitures and asset sales		0.0			0.0			0.5			0.3			0.0			0.8
Net cash (used in) provided by investing activities		0.0			(20.2	)		(20.0	)		7.4			8.9			(23.9	)
Cash provided by (used in) financing activities:
Repayments of long-term debt		0.0			30.0			0.0			(4.0	)		0.0			26.0
Borrowings (repayments) of affiliated debt		0.0			11.6			(6.4	)		3.7			(8.9	)		0.0
Deferred financing cost		0.0			(11.0	)		0.0			0.0			0.0			(11.0	)
Dividends paid		0.0			(2.0	)		0.0			0.0			2.0			0.0
Stock repurchased		(3.3	)		0.0			0.0			0.0			0.0			(3.3	)
Net cash provided by (used in) financing activities		(3.3	)		28.6			(6.4	)		(0.3	)		(6.9	)		11.7
Effect of exchange rates on cash		0.0			0.0			0.0			0.1			0.0			0.1
Net decrease in cash and cash equivalents		0.0			0.0			0.0			19.2			0.0			19.2
Cash and cash equivalents at beginning of year		0.0			0.0			0.0			20.8			0.0			20.8
Cash and cash equivalents at end of period	$	0.0		$	0.0		$	0.0		$	40.0		$	0.0		$	40.0

Related Party Transactions	6 Months Ended
Related Party Transactions	Jun. 30, 2018
Related Party Transactions [Abstract]
Related Party Transactions	20. Related Party Transactions During 2016, the Company sold its 30 percent interest in TKK. The Company had loaned $10.0 million, gross of accumulated equity losses of $1.1 million, to TKK, including interest. The loan and interest was fully repaid and the Company recorded a gain of $1.3 million in 2017. As disclosed in “Note 14 – Debt”, KJCC has an outstanding loan from its 25-percent non-controlling shareholder. The loan totals $2.5 million and matures in November 2018.

Fair Value Measurements

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

21. Fair Value Measurements

Carrying amounts and the related estimated fair values of the Company’s financial instruments as of June 30, 2018 and December 31, 2017 are as follows:

	June 30, 2018				December 31, 2017
	Fair Value		Carrying Value		Fair Value		Carrying Value
(Dollars in millions)
Financial assets:
Cash and cash equivalents, including restricted cash	$	62.5	$	62.5	$	60.3	$	60.3
Investments and other assets^(a)		1.1		1.1		1.1		1.1
Financial liabilities:
Long-term debt (including current portion)	$	1,003.5	$	1,013.5	$	706.9	$	688.7

(a)	Excludes equity method investments.

Cash and cash equivalents – The carrying value approximates fair value because of the short maturity of those instruments.

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 the Company’s long-term debt is estimated based on the market prices for the same or similar issues or on the current rates offered to the Company for debt of the same remaining maturities (Level 2). The fair value of the Company’s revolving credit facility approximates carrying value due to the variable rate nature of this instrument.

New Accounting Pronouncements (Policies)	6 Months Ended
New Accounting Pronouncements (Policies)	Jun. 30, 2018
Accounting Changes And Error Corrections [Abstract]
New Accounting Pronouncements	In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606).” ASU 2014-09 requires an entity to recognize revenue in a manner that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Subsequent to the issuance of ASU 2014-09, the FASB issued multiple ASUs which either amended or clarified ASU 2014-09. Collectively, the revenue recognition ASUs were effective for annual reporting periods beginning after December 15, 2017. The Company elected to use the modified retrospective method for transition in which the cumulative effect was recognized at its January 1, 2018 date of adoption with no restatement of comparative periods presented. The implementation of the guidance had no material impact on the measurement of recognition of revenue of prior periods; however, additional disclosures have been added in accordance with the ASU. In August 2017, the FASB issued ASU No. 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities.” This ASU amends and simplifies existing guidance in order to allow companies to more accurately present the economic effects of risk management activities in the financial statements. The Company adopted this ASU effective January 1, 2018 and the Company reclassified a $3.6 million unrealized gain, net of tax, from retained earnings to accumulated other comprehensive loss upon adoption. In March 2017, the FASB issued ASU 2017-07, “Compensation – Retirement Benefits (Topic 715)”, in order to improve the presentation of net periodic pension and postretirement costs. The amendment requires that an employer report the service cost component in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The amendments in this update related to income statement activity are applied. As a practical expedient, the Company has used the amounts disclosed in its pension and post-retirement benefits footnote as the estimation basis for applying the retrospective presentation requirements. The Company adopted this ASU effective January 1, 2018, and for retrospective presentation, reclassified $0.1 and $0.5 million from cost of goods sold and $0.4 and $0.5 million from selling, general and administrative expenses to other income for the three and six months ended June 30, 2017, respectively. In January 2017, the FASB issued ASU No. 2017-04, “Simplifying the Test for Goodwill Impairment (Topic 350).” The update is intended to simplify how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. The amendments in this update are effective for periods beginning after December 15, 2019. Entities are required to apply the amendments in this update prospectively from the date of adoption, with early adoption permitted. The Company adopted this ASU effective January 1, 2018. In August 2016, the FASB issued ASU No. 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments.” The update clarifies how entities should classify certain cash receipts and cash payments on the statement of cash flow. The amendments in this update are effective for periods beginning after December 15, 2017. The Company adopted this ASU effective January 1, 2018. The impact was not material to the Company’s condensed consolidated statement of cash flows. In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842).” ASU 2016-02 requires an entity to recognize a right-of-use asset and lease liability for all leases with terms of more than one year. Recognition, measurement and presentation of expenses will depend on classification as a finance or operating lease. The standard is effective January 1, 2019 and requires a modified retrospective adoption. The Company has a project team analyzing all of its leases to determine the impact that the adoption of ASU 2016-02 will have on its consolidated financial statements. The Company expects this analysis will be completed during the third quarter of 2018. The Company anticipates that it will result in a significant right-of-use asset and related lease liability to be recognized on the Company’s consolidated balance sheet as certain of the Company’s manufacturing facilities, offices and equipment are currently categorized as operating leases.

Plant Closures and Divestitures (Tables)

6 Months Ended

Jun. 30, 2018

Discontinued Operations And Disposal Groups [Abstract]

Summary of Restructuring Activities and Related Reserves

Details of the restructuring activities and related reserves are as follows:

	Severance and employee benefits			Environmental remediation			Site demolition			Other			Total
(Dollars in millions)
Reserve at December 31, 2016	$	1.4		$	1.5		$	10.0		$	3.2		$	16.1
Accrual		0.9			2.1			4.7			6.9			14.6
Cost charged against assets		0.0			0.0			0.0			(6.3	)		(6.3	)
Reversal of accrued charges		(0.3	)		0.0			(1.8	)		0.0			(2.1	)
Cash paid		(0.3	)		(1.1	)		(2.4	)		(1.0	)		(4.8	)
Currency translation		0.0			0.2			0.1			0.5			0.8
Reserve at December 31, 2017	$	1.7		$	2.7		$	10.6		$	3.3		$	18.3
Accrual		0.0			0.9			0.8			2.1			3.8
Cost charged against assets		0.0			0.0			0.0			(2.0	)		(2.0	)
Cash paid		0.0			(2.8	)		(4.2	)		(0.1	)		(7.1	)
Currency translation		0.0			(0.1	)		0.0			0.0			(0.1	)
Reserve at June 30, 2018	$	1.7		$	0.7		$	7.2		$	3.3		$	12.9

Acquisitions (Tables)

6 Months Ended

Jun. 30, 2018

Business Combinations [Abstract]

Summary of Preliminary Valuation of Identifiable Assets Acquired and Liabilities Assumed Upon Acquisition

The preliminary valuation of identifiable assets acquired and liabilities assumed upon the acquisition of UIP and MAER are shown in the table below.

	UIP		MAER
(Dollars in millions)
Cash and cash equivalents	$	1.5	$	3.2
Accounts receivable		20.2		4.9
Inventory		43.1		0.0
Other current assets		1.2		0.3
Property, plant and equipment		19.5		6.6
Intangible assets, net		59.6		19.3
Goodwill		76.0		34.0
Other non-current assets		0.7		0.0
Total assets acquired		221.8		68.3
Accounts payable & accrued expenses		18.4		2.3
Other non-current liabilities		0.5		0.0
Net assets acquired	$	202.9	$	66.0

Schedule of Identifiable Intangible Assets

Net assets acquired included identifiable intangible assets with respect to customer contracts, non-compete agreements and trademarks as summarized in the following table.

	UIP			MAER
(Dollars in millions)	Amount		Remaining Life	Amount		Remaining Life
Customer contracts	$	58.4	15 years	$	18.7	15 years
Non-compete agreements		1.2	5 years
Trademarks					0.6	2 years
Total	$	59.6		$	19.3

Summary of Revenue and Income from Continuing Operations

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
(Dollars in millions)
Pro forma revenue	$	440.3	$	418.2	$	892.8	$	798.9
Pro forma income from continuing operations attributable to Koppers		5.7		21.1		26.6		22.7
Pro forma income per share - continuing operations:
Basic -	$	0.27	$	1.02	$	1.27	$	1.09
Diluted -	$	0.26	$	0.96	$	1.20	$	1.04

Revenue Recognition (Tables)

6 Months Ended

Jun. 30, 2018

Revenue From Contract With Customer [Abstract]

Schedule of Revenue Recognized Net Impact of Adopting Topic 606 Decrease in Sales and Cost of Sales

Revenue recognized during the six months ended June 30, 2018 from the adoption of Topic 606 was $3.3 million and, as such, the net impact of adopting Topic 606 for the three and six months ending June 30, 2018 was a decrease in sales and cost of sales as follows:

	Three Months Ended			Six Months Ended
	June 30,			June 30,
	2018			2018
(Dollars in millions)
Sales	$	(0.7	)	$	(2.0	)
Cost of sales		(0.7	)		(1.9	)

Comprehensive (Loss) Income and Equity (Tables)

6 Months Ended

Jun. 30, 2018

Equity [Abstract]

Schedule of Comprehensive (Loss) Income

Total comprehensive (loss) income for the three and six months ended June 30, 2018 and 2017 is summarized in the table below:

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
(Dollars in millions)
Net income	$	1.0		$	19.8		$	24.7		$	24.4
Other comprehensive (loss) income:
Change in currency translation adjustment		(17.2	)		4.9			(16.0	)		10.9
Unrealized (loss) gain on cash flow hedges, net of tax (benefit) expense of $(2.2), $(0.3), $(6.7) and $0.6		(4.7	)		(0.4	)		(14.0	)		0.9
Change in accounting standard		0.0			0.0			0.3			0.0
Unrecognized pension net loss, net of tax expense of $0.1, $0.2, $0.2 and $0.4		0.2			0.4			0.5			0.7
Total comprehensive (loss) income		(20.7	)		24.7			(4.5	)		36.9
Less: Comprehensive (loss) income attributable to noncontrolling interests		(0.3	)		0.2			5.8			0.4
Comprehensive (loss) income attributable to Koppers	$	(20.4	)	$	24.5		$	(10.3	)	$	36.5

Schedule of Change in Equity

The following tables present the change in equity for the six months ended June 30, 2018 and 2017, respectively:

(Dollars in millions)	Total Koppers Shareholders’ Equity			Noncontrolling Interests			Total Equity
Balance at December 31, 2017	$	99.9		$	5.9		$	105.8
Net income		18.4			6.3			24.7
Issuance of common stock		2.2			0.0			2.2
Employee stock plans		6.0			0.0			6.0
Other comprehensive loss		(28.7	)		(0.5	)		(29.2	)
Repurchases of common stock		(7.4	)		0.0			(7.4	)
Balance at June 30, 2018	$	90.4		$	11.7		$	102.1

(Dollars in millions)	Total Koppers Shareholders’ Equity			Noncontrolling Interests		Total Equity
Balance at December 31, 2016	$	30.4		$	4.2	$	34.6
Net income		24.1			0.3		24.4
Issuance of common stock		1.9			0.0		1.9
Employee stock plans		5.3			0.0		5.3
Other comprehensive income		12.4			0.1		12.5
Repurchases of common stock		(5.2	)		0.0		(5.2	)
Balance at June 30, 2017	$	68.9		$	4.6	$	73.5

Earnings per Common Share (Tables)

6 Months Ended

Jun. 30, 2018

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:

	Three Months Ended June 30,					Six Months Ended June 30,
	2018		2017			2018		2017
(Dollars in millions, except share amounts, in thousands, and per share amounts)
Net income attributable to Koppers	$	0.6	$	19.7		$	18.4	$	24.1
Less: Income (loss) from discontinued operations		0.5		(1.1	)		0.4		(1.2	)
Income from continuing operations attributable to Koppers	$	0.1	$	20.8		$	18.0	$	25.3
Weighted average common shares outstanding:
Basic		21,138		20,782			21,016		20,752
Effect of dilutive securities		916		1,101			1,076		1,146
Diluted		22,054		21,883			22,092		21,898
Income per common share – continuing operations:
Basic income per common share	$	0.01	$	1.00		$	0.86	$	1.22
Diluted income per common share		0.01		0.95			0.81		1.15
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share		249		509			195		344

Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

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

Stock Options And Performance Award Fair Value Assumptions

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

	May 2018 Grant			March 2018 Grant			March 2017 Grant			March 2016 Grant			March 2015 Grant
Grant date price per share	$	39.10		$	41.60		$	44.10		$	18.11		$	17.57
Expected dividend yield per share		0.00	%		0.00	%		0.00	%		0.00	%		3.40	%
Expected life in years		5.73			5.73			5.77			5.96			5.75
Expected volatility		37.05	%		37.05	%		39.70	%		40.86	%		42.27	%
Risk-free interest rate		2.82	%		2.67	%		2.13	%		1.45	%		1.73	%
Grant date fair value per share	$	15.48		$	16.38		$	17.90		$	7.41		$	5.20

Summary of Performance Stock Units

The following table shows a summary of the performance stock units as of June 30, 2018:

Performance Period	Minimum Shares		Target Shares		Maximum Shares
2016 – 2018		0		255,172		510,344
2017 – 2019		0		113,675		227,350
2018 – 2020		0		130,782		261,564

Summary of Status and Activity of Non-Vested Stock Units

The following table shows a summary of the status and activity of non-vested stock units for the six months ended June 30, 2018:

	Restricted Stock Units			Performance Stock Units			Total Stock Units			Weighted Average Grant Date Fair Value per Unit
Non-vested at December 31, 2017		238,140			581,551			819,691		$	29.14
Granted		110,743			134,351			245,094		$	44.18
Performance share adjustment		0			204,866			204,866		$	17.57
Vested		(92,089	)		(409,732	)		(501,821	)	$	19.35
Forfeited		(7,094	)		(11,407	)		(18,501	)	$	38.77
Non-vested at June 30, 2018		249,700			499,629			749,329		$	37.20

Summary of Status and Activity of Stock Options

The following table shows a summary of the status and activity of stock options for the six months ended June 30, 2018:

	Options			Weighted Average Exercise Price per Option		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2017		942,537		$	27.59
Granted		144,825		$	41.50
Exercised		(65,897	)	$	28.59
Forfeited		(12,329	)	$	30.49
Outstanding at June 30, 2018		1,009,136		$	29.48		6.37	$	10.4
Exercisable at June 30, 2018		621,771		$	28.40		5.11	$	6.7

Schedule of Stock-based Compensation Expense Recognized

Stock Compensation Expense

Total stock-based compensation expense recognized under the Company’s LTIP and employee stock purchase plan for three and six months ended June 30, 2018 and 2017 is as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
(Dollars in millions)
Stock-based compensation expense recognized:
Selling, general and administrative expenses	$	3.1	$	2.7	$	6.0	$	5.0
Less related income tax benefit		1.0		0.7		1.9		1.2
Decrease in net income attributable to Koppers	$	2.1	$	2.0	$	4.1	$	3.8
Intrinsic value of exercised stock options	$	0.8	$	0.3	$	1.0	$	1.1
Cash received from the exercise of stock options	$	0.9	$	0.3	$	2.2	$	1.9

Performance Stock Units [Member]

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

Stock Options And Performance Award Fair Value Assumptions

The Company calculated the fair value of the awards on the date of grant using the Monte Carlo valuation model and the assumptions listed below:

	May 2018 Grant			March 2018 Grant			March 2017 Grant			March 2016 Grant
Grant date price per share	$	39.10		$	41.60		$	44.10		$	18.11
Expected dividend yield per share		0.00	%		0.00	%		0.00	%		0.00	%
Expected volatility		39.40	%		39.40	%		43.50	%		40.86	%
Risk-free interest rate		2.35	%		2.35	%		1.54	%		0.96	%
Look-back period in years		2.84			2.84			2.83			2.84
Grant date fair value per share	$	44.29		$	47.12		$	64.02		$	23.70

Segment Information (Tables)

6 Months Ended

Jun. 30, 2018

Segment Reporting [Abstract]

Summary of Results of Segment Operations

The following table sets forth certain sales and operating data, net of all intersegment transactions, for the Company’s segments for the periods indicated:

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
(Dollars in millions)
Revenues from external customers:
Railroad and Utility Products and Services	$	177.2		$	135.9		$	285.6		$	271.4
Performance Chemicals		115.1			111.8			212.5			208.5
Carbon Materials and Chemicals		143.7			130.3			344.0			244.7
Total	$	436.0		$	378.0		$	842.1		$	724.6
Intersegment revenues:
Performance Chemicals	$	2.4		$	1.5		$	4.2		$	3.2
Carbon Materials and Chemicals		19.2			19.0			37.4			37.9
Total	$	21.6		$	20.5		$	41.6		$	41.1
Depreciation and amortization expense:
Railroad and Utility Products and Services	$	4.9		$	2.9		$	7.9		$	5.9
Performance Chemicals		4.5			4.5			8.9			8.9
Carbon Materials and Chemicals		4.3			4.3			8.7			8.1
Total	$	13.7		$	11.7		$	25.5		$	22.9
Operating profit (loss):
Railroad and Utility Products and Services^(a)	$	(1.0	)	$	11.3		$	0.1		$	20.6
Performance Chemicals		11.6			19.6			17.2			38.2
Carbon Materials and Chemicals		12.5			8.0			49.7			8.6
Corporate^(b)		(0.8	)		(0.8	)		(1.4	)		(1.2	)
Total	$	22.3		$	38.1		$	65.6		$	66.2

(a)

Operating loss for the three and six months ended June 30, 2018 includes $5.5 million of inventory fair value purchase price adjustment related to the Company’s UIP acquisition.

(b)

Operating loss for Corporate includes primarily general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc.

Schedule of Segment Revenues for Significant Product Lines

The following table sets forth revenues for significant product lines, net of all intersegment transactions, for the Company’s segments for the periods indicated:

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
(Dollars in millions)
Railroad and Utility Products and Services:
Railroad treated products	$	88.0	$	101.1	$	163.1	$	203.8
Utility poles		58.9		10.4		70.4		21.2
Rail joints		9.7		7.6		18.1		15.0
Railroad infrastructure services		9.1		9.3		16.1		17.9
Other products		11.5		7.5		17.9		13.5
		177.2		135.9		285.6		271.4
Performance Chemicals:
Wood preservative products		112.8		109.1		208.1		203.6
Other products		2.3		2.7		4.4		4.9
		115.1		111.8		212.5		208.5
Carbon Materials and Chemicals:
Pitch and related products		86.0		68.6		215.2		116.8
Creosote and distillates		19.3		19.0		42.2		39.5
Phthalic anhydride and other chemicals		18.4		21.6		40.6		44.8
Naphthalene		9.6		8.8		22.7		17.9
Other products		10.4		12.2		23.3		25.8
		143.7		130.3		344.0		244.7
Total	$	436.0	$	378.0	$	842.1	$	724.6

Summary of Tangible and Intangible Assets by Segments

The following table sets forth certain tangible and intangible assets allocated to each of the Company’s segments as of the dates indicated:

	June 30, 2018		December 31, 2017
(Dollars in millions)
Segment assets:
Railroad and Utility Products and Services	$	551.9	$	249.7
Performance Chemicals		486.7		494.0
Carbon Materials and Chemicals		454.8		414.2
All other		38.3		42.3
Total	$	1,531.7	$	1,200.2
Goodwill:
Railroad and Utility Products and Services^(a)	$	120.2	$	10.5
Performance Chemicals		176.1		177.7
Total	$	296.4	$	188.2

(a)

The increase in goodwill as of June 30, 2018 includes $110.1 million attributable to the Company’s acquisitions of UIP and MAER during 2018.

Income Taxes (Tables)

6 Months Ended

Jun. 30, 2018

Income Tax Disclosure [Abstract]

Summary of Income Taxes Reconciled with Federal Statutory Rate

The estimated annual effective income tax rate differs from the U.S. federal statutory tax rate due to:

	Six Months Ended June 30,			Six Months Ended June 30,
	2018			2017
Federal income tax rate		21.0	%		35.0	%
State income taxes, net of federal tax benefit		0.3			2.1
Foreign earnings taxed at different rates		4.3			(15.7	)
GILTI inclusion (net of foreign tax credits)		10.2			0.0
Valuation allowance adjustments		(7.8	)		0.0
Interest expense deduction limitation		2.0			0.0
Nondeductible expenses		1.8			2.1
Change in tax contingency reserves		0.1			0.3
Other		0.4			0.8
Estimated annual effective income tax rate		32.3	%		24.6	%

Inventories (Tables)

6 Months Ended

Jun. 30, 2018

Inventory Disclosure [Abstract]

Components of Inventories

Net inventories as of June 30, 2018 and December 31, 2017 are summarized in the table below:

	June 30, 2018		December 31, 2017
(Dollars in millions)
Raw materials	$	209.7	$	173.6
Work in process		14.0		11.2
Finished goods		123.1		98.4
	$	346.8	$	283.2
Less revaluation to LIFO		50.9		46.3
Net	$	295.9	$	236.9

Property, Plant and Equipment (Tables)

6 Months Ended

Jun. 30, 2018

Property Plant And Equipment [Abstract]

Property, Plant and Equipment

Property, plant and equipment as of June 30, 2018 and December 31, 2017 are summarized in the table below:

	June 30, 2018		December 31, 2017
(Dollars in millions)
Land	$	17.1	$	17.6
Buildings		63.4		63.4
Machinery and equipment		822.4		756.6
	$	902.9	$	837.6
Less accumulated depreciation		518.4		509.6
Net	$	384.5	$	328.0

Pensions and Post-Retirement Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2018

Compensation And Retirement Disclosure [Abstract]

Components of Net Periodic Benefit Cost for Pension Plans

The following table provides the components of net periodic benefit cost for the pension plans for the three and six months ended June 30, 2018 and 2017:

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
(Dollars in millions)
Service cost	$	0.4		$	0.5		$	0.9		$	1.0
Interest cost		2.0			2.5			3.8			4.9
Expected return on plan assets		(2.2	)		(2.5	)		(4.3	)		(5.0	)
Amortization of net loss		0.3			0.5			0.7			1.0
Net periodic benefit cost	$	0.5		$	1.0		$	1.1		$	1.9
Defined contribution plan expense	$	2.2		$	1.8		$	4.2		$	4.0

Debt (Tables)

6 Months Ended

Jun. 30, 2018

Schedule of Long-Term Debt Instruments

Debt as of June 30, 2018 and December 31, 2017 was as follows:

	Weighted Average Interest Rate			Maturity	June 30, 2018		December 31, 2017
(Dollars in millions)
Term Loan		5.12	%	2023	$	97.5	$	0.0
Revolving Credit Facility		5.12	%	2023		390.1		155.0
Construction and other loans		4.69	%	2020		25.9		33.7
Senior Notes due 2025		6.00	%	2025		500.0		500.0
Debt						1,013.5		688.7
Less short-term debt and current maturities of long-term debt						15.3		11.4
Less unamortized debt issuance costs						13.4		11.7
Long-term debt					$	984.8	$	665.6

- 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

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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
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-Topic 835
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 505
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-Subparagraph (SX 210.4-08.(e),(f))
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Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 835
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-Section 55
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Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 505
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+ Details

Asset Retirement Obligations (Tables)

6 Months Ended

Jun. 30, 2018

Asset Retirement Obligation Disclosure [Abstract]

Schedule of Changes in Carrying Values of Asset Retirement Obligations

The following table reflects changes in the carrying values of asset retirement obligations:

	June 30, 2018			December 31, 2017
(Dollars in millions)
Asset retirement obligation at beginning of year	$	37.1		$	36.0
Accretion expense		0.8			2.4
Revision in estimated cash flows		0.7			9.4
Cash expenditures		(5.7	)		(10.9	)
Currency translation		0.0			0.2
Balance at end of period	$	32.9		$	37.1

Deferred Revenue (Tables)

6 Months Ended

Jun. 30, 2018

Deferred Revenue Disclosure [Abstract]

Deferred Revenue from Extended Product Warranty Liabilities

The following table reflects changes in the carrying values of deferred revenue:

	June 30, 2018			December 31, 2017
(Dollars in millions)
Balance at beginning of year	$	28.1		$	27.2
Revenue earned		(0.3	)		(0.7	)
Currency translation		(0.5	)		1.6
Balance at end of period	$	27.3		$	28.1

Derivative Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2018

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Schedule of Outstanding Copper Swap Contracts

As of June 30, 2018 and December 31, 2017, the Company had outstanding copper swap contracts of the following amounts:

	Units Outstanding (in Pounds)		Net Fair Value - Asset
	June 30, 2018	December 31, 2017	June 30, 2018		December 31, 2017
(Amounts in millions)
Cash flow hedges	35.2	37.8	$	8.3	$	25.5
Not designated as hedges	10.1	11.3		0.1		4.5
Total	45.3	49.1	$	8.4	$	30.0

Schedule of Fair Value of Outstanding Copper Swap Contracts Recorded in Balance Sheet

As of June 30, 2018 and December 31, 2017, the fair value of the outstanding copper swap contracts is recorded in the balance sheet as follows:

	June 30, 2018			December 31, 2017
(Dollars in millions)
Other current assets	$	6.5		$	21.8
Other assets		2.0			8.2
Accrued liabilities		(0.1	)		0.0
Net asset on balance sheet	$	8.4		$	30.0
Accumulated other comprehensive gain, net of tax	$	6.2		$	15.8

Summary of Amount Recognized in Earnings Related to Copper Swap Contracts

	Three Months Ended June 30,					Six Months Ended June 30,
	2018			2017		2018			2017
(Dollars in millions)
Gain from ineffectiveness of cash flow hedges	$	0.0		$	1.1	$	0.0		$	3.0
(Loss) gain from contracts not designated as hedges		(1.0	)		0.3		(4.5	)		1.0
Net	$	(1.0	)	$	1.4	$	(4.5	)	$	4.0

Summary of Net Currency Units Outstanding

As of June 30, 2018 and December 31, 2017, the net currency units outstanding for these contracts were:

	June 30, 2018		December 31, 2017
(In millions)
British Pounds		GBP 6.2		GBP 7.0
New Zealand Dollars		NZD 16.0		NZD 15.5
United States Dollars		USD 1.4		USD 12.5
Canadian Dollars		CAD 2.5		CAD 2.5
Euro		EUR 0.3		EUR 0.0

Commitments and Contingent Liabilities (Tables)

6 Months Ended

Jun. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Changes in Accrued Liability for Environmental Matters

The following table reflects changes in the accrued liability for environmental matters, of which $4.5 million and $5.1 million are classified as current liabilities at June 30, 2018 and December 31, 2017, respectively:

	Period ended
	June 30, 2018			December 31, 2017
(Dollars in millions)
Balance at beginning of year	$	13.9		$	12.9
Expense		1.0			3.2
Reversal of reserves		0.0			(0.7	)
Cash expenditures		(2.9	)		(1.8	)
Acquisition		1.9			0.0
Currency translation		(0.3	)		0.3
Balance at end of period	$	13.6		$	13.9

Subsidiary Guarantor Information for Koppers Inc. Shelf Registration (Tables)

6 Months Ended

Jun. 30, 2018

Condensed Consolidating Statement of Operations

For the Three Months Ended June 30, 2018

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Net sales	$	0.0		$	140.2		$	95.9	$	218.8		$	(18.9	)	$	436.0
Cost of sales including depreciation and amortization		0.0			129.3			72.1		186.6			(20.1	)		367.9
Selling, general and administrative		0.8			15.2			11.9		17.9			0.0			45.8
Operating profit (loss)		(0.8	)		(4.3	)		11.9		14.3			1.2			22.3
Other (loss) income		0.0			(2.4	)		0.4		1.3			0.0			(0.7	)
Equity income (loss) of subsidiaries		1.2			21.9			16.3		(0.1	)		(39.3	)		0.0
Interest expense		0.0			13.9			0.0		0.6			0.0			14.5
Income taxes		(0.2	)		0.1			2.7		4.0			0.0			6.6
Income from continuing operations		0.6			1.2			25.9		10.9			(38.1	)		0.5
Discontinued operations		0.0			0.0			0.0		0.5			0.0			0.5
Noncontrolling interests		0.0			0.0			0.0		0.4			0.0			0.4
Net income attributable to Koppers	$	0.6		$	1.2		$	25.9	$	11.0		$	(38.1	)	$	0.6
Comprehensive income attributable to Koppers	$	(20.4	)	$	(20.0	)	$	4.7	$	(5.9	)	$	21.2		$	(20.4	)

Condensed Consolidating Statement of Operations

For the Three Months Ended June 30, 2017

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Net sales	$	0.0		$	153.2		$	94.2		$	151.8		$	(21.2	)	$	378.0
Cost of sales including depreciation and amortization		0.0			141.8			65.1			123.0			(21.5	)		308.4
Selling, general and administrative		0.5			10.9			10.1			10.0			0.0			31.5
Operating profit (loss)		(0.5	)		0.5			19.0			18.8			0.3			38.1
Other income (loss)		0.0			(0.4	)		0.6			0.3			(0.3	)		0.2
Equity income (loss) of subsidiaries		20.0			25.5			12.9			(0.1	)		(58.3	)		0.0
Interest expense		0.0			10.0			(0.1	)		1.2			(0.3	)		10.8
Loss on extinguishment of debt		0.0			0.0			0.0			0.0			0.0			0.0
Income taxes		(0.2	)		(4.4	)		7.2			4.0			0.0			6.6
Income (loss) from continuing operations		19.7			20.0			25.4			13.8			(58.0	)		20.9
Discontinued operations		0.0			0.0			0.0			(1.1	)		0.0			(1.1	)
Noncontrolling interests		0.0			0.0			0.0			0.1			0.0			0.1
Net income attributable to Koppers	$	19.7		$	20.0		$	25.4		$	12.6		$	(58.0	)	$	19.7
Comprehensive income (loss) attributable to Koppers	$	24.5		$	24.8		$	29.9		$	18.5		$	(73.2	)	$	24.5

Condensed Consolidating Statement of Operations

For the Six Months Ended June 30, 2018

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Net sales	$	0.0		$	271.3		$	173.4	$	434.5		$	(37.1	)	$	842.1
Cost of sales including depreciation and amortization		0.0			252.2			134.4		344.3			(38.3	)		692.6
Selling, general and administrative		1.4			27.3			23.9		31.3			0.0			83.9
Operating profit (loss)		(1.4	)		(8.2	)		15.1		58.9			1.2			65.6
Other (loss) income		0.0			(2.8	)		0.8		1.5			0.0			(0.5	)
Equity income (loss) of subsidiaries		19.5			58.4			49.9		(0.1	)		(127.7	)		0.0
Interest expense		0.0			23.8			0.0		1.2			0.0			25.0
Income taxes		(0.3	)		4.1			3.6		8.4			0.0			15.8
Income from continuing operations		18.4			19.5			62.2		50.7			(126.5	)		24.3
Discontinued operations		0.0			0.0			0.0		0.4			0.0			0.4
Noncontrolling interests		0.0			0.0			0.0		6.3			0.0			6.3
Net income attributable to Koppers	$	18.4		$	19.5		$	62.2	$	44.8		$	(126.5	)	$	18.4
Comprehensive income attributable to Koppers	$	(10.3	)	$	(9.4	)	$	32.7	$	28.7		$	(52.0	)	$	(10.3	)

Condensed Consolidating Statement of Operations

For the Six Months Ended June 30, 2017

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Net sales	$	0.0		$	304.1		$	175.4	$	288.2		$	(43.1	)	$	724.6
Cost of sales including depreciation and amortization		0.0			289.5			119.1		228.8			(41.4	)		596.0
Selling, general and administrative		1.0			21.7			20.3		19.4			0.0			62.4
Operating profit (loss)		(1.0	)		(7.1	)		36.0		40.0			(1.7	)		66.2
Other income		0.0			(0.8	)		1.2		1.8			(0.5	)		1.7
Equity income of subsidiaries		24.9			51.8			30.3		(0.1	)		(106.9	)		0.0
Interest expense		0.0			19.7			0.0		2.1			(0.4	)		21.4
Loss on extinguishment of debt		0.0			13.3			0.0		0.0			0.0			13.3
Income taxes		(0.2	)		(14.0	)		13.7		8.1			0.0			7.6
Income from continuing operations		24.1			24.9			53.8		31.5			(108.7	)		25.6
Discontinued operations		0.0			0.0			0.0		(1.2	)		0.0			(1.2	)
Noncontrolling interests		0.0			0.0			0.0		0.3			0.0			0.3
Net income attributable to Koppers	$	24.1		$	24.9		$	53.8	$	30.0		$	(108.7	)	$	24.1
Comprehensive income attributable to Koppers	$	36.5		$	37.4		$	65.8	$	42.0		$	(145.2	)	$	36.5

Condensed Consolidating Balance Sheet

June 30, 2018

	Parent		Koppers Inc.		Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries		Consolidating Adjustments			Consolidated
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0.0	$	0.3	$	0.1		$	62.1	$	0.0		$	62.5
Receivables, net		0.0		61.1		39.0			117.6		0.0			217.7
Affiliated receivables		1.1		12.8		8.7			6.4		(29.0	)		0.0
Inventories, net		0.0		100.5		45.7			150.5		(0.8	)		295.9
Other current assets		0.0		6.4		8.3			18.1		0.4			33.2
Total current assets		1.1		181.1		101.8			354.7		(29.4	)		609.3
Equity investments		89.4		1,014.1		310.4			0.1		(1,414.0	)		0.0
Property, plant and equipment, net		0.0		190.4		46.7			147.4		0.0			384.5
Goodwill		0.0		0.8		153.1			142.5		0.0			296.4
Intangible assets, net		0.0		7.0		94.1			97.6		0.0			198.7
Deferred tax assets		0.0		24.4		(9.1	)		2.8		0.0			18.1
Affiliated loan receivables		0.0		41.4		149.2			7.7		(198.3	)		0.0
Other assets		0.0		4.7		6.2			13.8		0.0			24.7
Total assets	$	90.5	$	1,463.9	$	852.4		$	766.6	$	(1,641.7	)	$	1,531.7
LIABILITIES AND EQUITY
Accounts payable		0.0		79.9		40.9			53.6		0.0			174.4
Affiliated payables		0.0		19.3		2.5			8.0		(29.8	)		0.0
Accrued liabilities		0.0		53.5		16.5			40.0		0.0			110.0
Current maturities of long-term debt		0.0		10.1		0.1			5.1		0.0			15.3
Total current liabilities		0.0		162.8		60.0			106.7		(29.8	)		299.7
Long-term debt		0.0		964.1		0.2			20.5		0.0			984.8
Affiliated debt		0.0		156.1		33.1			9.1		(198.3	)		0.0
Other long-term liabilities		0.0		90.8		14.1			40.2		0.0			145.1
Total liabilities		0.0		1,373.8		107.4			176.5		(228.1	)		1,429.6
Koppers shareholders’ equity		90.5		90.1		745.0			578.4		(1,413.6	)		90.4
Noncontrolling interests		0.0		0.0		0.0			11.7		0.0			11.7
Total liabilities and equity	$	90.5	$	1,463.9	$	852.4		$	766.6	$	(1,641.7	)	$	1,531.7

Condensed Consolidating Balance Sheet

December 31, 2017

	Parent		Koppers Inc.			Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0.0	$	0.7		$	0.0		$	59.6		$	0.0		$	60.3
Receivables, net		0.0		48.6			27.7			84.6			0.0			160.9
Affiliated receivables		0.6		19.4			(83.0	)		(12.1	)		75.1			0.0
Inventories, net		0.0		80.4			40.5			117.9			(1.9	)		236.9
Deferred tax assets		0.0		0.0			0.0			(0.1	)		0.1			0.0
Other current assets		0.0		6.6			23.0			18.8			0.2			48.6
Total current assets		0.6		155.7			8.2			268.7			73.5			506.7
Equity investments		99.3		716.3			276.8			(0.1	)		(1,092.3	)		0.0
Property, plant and equipment, net		0.0		155.2			47.3			125.5			0.0			328.0
Goodwill		0.0		0.8			153.1			34.3			0.0			188.2
Intangible assets, net		0.0		7.2			96.7			25.7			0.0			129.6
Deferred tax assets		0.0		29.4			(13.2	)		2.2			0.0			18.4
Affiliated loan receivables		0.0		34.9			224.3			21.4			(280.6	)		0.0
Other assets		0.0		4.4			15.3			9.6			0.0			29.3
Total assets	$	99.9	$	1,103.9		$	808.5		$	487.3		$	(1,299.4	)	$	1,200.2
LIABILITIES AND EQUITY
Accounts payable	$	0.0	$	65.1		$	32.4		$	44.4		$	0.0		$	141.9
Affiliated payables		0.0		(90.3	)		13.8			2.2			74.3			0.0
Accrued liabilities		0.0		59.9			16.4			51.6			0.0			127.9
Current maturities of long-term debt		0.0		0.1			0.0			11.3			0.0			11.4
Total current liabilities		0.0		34.8			62.6			109.5			74.3			281.2
Long-term debt		0.0		643.3			0.0			22.3			0.0			665.6
Affiliated debt		0.0		233.7			19.3			27.6			(280.6	)		0.0
Other long-term liabilities		0.0		92.0			14.4			41.2			0.0			147.6
Total liabilities		0.0		1,003.8			96.3			200.6			(206.3	)		1,094.4
Koppers shareholders’ equity		99.9		100.1			712.2			280.8			(1,093.1	)		99.9
Noncontrolling interests		0.0		0.0			0.0			5.9			0.0			5.9
Total liabilities and equity	$	99.9	$	1,103.9		$	808.5		$	487.3		$	(1,299.4	)	$	1,200.2

Condensed Consolidating Statement of Cash Flows

For the Six Months Ended June 30, 2018

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Cash provided by (used in) operating activities	$	5.3		$	(34.0	)	$	9.7		$	29.5		$	(7.4	)	$	3.1
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0.0			(307.8	)		(1.9	)		(8.0	)		0.0			(317.7	)
Repayments (loans to) from affiliates		0.0			(0.4	)		(8.2	)		(3.7	)		12.3			0.0
Insurance proceeds received		0.0			0.0			0.0			0.7			0.0			0.7
Net cash provided by divestitures and asset sales		0.0			(2.1	)		0.0			3.6			0.0			1.5
Net cash (used in) provided by investing activities		0.0			(310.3	)		(10.1	)		(7.4	)		12.3			(315.5	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0.0			332.4			0.0			(7.7	)		0.0			324.7
Borrowings (repayments) of affiliated debt		0.0			21.8			0.5			(10.0	)		(12.3	)		0.0
Debt issuance costs		0.0			(2.9	)		0.0			0.0			0.0			(2.9	)
Dividends paid		0.0			(7.4	)		0.0			0.0			7.4			0.0
Stock repurchased		(5.3	)		0.0			0.0			0.1			0.0			(5.2	)
Net cash provided by (used in) financing activities		(5.3	)		343.9			0.5			(17.6	)		(4.9	)		316.6
Effect of exchange rates on cash		0.0			0.0			0.0			(2.0	)		0.0			(2.0	)
Net increase in cash and cash equivalents		0.0			(0.4	)		0.1			2.5			0.0			2.2
Cash and cash equivalents at beginning of year		0.0			0.7			0.0			59.6			0.0			60.3
Cash and cash equivalents at end of period	$	0.0		$	0.3		$	0.1		$	62.1		$	0.0		$	62.5

Condensed Consolidating Statement of Cash Flows

For the Six Months Ended June 30, 2017

	Parent			Koppers Inc.			Domestic Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Consolidating Adjustments			Consolidated
(Dollars in millions)
Cash provided by (used in) operating activities	$	3.3		$	(8.4	)	$	26.4		$	12.0		$	(2.0	)	$	31.3
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0.0			(23.1	)		(8.0	)		(3.1	)		0.0			(34.2	)
Repayments (loans to) from affiliates		0.0			2.9			(12.5	)		0.7			8.9			0.0
Repayment of loan		0.0			0.0			0.0			9.5			0.0			9.5
Net cash proceeds from divestitures and asset sales		0.0			0.0			0.5			0.3			0.0			0.8
Net cash (used in) provided by investing activities		0.0			(20.2	)		(20.0	)		7.4			8.9			(23.9	)
Cash provided by (used in) financing activities:
Repayments of long-term debt		0.0			30.0			0.0			(4.0	)		0.0			26.0
Borrowings (repayments) of affiliated debt		0.0			11.6			(6.4	)		3.7			(8.9	)		0.0
Deferred financing cost		0.0			(11.0	)		0.0			0.0			0.0			(11.0	)
Dividends paid		0.0			(2.0	)		0.0			0.0			2.0			0.0
Stock repurchased		(3.3	)		0.0			0.0			0.0			0.0			(3.3	)
Net cash provided by (used in) financing activities		(3.3	)		28.6			(6.4	)		(0.3	)		(6.9	)		11.7
Effect of exchange rates on cash		0.0			0.0			0.0			0.1			0.0			0.1
Net decrease in cash and cash equivalents		0.0			0.0			0.0			19.2			0.0			19.2
Cash and cash equivalents at beginning of year		0.0			0.0			0.0			20.8			0.0			20.8
Cash and cash equivalents at end of period	$	0.0		$	0.0		$	0.0		$	40.0		$	0.0		$	40.0

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of Company's Financial Instruments

Carrying amounts and the related estimated fair values of the Company’s financial instruments as of June 30, 2018 and December 31, 2017 are as follows:

	June 30, 2018				December 31, 2017
	Fair Value		Carrying Value		Fair Value		Carrying Value
(Dollars in millions)
Financial assets:
Cash and cash equivalents, including restricted cash	$	62.5	$	62.5	$	60.3	$	60.3
Investments and other assets^(a)		1.1		1.1		1.1		1.1
Financial liabilities:
Long-term debt (including current portion)	$	1,003.5	$	1,013.5	$	706.9	$	688.7

(a)	Excludes equity method investments.

New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Summary Of Significant Accounting Policies [Line Items]
Cost of goods sold	$ (352.8)	$ (294.6)	$ (664.2)	$ (569.5)
Selling, general and administrative expenses	$ (45.8)	(31.5)	(83.9)	(62.4)
ASU No. 2017-12 [Member]
Summary Of Significant Accounting Policies [Line Items]
Reclassification of unrealized gain from retained earnings to accumulated other comprehensive loss			$ 3.6
ASU No. 2017-07 [Member] \| Scenario, Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Cost of goods sold		0.1		0.5
Selling, general and administrative expenses		$ 0.4		$ 0.5

Plant Closures and Divestitures - Additional Information (Detail)	Dec. 31, 2016	Nov. 30, 2016	Mar. 31, 2016	Jul. 31, 2015
Discontinued Operations Disposed Of By Means Other Than Sale [Member] \| China [Member] \| Carbon Materials and Chemicals [Member]
Restructuring Cost and Reserve [Line Items]
Percentage of operations in Tangshan, China owned by the company			60.00%
Tangshan Koppers Kailuan Carbon Chemical Company Limited [Member]
Restructuring Cost and Reserve [Line Items]
Ownership percentage	30.00%	30.00%
KSA Limited Partnership [Member]
Restructuring Cost and Reserve [Line Items]
Ownership percentage				50.00%

Plant Closures and Divestitures - Summary of Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	$ 18.3	$ 16.1
Accrual	3.8	14.6
Cost charged against assets	(2.0)	(6.3)
Reversal of accrued charges		(2.1)
Cash paid	(7.1)	(4.8)
Currency translation	(0.1)	0.8
Reserve, Ending Balance	12.9	18.3
Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	2.7	1.5
Accrual	0.9	2.1
Cost charged against assets	0.0	0.0
Reversal of accrued charges		0.0
Cash paid	(2.8)	(1.1)
Currency translation	(0.1)	0.2
Reserve, Ending Balance	0.7	2.7
Severance and Employee Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	1.7	1.4
Accrual	0.0	0.9
Cost charged against assets	0.0	0.0
Reversal of accrued charges		(0.3)
Cash paid	0.0	(0.3)
Currency translation	0.0	0.0
Reserve, Ending Balance	1.7	1.7
Site Demolition [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	10.6	10.0
Accrual	0.8	4.7
Cost charged against assets	0.0	0.0
Reversal of accrued charges		(1.8)
Cash paid	(4.2)	(2.4)
Currency translation	0.0	0.1
Reserve, Ending Balance	7.2	10.6
Other [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	3.3	3.2
Accrual	2.1	6.9
Cost charged against assets	(2.0)	(6.3)
Reversal of accrued charges		0.0
Cash paid	(0.1)	(1.0)
Currency translation	0.0	0.5
Reserve, Ending Balance	$ 3.3	$ 3.3

Acquisitions - Additional Information (Detail) $ in Millions			3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 10, 2018 USD ($) Facility Yard	Feb. 28, 2018 USD ($) Facility	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Combined costs related to acquisitions			$ 3.5		$ 5.6
Net sales			436.0	$ 378.0	842.1	$ 724.6
Loss before taxes			$ (7.1)	$ (27.5)	(40.1)	$ (33.2)
Koppers Utility and Industrial Products Inc. [Member]
Business Acquisition [Line Items]
Cash consideration	$ 201.4
Number of manufacturing facilities \| Facility	8
Number of distribution yards \| Yard	19
Revenues	$ 147.0
Net sales					46.4
Loss before taxes					4.3
Inventory fair value purchase price accounting adjustments					$ 5.5
M.A. Energy Resources, LLC [Member]
Business Acquisition [Line Items]
Cash consideration		$ 62.8
Revenues							$ 30.0
Number of processing facilities \| Facility		2

Acquisitions - Summary of Preliminary Valuation of Identifiable Assets Acquired and Liabilities Assumed Upon Acquisition (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Apr. 10, 2018	Feb. 28, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 296.4			$ 188.2
Koppers Utility and Industrial Products Inc. [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		$ 1.5
Accounts receivable		20.2
Inventory		43.1
Other current assets		1.2
Property, plant and equipment		19.5
Intangible assets, net		59.6
Goodwill		76.0
Other non-current assets		0.7
Total assets acquired		221.8
Accounts payable & accrued expenses		18.4
Other non-current liabilities		0.5
Net assets acquired		$ 202.9
M.A. Energy Resources, LLC [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			$ 3.2
Accounts receivable			4.9
Inventory			0.0
Other current assets			0.3
Property, plant and equipment			6.6
Intangible assets, net			19.3
Goodwill			34.0
Other non-current assets			0.0
Total assets acquired			68.3
Accounts payable & accrued expenses			2.3
Other non-current liabilities			0.0
Net assets acquired			$ 66.0

Acquisitions - Schedule of Identifiable Intangible Assets (Detail) - USD ($) $ in Millions	Apr. 10, 2018	Feb. 28, 2018
Koppers Utility and Industrial Products Inc. [Member]
Business Acquisition [Line Items]
Amount	$ 59.6
M.A. Energy Resources, LLC [Member]
Business Acquisition [Line Items]
Amount		$ 19.3
Customer Contracts [Member] \| Koppers Utility and Industrial Products Inc. [Member]
Business Acquisition [Line Items]
Amount	$ 58.4
Remaining Life	15 years
Customer Contracts [Member] \| M.A. Energy Resources, LLC [Member]
Business Acquisition [Line Items]
Amount		$ 18.7
Remaining Life		15 years
Non-Compete Agreements [Member] \| Koppers Utility and Industrial Products Inc. [Member]
Business Acquisition [Line Items]
Amount	$ 1.2
Remaining Life	5 years
Trademarks [Member] \| M.A. Energy Resources, LLC [Member]
Business Acquisition [Line Items]
Amount		$ 0.6
Remaining Life		2 years

Acquisitions - Summary of Revenue and Income from Continuing Operations (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Combinations [Abstract]
Pro forma revenue	$ 440.3	$ 418.2	$ 892.8	$ 798.9
Pro forma income from continuing operations attributable to Koppers	$ 5.7	$ 21.1	$ 26.6	$ 22.7
Pro forma income per share - continuing operations, Basic	$ 0.27	$ 1.02	$ 1.27	$ 1.09
Pro forma income per share - continuing operations, Diluted	$ 0.26	$ 0.96	$ 1.20	$ 1.04

Revenue Recognition - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Disaggregation Of Revenue [Line Items]
Effect on revenue	$ 436.0	$ 378.0	$ 842.1	$ 724.6
Accounting Standards Update 2014-09 [Member]
Disaggregation Of Revenue [Line Items]
Cumulative increase to opening balance of retained earnings						$ 0.3
Impact of restatement on revenue not previously recognized						$ 5.3
Effect on revenue			3.3
Accounting Standards Update 2014-09 [Member] \| Accounts Receivable, Net
Disaggregation Of Revenue [Line Items]
Contract assets	$ 15.9		$ 15.9		$ 5.3

Revenue Recognition - Schedule of Revenue Recognized Net Impact of Adopting Topic 606 Decrease in Sales and Cost of Sales (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation Of Revenue [Line Items]
Sales	$ 436.0	$ 378.0	$ 842.1	$ 724.6
Cost of sales (excluding items below)	352.8	294.6	664.2	569.5
RUPS [Member]
Disaggregation Of Revenue [Line Items]
Sales	177.2	$ 135.9	285.6	$ 271.4
Accounting Standards Update 2014-09 [Member]
Disaggregation Of Revenue [Line Items]
Sales			3.3
Accounting Standards Update 2014-09 [Member] \| Difference between Revenue Guidance in Effect before and after Topic 606 \| RUPS [Member]
Disaggregation Of Revenue [Line Items]
Sales	(0.7)		(2.0)
Cost of sales (excluding items below)	$ (0.7)		$ (1.9)

Comprehensive (Loss) Income and Equity - Schedule of Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
Net income	$ 1.0	$ 19.8	$ 24.7	$ 24.4
Other comprehensive (loss) income:
Change in currency translation adjustment	(17.2)	4.9	(16.0)	10.9
Unrealized (loss) gain on cash flow hedges, net of tax (benefit) expense of $(2.2), $(0.3), $(6.7) and $0.6	(4.7)	(0.4)	(14.0)	0.9
Change in accounting standard	0.0	0.0	0.3	0.0
Unrecognized pension net loss, net of tax expense of $0.1, $0.2, $0.2 and $0.4	0.2	0.4	0.5	0.7
Total comprehensive (loss) income	(20.7)	24.7	(4.5)	36.9
Less: Comprehensive (loss) income attributable to noncontrolling interests	(0.3)	0.2	5.8	0.4
Comprehensive (loss) income attributable to Koppers	$ (20.4)	$ 24.5	$ (10.3)	$ 36.5

Comprehensive (Loss) Income and Equity - Schedule of Comprehensive (Loss) Income (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
Tax (benefit) expense, unrealized gains on cash flow hedges	$ (2.2)	$ (0.3)	$ (6.7)	$ 0.6
Tax expense, unrecognized pension net income	$ 0.1	$ 0.2	$ 0.2	$ 0.4

Comprehensive (Loss) Income and Equity - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
Income related to derivative instrument	$ 2.9	$ 1.3	$ 5.4	$ 2.6

Comprehensive (Loss) Income and Equity - Schedule of Change in Equity (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			$ 105.8	$ 34.6
Net income	$ 1.0	$ 19.8	24.7	24.4
Issuance of common stock			2.2	1.9
Employee stock plans			6.0	5.3
Other comprehensive (loss) income			(29.2)	12.5
Repurchases of common stock			(7.4)	(5.2)
Balance	102.1	73.5	102.1	73.5
Total Koppers Shareholders' Equity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			99.9	30.4
Net income			18.4	24.1
Issuance of common stock			2.2	1.9
Employee stock plans			6.0	5.3
Other comprehensive (loss) income			(28.7)	12.4
Repurchases of common stock			(7.4)	(5.2)
Balance	90.4	68.9	90.4	68.9
Noncontrolling Interests [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			5.9	4.2
Net income			6.3	0.3
Issuance of common stock			0.0	0.0
Employee stock plans			0.0	0.0
Other comprehensive (loss) income			(0.5)	0.1
Repurchases of common stock			0.0	0.0
Balance	$ 11.7	$ 4.6	$ 11.7	$ 4.6

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669619-108580

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669625-108580

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 55
-Paragraph 4J
-URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4591551-111686

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3000-108585

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569616-111683

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8933-108599

Reference 10: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 55
-Paragraph 4K
-URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4591552-111686

+ Details

Earnings per Common Share - Schedule of Computation of Basic and Diluted Earnings per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to Koppers	$ 0.6	$ 19.7	$ 18.4	$ 24.1
Less: Income (loss) from discontinued operations	0.5	(1.1)	0.4	(1.2)
Income from continuing operations attributable to Koppers	$ 0.1	$ 20.8	$ 18.0	$ 25.3
Weighted average common shares outstanding:
Basic	21,138	20,782	21,016	20,752
Effect of dilutive securities	916	1,101	1,076	1,146
Diluted	22,054	21,883	22,092	21,898
Income per common share – continuing operations:
Basic income per common share	$ 0.01	$ 1.00	$ 0.86	$ 1.22
Diluted income per common share	$ 0.01	$ 0.95	$ 0.81	$ 1.15
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share	249	509	195	344

Stock-based Compensation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future gross compensation expense related to non-vested stock-based compensation arrangements, which are expected to vest		$ 21.6
Future compensation expense, weighted-average expected period of recognition in months		28 months
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] \| March 2016 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period			3 years
Vesting performance stock units if minimum performance criteria are not achieved			0
Stock options, term in years			3 years
Vesting Percentage	200.00%
Performance Stock Units [Member] \| March 2016 and Thereafter Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period		3 years
Vesting performance stock units if minimum performance criteria are not achieved		0
Stock options, term in years		3 years
Performance Stock Units [Member] \| Maximum [Member] \| March 2016 Grant [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] \| Maximum [Member] \| March 2016 and Thereafter Grant [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] \| March 2016 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants			0.00%
Performance Stock Units [Member] \| Minimum [Member] \| March 2016 and Thereafter Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants		0.00%
Employee Stock Option [Member] \| 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 [Member] \| Executive Officer \| 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

Stock-based Compensation - Performance Award Fair Value Assumptions (Detail)	6 Months Ended
	Jun. 30, 2018 $ / shares
May 2018 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 39.10
Expected dividend yield per share	0.00%
Expected volatility	37.05%
Risk-free interest rate	2.82%
Grant date fair value per share	$ 15.48
May 2018 Grant [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 39.10
Expected dividend yield per share	0.00%
Expected volatility	39.40%
Risk-free interest rate	2.35%
Look-back period in years	2 years 10 months 2 days
Grant date fair value per share	$ 44.29
March 2018 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 41.60
Expected dividend yield per share	0.00%
Expected volatility	37.05%
Risk-free interest rate	2.67%
Grant date fair value per share	$ 16.38
March 2018 Grant [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 41.60
Expected dividend yield per share	0.00%
Expected volatility	39.40%
Risk-free interest rate	2.35%
Look-back period in years	2 years 10 months 2 days
Grant date fair value per share	$ 47.12
March 2017 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 44.10
Expected dividend yield per share	0.00%
Expected volatility	39.70%
Risk-free interest rate	2.13%
Grant date fair value per share	$ 17.90
March 2017 Grant [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 44.10
Expected dividend yield per share	0.00%
Expected volatility	43.50%
Risk-free interest rate	1.54%
Look-back period in years	2 years 9 months 29 days
Grant date fair value per share	$ 64.02
March 2016 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 18.11
Expected dividend yield per share	0.00%
Expected volatility	40.86%
Risk-free interest rate	1.45%
Grant date fair value per share	$ 7.41
March 2016 Grant [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 18.11
Expected dividend yield per share	0.00%
Expected volatility	40.86%
Risk-free interest rate	0.96%
Look-back period in years	2 years 10 months 2 days
Grant date fair value per share	$ 23.70

Stock-based Compensation - Summary of Performance Stock Units (Detail) - shares	Jun. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	749,329	819,691
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	499,629	581,551
Minimum [Member] \| 2016 - 2018 [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	0
Minimum [Member] \| 2017 - 2019 [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	0
Minimum [Member] \| 2018 - 2020 [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	0
Target Shares [Member] \| 2016 - 2018 [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	255,172
Target Shares [Member] \| 2017 - 2019 [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	113,675
Target Shares [Member] \| 2018 - 2020 [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	130,782
Maximum [Member] \| 2016 - 2018 [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	510,344
Maximum [Member] \| 2017 - 2019 [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	227,350
Maximum [Member] \| 2018 - 2020 [Member] \| Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	261,564

Stock-based Compensation - Summary of Status and Activity of Non-Vested Stock Units (Detail)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	819,691
Granted	245,094
Performance share adjustment	204,866
Vested	(501,821)
Forfeited	(18,501)
Non-vested, Ending Balance	749,329
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit \| $ / shares	$ 29.14
Granted, Weighted Average Grant Date Fair Value per Unit \| $ / shares	44.18
Performance share adjustment \| $ / shares	17.57
Vested, Weighted Average Grant Date Fair Value per Unit \| $ / shares	19.35
Forfeited, Weighted Average Grant Date Fair Value per Unit \| $ / shares	38.77
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit \| $ / shares	$ 37.20
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	238,140
Granted	110,743
Performance share adjustment	0
Vested	(92,089)
Forfeited	(7,094)
Non-vested, Ending Balance	249,700
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	581,551
Granted	134,351
Performance share adjustment	204,866
Vested	(409,732)
Forfeited	(11,407)
Non-vested, Ending Balance	499,629

Stock-based Compensation - Stock Options Fair Value Assumptions (Detail)	6 Months Ended
	Jun. 30, 2018 $ / shares
May 2018 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 39.10
Expected dividend yield per share	0.00%
Expected life in years	5 years 8 months 23 days
Expected volatility	37.05%
Risk-free interest rate	2.82%
Grant date fair value per share	$ 15.48
March 2018 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 41.60
Expected dividend yield per share	0.00%
Expected life in years	5 years 8 months 23 days
Expected volatility	37.05%
Risk-free interest rate	2.67%
Grant date fair value per share	$ 16.38
March 2017 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 44.10
Expected dividend yield per share	0.00%
Expected life in years	5 years 9 months 7 days
Expected volatility	39.70%
Risk-free interest rate	2.13%
Grant date fair value per share	$ 17.90
March 2016 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 18.11
Expected dividend yield per share	0.00%
Expected life in years	5 years 11 months 15 days
Expected volatility	40.86%
Risk-free interest rate	1.45%
Grant date fair value per share	$ 7.41
March 2015 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 17.57
Expected dividend yield per share	3.40%
Expected life in years	5 years 9 months
Expected volatility	42.27%
Risk-free interest rate	1.73%
Grant date fair value per share	$ 5.20

Stock-based Compensation - Summary of Status and Activity of Stock Options (Detail) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options, Outstanding at December 31, 2017 \| shares	942,537
Options, Granted \| shares	144,825
Options, Exercised \| shares	(65,897)
Options, Forfeited \| shares	(12,329)
Options, Outstanding at June 30, 2018 \| shares	1,009,136
Options, Exercisable at June 30, 2018 \| shares	621,771
Weighted Average Exercise Price per Option, Outstanding at December 31, 2017 \| $ / shares	$ 27.59
Weighted Average Exercise Price per Option, Granted \| $ / shares	41.50
Weighted Average Exercise Price per Option, Exercised \| $ / shares	28.59
Weighted Average Exercise Price per Option, Forfeited \| $ / shares	30.49
Weighted Average Exercise Price per Option, Outstanding at June 30, 2018 \| $ / shares	29.48
Weighted Average Exercise Price per Option, Exercisable at June 30, 2018 \| $ / shares	$ 28.40
Weighted Average Remaining Contractual Term, Outstanding at June 30, 2018	6 years 4 months 13 days
Weighted Average Remaining Contractual Term, Exercisable at June 30, 2018	5 years 1 month 9 days
Aggregate Intrinsic Value, Outstanding at June 30, 2018 \| $	$ 10.4
Aggregate Intrinsic Value, Exercisable at June 30, 2018 \| $	$ 6.7

Stock-based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock-based compensation expense recognized:
Less related income tax benefit	$ 1.0	$ 0.7	$ 1.9	$ 1.2
Decrease in net income attributable to Koppers	2.1	2.0	4.1	3.8
Intrinsic value of exercised stock options	0.8	0.3	1.0	1.1
Cash received from the exercise of stock options	0.9	0.3	2.2	1.9
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense recognized:
Stock-based compensation expense	$ 3.1	$ 2.7	$ 6.0	$ 5.0

Segment Information - Additional Information (Detail)	6 Months Ended
Segment Information - Additional Information (Detail)	Jun. 30, 2018 Segment
Segment Reporting [Abstract]
Number of reportable segments	3

Segment Information - Summary of Results of Segment Operations (Detail) - USD ($)
$ in Millions

3 Months Ended

6 Months Ended

Jun. 30, 2018

Jun. 30, 2017

Jun. 30, 2018

Jun. 30, 2017

$ 436.0

$ 378.0

$ 842.1

$ 724.6

13.7

11.7

25.5

22.9

Railroad and Utility Products and Services [Member]

22.3

38.1

65.6

66.2

Performance Chemicals [Member]

177.2

135.9

285.6

271.4

Carbon Materials and Chemicals [Member]

115.1

111.8

212.5

208.5

Operating Segments [Member] | Railroad and Utility Products and Services [Member]

143.7

130.3

344.0

244.7

177.2

135.9

285.6

271.4

4.9

2.9

7.9

5.9

Operating Segments [Member] | Performance Chemicals [Member]

^[1]

(1.0)

11.3

0.1

20.6

115.1

111.8

212.5

208.5

4.5

8.9

Operating Segments [Member] | Carbon Materials and Chemicals [Member]

11.6

19.6

17.2

38.2

143.7

130.3

344.0

244.7

4.3

8.7

8.1

12.5

8.0

49.7

8.6

Intersegment [Member]

Intersegment [Member] | Performance Chemicals [Member]

21.6

20.5

41.6

41.1

Intersegment [Member] | Carbon Materials and Chemicals [Member]

2.4

1.5

4.2

3.2

Corporate, Non-Segment [Member]

19.2

19.0

37.4

37.9

Segment Reporting Asset Reconciling Item [Line Items]

^[2]

$ (0.8)

$ (1.4)

$ (1.2)

[1]	Operating loss for the three and six months ended June 30, 2018 includes $5.5 million of inventory fair value purchase price adjustment related to the Company’s UIP acquisition.
[2]	Operating loss for Corporate includes primarily general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc.

Segment Information - Summary of Results of Segment Operations (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues from external customers:
Operating profit (loss)	$ 22.3	$ 38.1	$ 65.6	$ 66.2
Koppers Utility and Industrial Products [Member] \| Inventory Fair Value Purchase Price Adjustment [Member]
Revenues from external customers:
Operating profit (loss)	$ (5.5)		$ (5.5)

Segment Information - Schedule of Segment Revenues for Significant Product Lines (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net sales	$ 436.0	$ 378.0	$ 842.1	$ 724.6
Railroad and Utility Products and Services [Member]
Segment Reporting Information [Line Items]
Net sales	177.2	135.9	285.6	271.4
Railroad and Utility Products and Services [Member] \| Railroad Treated Products [Member]
Segment Reporting Information [Line Items]
Net sales	88.0	101.1	163.1	203.8
Railroad and Utility Products and Services [Member] \| Utility Poles [Member]
Segment Reporting Information [Line Items]
Net sales	58.9	10.4	70.4	21.2
Railroad and Utility Products and Services [Member] \| Rail Joints [Member]
Segment Reporting Information [Line Items]
Net sales	9.7	7.6	18.1	15.0
Railroad and Utility Products and Services [Member] \| Railroad Infrastructure Services [Member]
Segment Reporting Information [Line Items]
Net sales	9.1	9.3	16.1	17.9
Railroad and Utility Products and Services [Member] \| Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	11.5	7.5	17.9	13.5
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	115.1	111.8	212.5	208.5
Performance Chemicals [Member] \| Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	2.3	2.7	4.4	4.9
Performance Chemicals [Member] \| Wood Preservative Products [Member]
Segment Reporting Information [Line Items]
Net sales	112.8	109.1	208.1	203.6
Carbon Materials and Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	143.7	130.3	344.0	244.7
Carbon Materials and Chemicals [Member] \| Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	10.4	12.2	23.3	25.8
Carbon Materials and Chemicals [Member] \| Pitch and Related Products [Member]
Segment Reporting Information [Line Items]
Net sales	86.0	68.6	215.2	116.8
Carbon Materials and Chemicals [Member] \| Phthalic Anhydride and Other Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	18.4	21.6	40.6	44.8
Carbon Materials and Chemicals [Member] \| Creosote and Distillates [Member]
Segment Reporting Information [Line Items]
Net sales	19.3	19.0	42.2	39.5
Carbon Materials and Chemicals [Member] \| Naphthalene [Member]
Segment Reporting Information [Line Items]
Net sales	$ 9.6	$ 8.8	$ 22.7	$ 17.9

Segment Information - Summary of Tangible and Intangible Assets by Segments (Detail) - USD ($)
$ in Millions

Jun. 30, 2018

Dec. 31, 2017

Railroad and Utility Products and Services [Member] | Operating Segments [Member]

$ 1,531.7

$ 1,200.2

Goodwill

296.4

188.2

Segment Reporting Asset Reconciling Item [Line Items]

Performance Chemicals [Member] | Operating Segments [Member]

551.9

249.7

Goodwill

^[1]

120.2

10.5

Segment Reporting Asset Reconciling Item [Line Items]

Carbon Materials and Chemicals [Member] | Operating Segments [Member]

486.7

494.0

Goodwill

176.1

177.7

Segment Reporting Asset Reconciling Item [Line Items]

All Other [Member] | Operating Segments [Member]

454.8

414.2

Segment Reporting Asset Reconciling Item [Line Items]