Koppers (KOP) 10-K 27 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	KOP
Entity Registrant Name	Koppers Holdings Inc.
Entity Central Index Key	1,315,257
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		20,778,448
Entity Public Float			$ 735.2

Consolidated Statement of Opera

Consolidated Statement of Operations - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net sales	$ 1,475,500,000	$ 1,416,200,000	$ 1,626,900,000
Cost of sales (excluding items below)	1,154,100,000	1,127,900,000	1,366,700,000
Depreciation and amortization	49,800,000	52,900,000	59,000,000
Gain on sale of business	0	(2,100,000)	(3,200,000)
Impairment and restructuring charges	16,200,000	20,100,000	42,200,000
Goodwill impairment	0	0	67,200,000
Loss on pension settlements	10,000,000	4,400,000	0
Selling, general and administrative expenses	133,300,000	126,600,000	124,600,000
Operating profit (loss)	112,100,000	86,400,000	(29,600,000)
Other income, net	4,000,000	2,900,000	200,000
Interest expense	42,500,000	50,800,000	50,700,000
Loss on extinguishment of debt	13,300,000	0	0
Income (loss) before income taxes	60,300,000	38,500,000	(80,100,000)
Income tax provision (benefit)	29,000,000	11,400,000	(4,200,000)
Income (loss) from continuing operations	31,300,000	27,100,000	(75,900,000)
(Loss) income from discontinued operations, net of tax benefit (expense) of $0.2, $(0.3) and $0.1	(800,000)	600,000	(100,000)
Net income (loss)	30,500,000	27,700,000	(76,000,000)
Net income (loss) attributable to noncontrolling interests	1,400,000	(1,600,000)	(4,000,000)
Net income (loss) attributable to Koppers	$ 29,100,000	$ 29,300,000	$ (72,000,000)
Basic -
Continuing operations	$ 1.44	$ 1.39	$ (3.50)
Discontinued operations	(0.04)	0.03	(0.01)
Earnings (loss) per basic common share	1.40	1.42	(3.51)
Diluted -
Continuing operations	1.36	1.36	(3.50)
Discontinued operations	(0.04)	0.03	(0.01)
Earnings (loss) per diluted common share	$ 1.32	$ 1.39	$ (3.51)
Weighted average shares outstanding (in thousands):
Basic	20,754	20,636	20,541
Diluted	22,000	21,055	20,541

Consolidated Statement of Oper3

Consolidated Statement of Operations (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
(Loss) income from discontinued operations, tax benefit (expense)	$ 0.2	$ (0.3)	$ 0.1

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 30.5	$ 27.7	$ (76)
Changes in other comprehensive income (loss):
Currency translation adjustment	17	(4.3)	(20.6)
Derivative financial instrument net gain (loss), net of tax (expense) benefit of $(3.5), $(8.0) and $1.2	6.1	12.9	(2.2)
Unrecognized pension prior service benefit, net of tax benefit of $0.0, $0.0 and $0.4	0	0	(0.7)
Unrecognized pension net gain, net of tax expense of $(2.8), $(2.0) and $(1.0)	8.8	2.3	3.7
Total comprehensive income (loss)	62.4	38.6	(95.8)
Comprehensive income (loss) attributable to noncontrolling interests	1.7	(1.9)	(4.3)
Comprehensive income (loss) attributable to Koppers	$ 60.7	$ 40.5	$ (91.5)

Consolidated Statement of Comp5

Consolidated Statement of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Tax (expense), derivative financial instrument	$ (3.5)	$ (8)	$ 1.2
Unrecognized pension prior service benefit, tax benefit	0	0	0.4
Unrecognized pension net gain, net of tax expense	$ 2.8	$ 2	$ 1

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 60.3	$ 20.8
Accounts receivable, net of allowance of $2.5 and $3.8	159.2	136.8
Income tax receivable	1.7	3.8
Inventories, net	236.9	228.7
Loan to related party	0	8.9
Other current assets	48.6	39.1
Total current assets	506.7	438.1
Property, plant and equipment, net	328	280.8
Goodwill	188.2	186.4
Intangible assets, net	129.6	141.9
Deferred tax assets	18.4	27.1
Other assets	29.3	13.2
Total assets	1,200.2	1,087.5
Liabilities
Accounts payable	141.9	144.2
Accrued liabilities	127.9	106.3
Current maturities of long-term debt	11.4	42.6
Total current liabilities	281.2	293.1
Long-term debt	665.6	619.8
Accrued postretirement benefits	46.3	51.6
Deferred tax liabilities	7.3	6.3
Other long-term liabilities	94	82.1
Total liabilities	1,094.4	1,052.9
Commitments and contingent liabilities (Note 20)
Equity
Senior Convertible Preferred Stock, $0.01 par value per share; 10,000,000 shares authorized; no shares issued	0	0
Common Stock, $0.01 par value per share; 80,000,000 shares authorized; 22,384,476 and 22,140,680 shares issued	0.2	0.2
Additional paid-in capital	190.6	176.5
Retained earnings (accumulated deficit)	7.4	(24.7)
Accumulated other comprehensive loss	(40.1)	(68.6)
Treasury stock, at cost, 1,606,028 and 1,475,792 shares	(58.2)	(53)
Total Koppers shareholders’ equity	99.9	30.4
Noncontrolling interests	5.9	4.2
Total equity	105.8	34.6
Total liabilities and equity	$ 1,200.2	$ 1,087.5

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Accounts receivable, allowance	$ 2.5	$ 3.8
Senior Convertible Preferred Stock, par value	$ 0.01	$ 0.01
Senior Convertible Preferred Stock, shares authorized	10,000,000	10,000,000
Senior Convertible Preferred Stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	80,000,000	80,000,000
Common Stock, shares issued	22,384,476	22,140,680
Treasury stock, shares	1,606,028	1,475,792

Consolidated Statement of Cash

Consolidated Statement of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash provided by (used in) operating activities:
Net income (loss)	$ 30,500,000	$ 27,700,000	$ (76,000,000)
Adjustments to reconcile net cash provided by operating activities:
Depreciation and amortization	49,800,000	52,900,000	59,000,000
Impairment of long-lived assets	3,700,000	3,500,000	14,700,000
Goodwill impairment	0	0	67,200,000
Loss on extinguishment of debt	13,300,000	0	0
Gain on disposal of assets and investment	(1,500,000)	0	0
Gain on sale of business	0	(2,100,000)	(3,200,000)
Deferred income taxes	1,600,000	(100,000)	(16,000,000)
Equity loss, net of dividends received	0	1,000,000	3,100,000
Change in other liabilities	(21,100,000)	(5,000,000)	(5,500,000)
Non-cash interest expense	2,100,000	5,700,000	3,600,000
Stock-based compensation	10,600,000	8,900,000	3,800,000
Deferred revenue	(700,000)	(800,000)	27,600,000
Loss on pension settlement	10,000,000	4,400,000	0
Other - net	(100,000)	1,700,000	5,200,000
Changes in working capital:
Accounts receivable	(16,000,000)	12,700,000	34,100,000
Inventories	700,000	(3,300,000)	(4,300,000)
Accounts payable	(13,600,000)	5,000,000	25,000,000
Accrued liabilities	31,200,000	8,400,000	(19,600,000)
Other working capital	1,300,000	(1,100,000)	9,000,000
Net cash provided by operating activities	101,800,000	119,500,000	127,700,000
Cash provided by (used in) investing activities:
Capital expenditures	(67,500,000)	(49,900,000)	(40,700,000)
Repayments received on loan	9,500,000	0	0
Acquisitions, net of cash acquired	0	0	(15,300,000)
Net cash provided by (used in) divestitures and asset sales	1,500,000	(3,800,000)	14,900,000
Net cash used in investing activities	(56,500,000)	(53,700,000)	(41,100,000)
Cash provided by (used in) financing activities:
Borrowings of revolving credit	705,400,000	595,700,000	612,100,000
Repayments of revolving credit	(651,100,000)	(625,400,000)	(685,900,000)
Borrowings of long-term debt	500,000,000	0	1,100,000
Repayments of long-term debt	(546,700,000)	(31,700,000)	(40,700,000)
Issuances of Common Stock	2,700,000	400,000	0
Repurchases of Common Stock	(5,200,000)	(300,000)	(300,000)
Payment of debt issuance costs	(11,000,000)	(1,400,000)	(1,000,000)
Dividends paid	0	0	(8,700,000)
Net cash (used in) provided by financing activities	(5,900,000)	(62,700,000)	(123,400,000)
Effect of exchange rate changes on cash	100,000	(4,100,000)	7,500,000
Net increase (decrease) in cash and cash equivalents	39,500,000	(1,000,000)	(29,300,000)
Cash and cash equivalents at beginning of period	20,800,000	21,800,000	51,100,000
Cash and cash equivalents at end of period	60,300,000	20,800,000	21,800,000
Cash paid during the year for:
Interest	37,600,000	42,700,000	43,900,000
Income taxes, net	16,600,000	11,600,000	26,300,000
Noncash investing activities:
Accrued capital expenditures	$ 7,800,000	$ 0	$ 0

Consolidated Statement of Share

Consolidated Statement of Shareholders' Equity - USD ($) $ in Millions	Total	Senior Convertible Preferred Stock [Member]	Common Stock [Member]	Noncontrolling Interests [Member]	Retained Earnings (Accumulated Deficit) [Member]	Currency Translation Adjustment [Member]	Unrecognized Gains (Losses) on Cash Flow Hedges [Member]	Unrecognized Pension Prior Service Cost [Member]	Unrecognized Pension Net Loss [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Koppers Shareholder's Equity (Deficit) [Member]
Balance at Dec. 31, 2014		$ 0	$ 0.2	$ 13.9	$ 18	$ (6.3)	$ (3.8)	$ 0.7	$ (50.9)	$ 164.5	$ (52.4)
Net income (loss) attributable to noncontrolling interests	$ (4)			(4)
Net income (loss) attributable to Koppers	(72)				(72)
Tax reform rate change reclassification					0		0		0
Change in accounting standard					0
Purchases											(0.3)
Change in currency translation adjustment	(20.6)			(0.3)		(20.3)
Reclassification of unrealized (gains) losses on cash flow hedges to expense, net of tax (expense) benefit of $(5.0), $3.7 and $3.5	5.4
Change in cash flow hedges, net of tax (expense) benefit of $(8.5), $(4.3) and $4.7							(7.6)
Reclassification of unrecognized prior service benefit to income,net of tax benefit of $0.0, $0.0 and $0.4								(0.7)
Reclassification of unrecognized pension net loss to expense, net of tax benefit of $4.4, $2.3 and $2.2									4
Revaluation of unrecognized pension net loss, net of taxbenefit of $0.2, $0.3 and $1.2									(0.3)
Dividends to noncontrolling interests				(3.5)
Employee stock plans										3.3
Issuance of common stock										0
Balance at Dec. 31, 2015	(12.4)	0	0.2	6.1	(54)	(26.6)	(6)	0	(47.2)	167.8	(52.7)	$ (79.8)	$ (18.5)
Net income (loss) attributable to noncontrolling interests	(1.6)			(1.6)
Net income (loss) attributable to Koppers	29.3				29.3
Tax reform rate change reclassification					0		0		0
Change in accounting standard					0
Purchases											(0.3)
Change in currency translation adjustment	(4.3)			(0.3)		(4)
Reclassification of unrealized (gains) losses on cash flow hedges to expense, net of tax (expense) benefit of $(5.0), $3.7 and $3.5	5.6
Change in cash flow hedges, net of tax (expense) benefit of $(8.5), $(4.3) and $4.7							7.3
Reclassification of unrecognized prior service benefit to income,net of tax benefit of $0.0, $0.0 and $0.4								0
Reclassification of unrecognized pension net loss to expense, net of tax benefit of $4.4, $2.3 and $2.2									3.9
Revaluation of unrecognized pension net loss, net of taxbenefit of $0.2, $0.3 and $1.2									(1.6)
Dividends to noncontrolling interests				0
Employee stock plans										8.7
Issuance of common stock										0
Balance at Dec. 31, 2016	34.6	$ 0	$ 0.2	4.2	(24.7)	(30.6)	6.9	0	(44.9)	176.5	(53)	(68.6)	30.4
Net income (loss) attributable to noncontrolling interests	1.4			1.4
Net income (loss) attributable to Koppers	29.1				29.1
Tax reform rate change reclassification					3.2		2.8		(6)
Change in accounting standard					(0.2)
Purchases											(5.2)
Change in currency translation adjustment	17			0.3		16.8
Reclassification of unrealized (gains) losses on cash flow hedges to expense, net of tax (expense) benefit of $(5.0), $3.7 and $3.5	(7.1)
Change in cash flow hedges, net of tax (expense) benefit of $(8.5), $(4.3) and $4.7							13.2
Reclassification of unrecognized prior service benefit to income,net of tax benefit of $0.0, $0.0 and $0.4								0
Reclassification of unrecognized pension net loss to expense, net of tax benefit of $4.4, $2.3 and $2.2									7.3
Revaluation of unrecognized pension net loss, net of taxbenefit of $0.2, $0.3 and $1.2									1.5
Dividends to noncontrolling interests				0
Employee stock plans										11.4
Issuance of common stock										2.7
Balance at Dec. 31, 2017	$ 105.8			$ 5.9	$ 7.4	$ (13.8)	$ 15.8	$ 0	$ (42.1)	$ 190.6	$ (58.2)	$ (40.1)	$ 99.9

Consolidated Statement of Sha10

Consolidated Statement of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrecognized Gains (Losses) on Cash Flow Hedges [Member]
Unrealized (gains) losses on cash flow hedges to expense, tax (benefit) expense	$ (5)	$ 3.7	$ 3.5
Deferred losses on cash flow hedges, tax (expense) benefit	(8.5)	(4.3)	4.7
Unrecognized Pension Prior Service Cost [Member]
Reclassification of unrecognized pension prior service benefit, tax benefit	0	0	0.4
Unrecognized Pension Net Loss [Member]
Reclassification of unrecognized pension net loss, tax expense	4.4	2.3	2.2
Revaluation of unrecognized pension net loss, tax benefit	$ 0.2	$ 0.3	$ 1.2

Description of Business

Description of Business	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Description of Business	1. Description of Business Parent company of Koppers Inc. – In these financial statements, unless otherwise indicated or the context requires otherwise, when the terms “Koppers,” the “Company,” “we,” “our” or “us,” are used, they mean Koppers Holdings Inc. (“Koppers Holdings”) and its subsidiaries on a consolidated basis. The use of these terms is not intended to imply that Koppers Holdings and Koppers Inc. are not separate and distinct legal entities from each other and from their respective subsidiaries. Koppers Holdings has no direct operations and no significant assets other than the stock of Koppers Inc. It depends on the dividends from the earnings of Koppers Inc. and its subsidiaries to generate the funds necessary to meet its financial obligations. The terms of Koppers Inc.’s Revolving Credit Facility prohibit Koppers Inc. from paying dividends and otherwise transferring assets except for certain limited dividends. Further, the terms of the indenture governing Koppers Inc.’s Senior Notes due 2025 significantly restrict Koppers Inc. from paying dividends and otherwise transferring assets to Koppers Holdings. Business description – The Company is a global integrated provider of treated wood products, wood treatment chemicals and carbon compounds for use in a variety of markets including the railroad, specialty chemical, utility, residential lumber, agriculture, aluminum, steel, rubber and construction industries. The Company’s business is operated through three business segments, Railroad and Utility Products and Services (“RUPS”), Performance Chemicals (“PC”) and Carbon Materials and Chemicals (“CMC”). The Company’s Railroad and Utility Products and Services segment sells treated and untreated wood products, rail joint bars and services primarily to the railroad industry and treated wood products to the utility industry. Railroad products include procuring and treating items such as crossties, switch ties and various types of lumber used for railroad bridges and crossings and the manufacture of rail joint bars. Utility products include transmission and distribution poles and pilings. The Company’s Performance Chemicals segment develops, manufactures, and markets wood preservation chemicals and wood treatment technologies and services a diverse range of end-markets including infrastructure, residential and commercial construction and agriculture. The Company’s Carbon Materials and Chemicals segment is primarily a manufacturer of creosote, carbon pitch, naphthalene, phthalic anhydride and carbon black feedstock. Creosote is used in the treatment of wood and carbon black feedstock is used in the production of carbon black. Carbon pitch is a critical raw material used in the production of aluminum and for the production of steel in electric arc furnaces. Naphthalene is used for the production of phthalic anhydride and as a surfactant in the production of concrete. Phthalic anhydride is used in the production of plasticizers, polyester resins and alkyd paints.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of presentation – The consolidated financial statements include the accounts of the Company and all majority-owned subsidiaries for which the Company is deemed to exercise control over its operations. All significant intercompany transactions have been eliminated in consolidation. The Company’s investments in 20 percent to 50 percent-owned companies in which it has the ability to exercise significant influence over operating and financial policies are accounted for using the equity method of accounting. Accordingly, the Company’s share of the earnings of these companies is included in the accompanying consolidated statement of operations. As of November 2016, the Company had no investments under the equity method of accounting. Certain prior period amounts in the notes to the consolidated financial statements have been reclassified to conform to the current period’s presentation. Use of estimates – Accounting principles generally accepted in the U.S. require management to make estimates and judgments that affect the reported amounts of assets and liabilities and the disclosure of contingencies on the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Estimates have been prepared on the basis of the most current and best available information and actual results could differ materially from these estimates. Foreign currency translation – For consolidated entities outside of the U.S. that prepare financial statements in currencies other than the U.S. dollar, results of operations and cash flows are translated at average exchange rates during the period, and assets and liabilities are translated at end-of-period exchange rates. Cumulative translation adjustments are included as a separate component of accumulated other comprehensive loss in shareholders’ equity. Foreign currency transaction gains and losses result from transactions denominated in a currency which is different than the currency used by the entity to prepare its financial statements. Foreign currency transaction losses were $2.3 million, $1.3 million and $10.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. Revenue recognition – The Company recognizes revenue when the risks and rewards of ownership and title to the product have transferred to the customer. Revenue recognition generally occurs at the point of shipment; however in certain circumstances as shipping terms dictate, revenue is recognized at the point of destination. Shipping and handling costs are included as a component of cost of sales. The Company recognizes revenue related to the procurement of certain untreated railroad crossties upon transfer of title to the customer, which occurs upon delivery to the Company’s plant and acceptance by the customer. Payment on sales of untreated railroad crossties and wood treating services are generally due within 30 days of the invoice date. Service revenue, consisting primarily of wood treating services, is recognized at the time the service is provided. The Company’s recognition of revenue with respect to untreated crossties meets all the recognition criteria of Securities and Exchange Commission Staff Accounting Bulletin Topic 13.A.3., including transfer of title and risk of ownership, the existence of fixed purchase commitments and delivery schedules established by the customer, and the completion of all performance obligations by the Company. Revenue recognized for untreated crosstie sales for the years ended December 31, 2017, 2016 and 2015 amounted to $96.8 million, $129.2 million and $129.8 million, respectively. Research and development – Research and development costs are expensed as incurred and are included in selling, general and administrative expenses. These costs totaled $9.0 million in 2017, $6.6 million in 2016 and $5.2 million in 2015. Cash and cash equivalents – Cash and cash equivalents include cash on hand and on deposit and investments in highly liquid investments with an original maturity of 90 days or less. Accounts receivable – The Company maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments. In circumstances where the Company becomes aware of a specific customer’s inability to meet its financial obligations to Koppers, a specific reserve for bad debts is recorded against amounts due. If the financial condition of the Company’s customers were to deteriorate, resulting in an inability to make payments, additional allowances may be required. Inventories – In the United States, CMC and RUPS inventories are valued at the lower of cost, utilizing the last-in, first-out (“LIFO”) basis, or market. PC inventories and all other inventories outside of the United States are valued at the lower of cost, utilizing the first-in, first-out (“FIFO”) basis, and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. LIFO inventories constituted approximately 52 percent and 65 percent of the FIFO inventory value at December 31, 2017 and 2016, respectively. In 2017, 2016 and 2015, we recorded inventory write-downs of $0.4 million, $0.6 million and $1.4 million, respectively, related to lower of cost and net realizable value for our subsidiaries that value inventory on the FIFO basis. Property, plant and equipment – Property, plant and equipment are recorded at purchased cost and include improvements which significantly increase capacities or extend useful lives of existing plant and equipment. Depreciation expense is calculated by applying the straight-line method over estimated useful lives. Estimated useful lives for buildings generally range from 10 to 20 years and depreciable lives for machinery and equipment generally range from 3 to 15 years. Net gains and losses related to asset disposals are recognized in earnings in the period in which the disposal occurs. Routine repairs, replacements and maintenance are expensed as incurred. The Company periodically evaluates whether current facts and circumstances indicate that the carrying value of its depreciable long-lived assets may not be recoverable. If an asset, or logical grouping of assets, is determined to be impaired, the asset is written down to its fair value using discounted future cash flows and, if available, quoted market prices. Refer to Note 4 “Plant Closures and Discontinued Operations” for additional information. Goodwill and other intangible assets – Goodwill and other purchased intangible assets are included in the identifiable assets of the business segment to which they have been assigned. The Company performs impairment tests annually for goodwill, and more often as circumstances require. When it is determined that impairment has occurred, an appropriate charge to earnings is recorded. The Company performed its annual impairment test in the fourth quarters of 2017 and 2016, noting no impairment. Refer to Note 14 "Goodwill and Other Identifiable Intangible Assets" for a discussion of goodwill impairment recorded during the year ended December 31, 2015. Identifiable intangible assets, other than goodwill, are recorded at cost. Identifiable intangible assets that do not have indefinite lives are amortized on a straight-line basis over their estimated useful lives. Deferred income taxes – Deferred tax assets and liabilities are recognized for future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. The effect on deferred tax assets and liabilities of a change in tax laws is recognized in earnings in the period the new laws are enacted. A valuation allowance is recorded to reduce the carrying amounts of deferred tax assets unless it is more likely than not that such assets will be realized. Self-insured liabilities – The Company is self-insured for property, casualty and workers’ compensation exposures up to various stop-loss coverage amounts. Losses are accrued based upon the Company’s estimates of the liability for the related deductibles of claims incurred. Such estimates utilize actuarial methods based on various assumptions, which include but are not limited to, the Company’s historical loss experience and projected loss development factors. In 2017 and 2016, reversals of self-insured liabilities occurred as a result of favorable loss trends related to self-insured claims. 2017 2016 (Dollars in millions) Self-insured liabilities at beginning of year $ 10.9 $ 8.0 Expense 1.9 5.1 Change in reserves recoverable from insurance (0.3 ) 2.4 Reversal of self-insured liabilities (0.4 ) (1.7 ) Cash expenditures (2.6 ) (2.9 ) Self-insured liabilities at end of year $ 9.5 $ 10.9 Derivative financial instruments – The Company uses swap contracts to manage copper price risk associated with forecasted purchases of materials used in the Company’s manufacturing processes. The Company uses forward contracts to hedge exposure to currency exchange rate changes on transactions and other commitments denominated in a foreign currency. Contracts are not held for trading or speculative purposes. The Company recognizes the fair value of the swap and forward contracts as an asset or liability at each reporting date. The Company designates certain of the swap and forward contracts as cash flow hedges and the effective portion of the gain or loss on the derivative is reported as a component of accumulated other comprehensive income (loss) until it is reclassified into earnings when the hedged transaction affects earnings. Gains and losses from hedge ineffectiveness are recognized in current earnings. For swap and forward contracts that are not designated as cash flow hedges, changes in the fair value of those contracts are recognized immediately in earnings. Asset retirement obligations – Asset retirement obligations are initially recorded at present value and are capitalized as part of the cost of the related long-lived asset when sufficient information is available to estimate present value. The capitalized costs are subsequently charged to depreciation expense over the estimated useful life of the related long-lived asset. The present value of the obligation is determined by calculating the discounted value of expected future cash flows and accretion expense is recorded each month to ultimately increase this obligation to full value. 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 describes changes to the Company’s asset retirement obligation liabilities at December 31, 2017 and 2016: 2017 2016 (Dollars in millions) Asset retirement obligation at beginning of year $ 36.0 $ 46.5 Divestiture 0.0 (8.0 ) Accretion expense 2.4 7.1 Revision in estimated cash flows (a) 9.4 2.7 Cash expenditures (10.9 ) (11.4 ) Currency translation 0.2 (0.9 ) Balance at end of period $ 37.1 $ 36.0 (a) Revision in estimated cash flows for 2017 and 2016 includes $9.4 and $2.7 million of charges related to restructuring activities, respectively. See Note 4. “Plant Closures and Discontinued Operations” for additional information. Litigation and contingencies – Amounts associated with litigation and contingencies are accrued when management, after taking into consideration the facts and circumstances of each matter including any settlement offers, has determined that it is probable that a liability has been incurred and the amount of loss can be reasonably estimated. Legal costs for litigation are expensed as incurred with the exception of legal fees relating to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites. Other current assets – Included in other current assets are prepaid expenses totaling $18.6 million and $17.0 million at December 31, 2017 and 2016, respectively. Environmental liabilities – The Company accrues for remediation costs and penalties when the responsibility to remediate is probable and the amount of related cost is reasonably estimable. If only a range of potential liability can be estimated and no amount within the range is more probable than another, the accrual is recorded at the low end of that range. Remediation liabilities are discounted if the amount and timing of the cash disbursements are readily determinable. Deferred revenue – The Company received an advance payment of $30.0 million in 2015 related to an amendment to a 50-year supply agreement with a customer in China. The deferred revenue associated with this amendment will be amortized over the life of the underlying contract. In addition, 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 describes changes to the Company’s deferred revenue at December 31, 2017 and 2016: 2017 2016 (Dollars in millions) Deferred revenue at beginning of year $ 27.2 $ 30.1 Revenue earned (0.7 ) (0.8 ) Currency translation 1.6 (2.1 ) Deferred revenue at end of year $ 28.1 $ 27.2 Stock-based compensation – The Company records compensation expense for non-vested stock options and stock units over the vesting period based on the fair value at the date of grant. No compensation cost is recognized for any stock awards that are forfeited in the event the recipient fails to meet the vesting requirements.

New Accounting Pronouncements

New Accounting Pronouncements	12 Months Ended
	Dec. 31, 2017
Accounting Changes And Error Corrections [Abstract]
New Accounting Pronouncements	3. New Accounting Pronouncements The Company adopted Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) No. 2016-09, “Improvements to Employee Share-Based Payment Accounting” effective January 1, 2017. This ASU makes several modifications related to the accounting for forfeitures of share-based awards, employer tax withholding on share-based compensation and the financial statement presentation of excess tax benefits or deficiencies. The Company elected to account for forfeitures when they occur. The impact of adoption was a decrease to retained earnings of $0.2 million, an increase to deferred tax assets of $0.1 million and an increase to additional paid in capital of $0.3 million. The Company adopted ASU No. 2018-02, “Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” effective October 1, 2017. ASU 2018-02 requires a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the newly enacted federal corporate income tax rate. The amount of the reclassification is the difference between the tax-effected items that are included in accumulated other comprehensive income and were recorded at the historical 35 percent corporate income tax rate and those same items that are now recorded at the newly enacted 21 percent corporate income tax rate. This difference was $3.2 million for the year ended December 31, 2017. In May 2014, the 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 are effective for annual reporting periods beginning after December 15, 2017. The Company has decided to use the modified retrospective method for transition in which the cumulative effect will be recognized at the date of adoption with no restatement of comparative periods presented. The Company has completed its analysis of significant contracts with customers across all major business units to assess the impact of the adoption of the ASUs on the Company’s financial statements and disclosures. The Company utilized a bottom-up approach to analyze the impact of the standard on its contract portfolio by reviewing its current accounting policies and practices to identify potential differences that would result from applying the requirements of the new standard to its revenue contracts. In addition, the Company identified and implemented appropriate changes to our business processes, systems and controls to support recognition and disclosure under the new standard. The implementation team has reported the findings and progress of the project to management and the Audit Committee on a frequent basis over the last year. Substantially all of the Company’s contracts with its customers are ship and invoice arrangements where revenue is recognized at the time of shipment or delivery. The Company has identified certain arrangements where revenue will be accelerated upon adoption as the related performance obligations under the contract have been satisfied and control of the goods or services have been transferred to the customer prior to shipment. After assessing the results of the completed analysis, the Company calculated the cumulative effect to the opening balance of retained earnings recognized at January 1, 2018 will be an increase of approximately $1 million, including approximately $5 million in revenue not recognized as of December 31, 2017. The impact of adopting Topic 606 is primarily related to certain services to untreated cross-ties within our RUPS segment where those specific performance obligations were fulfilled prior to shipment and historically not recognized as revenue until shipped. In August 2017, the FASB issu ed 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. ASU No. 2017-12 is effective for periods beginning after December 15, 2019, and earlier adoption is permitted. The Company will adopt this ASU effective January 1, 2018 and the impact of adoption is not expected to have a material impact on its consolidated financial statements. 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. The Company will adopt this ASU effective January 1, 2018 and does not anticipate ASU 2017-04 will impact our financial statements as there is a sufficient excess between the fair value and carrying value of our goodwill. In August 2016, the FASB 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 early adoption is permitted. The guidance requires a modified retrospective adoption. The Company is currently evaluating the impact the adoption of ASU 2016-02 will have on its consolidated financial statements.

Plant Closures and Discontinued

Plant Closures and Discontinued Operations	12 Months Ended
	Dec. 31, 2017
Discontinued Operations And Disposal Groups [Abstract]
Plant Closures and Discontinued Operations	4. Plant Closures and Discontinued Operations Over the past four years, the Company has been restructuring its Carbon Materials and Chemicals (“CMC”) business unit in order to concentrate its facilities in regions where the Company believes it holds key competitive advantages to better serve its global customers. These closure activities include: • It is anticipated that the Company will cease naphthalene refining activities its Follansbee, West Virginia coal tar distillation facility in 2018 upon commissioning of a new naphthalene refining plant in Stickney, Illinois. • In November 2016, the Company sold its 30-percent interest in Tangshan Kailuan Koppers Carbon Chemical Company Limited (“TKK”) located in the Hebei Province in China. • In July 2016, the Company discontinued coal tar distillation activities at its CMC plant located in Clairton, Pennsylvania. • In March 2016, the Company discontinued production at its 60-percent owned CMC plant located in Tangshan, China. • In February 2016, the Company ceased coal tar distillation and specialty pitch operations at both of its United Kingdom CMC facilities. In July 2016, the Company sold substantially all of its CMC tar distillation properties and assets in the United Kingdom. In exchange, the Company transferred cash to the buyer and the buyer assumed historical environmental and asset retirement obligations. • In April 2014, the Company ceased its coal tar distillation activities at its CMC facility located in Uithoorn, the Netherlands. Other closure and divestiture activity relates to the Company’s Railroad Utility Products and Services (“RUPS”) business unit. These actions include: • In October 2016, the Company agreed to a long-term lease of its wood treatment facility in Houston, Texas to a third party. • In August 2015, the Company closed its RUPS plant located in Green Spring, West Virginia. • In July 2015, the Company sold the assets of its 50-percent interest in KSA Limited Partnership, a concrete crosstie manufacturer. • In January 2015, Koppers Inc. sold its RUPS North American utility pole business. In addition, in 2011, the Company ceased carbon black production at its CMC facility located in Kurnell, Australia. Costs associated with this closure are included in “(Loss) income from discontinued operations” on the Condensed Consolidated Statement of Operations and Comprehensive Income. Details of the restructuring activities and related reserves are as follows: Severance employee Environmental remediation Asset retirement Other Total (Dollars in millions) Reserve at December 31, 2015 $ 2.0 $ 4.3 $ 21.9 $ 0.0 $ 28.2 Accrual 2.4 0.1 5.6 5.6 13.7 Costs charged against assets 0.0 0.0 0.0 (1.9 ) (1.9 ) Reversal of accrued charges (1.9 ) (0.5 ) (8.7 ) (0.1 ) (11.2 ) Cash paid (1.0 ) (2.4 ) (8.1 ) (0.2 ) (11.7 ) Currency translation (0.1 ) 0.0 (0.7 ) (0.2 ) (1.0 ) 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 Costs 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

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	5. Related Party Transactions During 2016, the Company sold its 30 percent interest in TKK. Refer to Note 16 “Debt” for detail on two committed loan facility agreements entered into by our 75-percent owned subsidiary, Koppers (Jiangsu) Carbon Chemical Company Limited (“KJCC”).

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	6. Fair Value Measurements Carrying amounts and the related estimated fair values of the Company’s financial instruments as of December 31, 2017 and 2016 are as follows: December 31, 2017 December 31, 2016 Fair Value Carrying Value Fair Value Carrying Value (Dollars in millions) Financial assets: Cash and cash equivalents, including restricted cash $ 60.3 $ 60.3 $ 20.8 $ 20.8 Investments and other assets (a) 1.1 1.1 1.1 1.1 Financial liabilities: Long-term debt (including current portion) $ 706.9 $ 688.7 $ 669.6 $ 671.1 (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 issuances 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.

Earnings per Common Share

Earnings per Common Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings per Common Share	7. Earnings per Common Share The computation of basic earnings per common share for the periods presented is based upon the weighted average number of common shares outstanding during the periods. The computation of diluted earnings per common share includes the effect of non-vested nonqualified stock options and restricted stock units assuming such options and stock units were outstanding common shares at the beginning of the period. The effect of antidilutive securities is excluded from the computation of diluted loss per common share, if any. The following table sets forth the computation of basic and diluted earnings (loss) per common share: Year Ended December 31, 2017 2016 2015 (Dollars in millions, except share amounts, in thousands, and per share amounts) Net income (loss) attributable to Koppers $ 29.1 $ 29.3 $ (72.0 ) (Loss) income from discontinued operations (0.8 ) 0.6 (0.1 ) Income (loss) from continuing operations attributable to Koppers $ 29.9 $ 28.7 $ (71.9 ) Weighted average common shares outstanding: Basic 20,754 20,636 20,541 Effect of dilutive securities 1,246 419 0 Diluted 22,000 21,055 20,541 Earnings (loss) per common share – continuing operations: Basic earnings (loss) per common share $ 1.44 $ 1.39 $ (3.50 ) Diluted earnings (loss) per common share 1.36 1.36 (3.50 ) Other data: Antidilutive securities excluded from computation of diluted earnings per common share 156 415 668

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	8. Stock-based Compensation The amended and restated 2005 Long-Term Incentive Plan (the “LTIP”) provides for the grant to eligible persons of stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance awards, dividend equivalents and other stock-based awards, which are collectively referred to as the awards. Restricted Stock Units and Performance Stock Units Under the LTIP, the board of directors grants restricted stock units and performance stock units to certain employee participants (collectively, the “stock units”). For grants to most employees in 2015 and thereafter, the restricted stock units vest in four equal annual installments. Restricted stock units that have one-year vesting periods are also issued under the LTIP to members of the board of directors in connection with annual director compensation and, from time to time, are issued to employees in connection with employee compensation with typical vesting periods of two years or less. Compensation expense for non-vested stock units is recorded over the vesting period based on the fair value at the date of grant. The fair value of restricted stock units and performance stock units with a performance condition is the market price of the underlying common stock on the date of grant. Performance stock units granted in 2015 have vesting based upon a performance condition. These performance stock units have three-year performance objectives and all performance stock units have a three-year period for vesting (if the applicable performance objective is achieved). The applicable performance objective is based upon a multi-year cumulative value creation calculation that considers the Company’s financial performance commencing on the first day of each grant year. The number of performance stock units granted represents the target award and participants have the ability to earn between zero and 200 percent (depending on the grant date) of the target award based upon actual performance. If minimum performance criteria are not achieved, no performance stock units will vest. Performance stock units granted in 2014 did not meet the value creation threshold and were forfeited in February 2017. Performance stock units granted in 2015 will vest at 200 percent in March 2018. Performance stock units granted in 2016 and 2017 have vesting based upon a market condition. These performance stock units have a three-year performance objective and a three-year period for vesting (if the applicable performance objective is achieved). The applicable performance objective is based on the Company’s total shareholder return relative to the Standard & Poors SmallCap 600 Materials Index. The number of performance stock units granted represents the target award and participants have the ability to earn between zero and 200 percent of the target award based upon actual performance. If minimum performance criteria are not achieved, no performance stock units will vest. The Company has the discretion to settle the award in cash rather than shares, although the Company currently expects that all awards will be settled by the issuance of shares. Compensation expense for non-vested performance stock units with a market condition is recorded over the vesting period based on the fair value at the date of grant. 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: March March Grant date price per share of performance award $ 44.10 $ 18.11 Expected dividend yield per share 0.00 % 0.00 % Expected volatility 43.50 % 40.86 % Risk-free interest rate 1.54 % 0.96 % Look-back period in years 2.83 2.84 Grant date fair value per share of performance award $ 64.02 $ 23.70 Dividends declared, if any, on the Company’s common stock during the period prior to vesting of the stock units are credited at equivalent value as additional stock units and become payable as additional common shares upon vesting. In the event of termination of employment, other than retirement, death or disability, any non-vested stock units are forfeited, including additional stock units credited from dividends. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the stock units over the service period will result. There are special vesting provisions for the stock units related to a change in control. The following table shows a summary of the performance stock units as of December 31, 2017: Performance Period Minimum Shares Target Shares Maximum Shares 2015 – 2017 0 203,953 407,906 2016 – 2018 0 260,588 521,176 2017 – 2019 0 117,010 234,020 The following table shows a summary of the status and activity of non-vested stock awards for the year ended December 31, 2017: Restricted Stock Units Performance Stock Units Total Stock Units Weighted Grant Date Fair Value per Unit Non-vested at January 1, 2017 279,807 554,388 834,195 $ 23.09 Granted 86,779 117,010 203,789 $ 55.14 Vested (128,276 ) 0 (128,276 ) $ 24.99 Forfeited (170 ) (89,847 ) (90,017 ) $ 37.80 Non-vested at December 31, 2017 238,140 581,551 819,691 $ 29.14 Stock Options Prior to 2015, stock options to most executive officers vest and become exercisable upon the completion of a three-year service period commencing on the grant date. For grants in 2015 and thereafter, the stock options vest in four equal annual installments. The stock options have a term of ten years. In the event of termination of employment, other than retirement, death or disability, any non-vested options are forfeited. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the options over the service period will result. There are special vesting provisions for the stock options related to a change in control. Compensation expense for non-vested stock options is recorded over the vesting period based on the fair value at the date of grant. 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: March March March 2015 Grant Grant date price per share of stock option award $ 44.10 $ 18.11 $ 17.57 Expected dividend yield per share 0.00 % 0.00 % 3.40 % Expected life in years 5.77 5.96 5.75 Expected volatility 39.70 % 40.86 % 42.27 % Risk-free interest rate 2.13 % 1.45 % 1.73 % Grant date fair value per share of option awards $ 17.90 $ 7.41 $ 5.20 The dividend yield is based on the Company’s current and prospective dividend rate which calculates a continuous dividend yield based upon the market price of the underlying common stock. The Company suspended its dividend in February 2015 and it has not been determined when and if, the dividend will be reinstated. The expected life in years is based on historical exercise data of options previously granted by the Company. Expected volatility is based on the historical volatility of the Company’s common stock and the historical volatility of certain other similar public companies. The risk-free interest rate is based on U.S. Treasury bill rates for the expected life of the option. The following table shows a summary of the status and activity of stock options for the year ended December 31, 2017: Options Weighted Exercise Price per Option Weighted Average Remaining Contractual Term (in years) Aggregate Value (in millions) Outstanding at December 31, 2016 935,454 $ 26.10 Granted 97,403 $ 44.10 Exercised (90,320 ) $ 29.95 Outstanding at December 31, 2017 942,537 $ 27.59 6.21 $ 22.0 Exercisable at December 31, 2017 530,762 $ 30.33 4.80 $ 10.9 Stock Compensation Expense Total stock-based compensation expense recognized and cash received from the exercise of stock options for the three years ended December 31, 2017, 2016 and 2015 are as follows: Year Ended December 31, 2017 2016 2015 (Dollars in millions) Stock-based compensation expense recognized: Selling, general and administrative expenses $ 10.6 $ 8.9 $ 3.8 Less related income tax benefit 4.1 3.6 1.5 Decrease in net income attributable to Koppers $ 6.5 $ 5.3 $ 2.3 Intrinsic value of exercised stock options $ 1.3 $ 0.1 $ 0.0 Cash received from the exercise of stock options $ 2.7 $ 0.4 $ 0.0 As of December 31, 2017 total future compensation expense related to non-vested stock-based compensation arrangements totaled $15.0 million and the weighted-average period over which this expense is expected to be recognized is approximately 25 months.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Information	9. Segment Information The Company has three reportable segments: Railroad and Utility Products and Services, Performance Chemicals and Carbon Materials and Chemicals. The Company’s reportable segments contain multiple aggregated business units since management believes the long-term financial performance of these business units is affected by similar economic conditions. The reportable segments are each managed separately because they manufacture and distribute distinct products with different production processes. The Company’s Railroad and Utility Products and Services segment sells treated and untreated wood products, manufactured products and services primarily to the railroad and public utility markets. Railroad products and services include procuring and treating items such as crossties, switch ties and various types of lumber used for railroad bridges and crossings and the manufacture of rail joint bars. The segment also operates a railroad services business that conducts engineering, design, repair and inspection services for railroad bridges. Utility products include the treating of transmission and distribution poles and pilings. The Company’s Performance Chemicals segment develops, manufactures, and markets wood preservation chemicals and wood treatment technologies and services a diverse range of end-markets including infrastructure, residential and commercial construction, and agriculture. The Company’s Carbon Materials and Chemicals segment is primarily a manufacturer of creosote, carbon pitch, naphthalene, phthalic anhydride and carbon black feedstock. Creosote is used in the treatment of wood and carbon black feedstock is used in the production of carbon black. Carbon pitch is a critical raw material used in the production of aluminum and for the production of steel in electric arc furnaces. Naphthalene is used for the production of phthalic anhydride and as a surfactant in the production of concrete. Phthalic anhydride is used in the production of plasticizers, polyester resins and alkyd paints. The Company evaluates performance and determines resource allocations based on a number of factors, the primary measure being operating profit or loss from operations. Operating profit does not include equity in earnings of affiliates, other income, interest expense, income taxes or operating costs of Koppers Holdings Inc. The accounting policies of the reportable segments are the same as those described in the summary of significant accounting policies. Intersegment transactions are eliminated in consolidation. The following table sets forth certain sales and operating data, net of all intersegment transactions, for the Company’s segments for the periods indicated: Year Ended December 31, 2017 2016 2015 (Dollars in millions) Revenues from external customers: Railroad and Utility Products and Services $ 512.6 $ 586.5 $ 657.0 Performance Chemicals 411.2 393.4 356.5 Carbon Materials and Chemicals 551.7 436.3 613.4 Total $ 1,475.5 $ 1,416.2 $ 1,626.9 Intersegment revenues: Performance Chemicals $ 6.7 $ 8.1 $ 8.7 Carbon Materials and Chemicals 79.6 90.2 86.7 Total $ 86.3 $ 98.3 $ 95.4 Depreciation and amortization expense: Railroad and Utility Products and Services (a) $ 11.8 $ 11.9 $ 14.2 Performance Chemicals 17.9 18.7 19.0 Carbon Materials and Chemicals (b) 20.1 22.3 25.8 Total $ 49.8 $ 52.9 $ 59.0 Operating profit (loss): Railroad and Utility Products and Services (c) $ 25.3 $ 52.5 $ 62.2 Performance Chemicals 71.4 63.5 39.0 Carbon Materials and Chemicals (d) 27.4 (23.6 ) (125.0 ) Corporate (e) (12.0 ) (6.0 ) (5.8 ) Total $ 112.1 $ 86.4 $ (29.6 ) Capital expenditures (including acquisitions): Railroad and Utility Products and Services $ 10.6 $ 11.2 $ 11.1 Performance Chemicals 15.4 7.9 5.8 Carbon Materials and Chemicals 39.7 29.5 37.6 Corporate 1.8 1.3 1.5 Total $ 67.5 $ 49.9 $ 56.0 (a) Excludes impairment charges of $1.9 million in 2015 for a wood treating facility in the United States. (b) Excludes impairment charges of $3.7, $3.5 and $12.8 million in 2017, 2016 and 2015, respectively, for CMC. (c) Includes asset retirement obligation and other restructuring costs of $1.6 million for the restructuring of two facilities in the United States in 2017. Includes asset retirement obligation and other restructuring costs of $6.9 million for the restructuring of three facilities in the United States in 2016. Includes gain on sale of the Company’s North American utility pole business of $3.2 million and restructuring costs of $5.7 million for a wood treating facility in the United States in 2015. (d) Includes plant closure costs of $14.6, $13.2 and $36.5 million in 2017, 2016 and 2015, respectively, for CMC. In the fourth quarter of 2015, the Company also recorded goodwill impairment charges of $67.2 million related to this business unit. (e) Operating loss for Corporate includes general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc., pension settlement losses, foreign exchange revaluation related to intercompany loans in connection with a legal reorganization of the Company and acquisition and acquisition-related integration costs. The following table sets forth tangible and intangible assets allocated to each of the Company’s segments as of the dates indicated: December 31, 2017 2016 (Dollars in millions) Segment assets: Railroad and Utility Products and Services $ 249.7 $ 264.2 Performance Chemicals 494.0 442.9 Carbon Materials and Chemicals 414.2 333.0 Segment assets 1,157.9 1,040.1 Cash and cash equivalents 0.7 0.0 Income tax receivable 1.7 3.8 Deferred taxes 29.4 32.5 Property, plant and equipment, net 5.2 4.9 Deferred charges 0.2 0.7 Other 5.1 5.5 Total $ 1,200.2 $ 1,087.5 Goodwill: Railroad and Utility Products and Services $ 10.5 $ 9.9 Performance Chemicals 177.7 176.5 Total $ 188.2 $ 186.4 Revenues and Long-lived Assets by Geographic Area Year Revenue Long-lived assets (Dollars in millions) United States 2017 $ 852.2 $ 479.5 2016 929.3 446.6 2015 991.2 460.3 Australasia 2017 312.8 131.4 2016 228.4 124.3 2015 280.9 132.9 Europe 2017 173.1 44.8 2016 140.2 31.9 2015 144.0 32.9 Other countries 2017 137.4 19.4 2016 118.3 19.5 2015 210.8 18.3 Total 2017 $ 1,475.5 $ 675.1 2016 $ 1,416.2 $ 622.3 2015 $ 1,626.9 $ 644.5 Revenues by geographic area in the above table are attributed by the destination country of the sale. Revenues from non-U.S. countries totaled $623.3 million in 2017, $486.9 million in 2016 and $635.7 million in 2015. Segment Revenues for Significant Product Lines Year Ended December 31, 2017 2016 2015 (Dollars in millions) Railroad and Utility Products and Services: Railroad crossties $ 326.7 $ 374.0 $ 422.0 Utility poles 36.5 34.5 52.4 Creosote 45.3 49.6 45.7 Rail joints 28.2 24.4 28.1 Railroad infrastructure services 34.8 43.4 42.7 Other products 41.1 60.6 66.1 512.6 586.5 657.0 Performance Chemicals: Wood preservative products 383.8 365.5 318.6 Other products 27.4 27.9 37.9 411.2 393.4 356.5 Carbon Materials and Chemicals: Carbon pitch 223.3 191.0 283.4 Phthalic anhydride 93.5 75.6 65.1 Creosote and carbon black feedstock 89.6 71.3 119.6 Other products 145.3 98.4 145.3 551.7 436.3 613.4 Total $ 1,475.5 $ 1,416.2 $ 1,626.9

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes Income Tax Provision Components of the Company’s income tax provision from continuing operations are as follows: Year Ended December 31, 2017 2016 2015 (Dollars in millions) Current: Federal $ 11.1 $ (1.9 ) $ (4.2 ) State 0.6 1.3 0.2 Foreign 15.7 13.3 16.0 Total current tax provision 27.4 12.7 12.0 Deferred: Federal 2.6 (1.6 ) (19.2 ) State (1.2 ) 0.5 3.0 Foreign 0.2 (0.2 ) 0.0 Total deferred tax provision (benefit) 1.6 (1.3 ) (16.2 ) Total income tax provision (benefit) $ 29.0 $ 11.4 $ (4.2 ) Income (loss) before income taxes for 2017, 2016 and 2015 included $81.6 million, $48.2 million and $(15.2) million, respectively, from foreign operations. On December 22, 2017, the Tax Cut and Jobs Act (“Tax Act”) was signed into law. The Tax Act significantly revises the U.S. corporate income tax system by, among other things, lowering the corporate income tax rate to 21 percent from 35 percent and imposing a one-time transition tax on certain unrepatriated earnings of foreign subsidiaries. Most of the Tax Act’s changes are applicable for tax years beginning after December 31, 2017. Changes in tax rates and tax laws and their impact on deferred taxes are accounted for in the period of legislative enactment. Shortly after the enactment of the Tax Act, the SEC staff issued Staff Accounting Bulletin 118, which allows a company to record a provisional amount when it does not have the necessary information available, prepared, or analyzed in reasonable detail to complete its accounting for the change in the tax law. The measurement period begins in the reporting period that includes the Tax Act’s enactment date and ends when the company has obtained, prepared and analyzed the information necessary to finalize its accounting, but cannot extend beyond one year from the enactment date. Accordingly, the Company has recorded a reasonable estimate of the effects on its existing deferred tax balances and the one-time transition tax and will continue to gather additional information related to estimates surrounding the measurement of the impact. Such additional analysis includes collecting and refining necessary data and interpreting additional guidance issued by the tax authorities and other standard-setting bodies. Any adjustments to the Company’s estimates may materially impact our income tax expense in the period in which the adjustments are Deferred tax assets and liabiliti es are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. However, the Company is still analyzing certain aspects of the Tax Act and is refining its calculations, which could potentially affect the measurement of these balances or potentially give rise to new deferred tax items. The Company estimated the impact of the corporate income tax rate reduction and recorded a provisional charge of $7.4 million for the year ended December The Tax Act imposes a o ne-time transition tax on . The Company estimated this one-time transition tax and recorded a provisional charge to income tax expense of $13.1 For tax years beginning after December 31, 2017, The Tax Act introduces new provisions for U.S. taxation of certain global intangible low-taxed income (“GILTI”) that imposes a minimum tax on earnings of a foreign corporation that are deemed to exceed a certain threshold return relative to the underlying business investment. Due to its complexity and a current lack of guidance on certain elements of the calculation of the tax, the Company is not yet able to determine whether it will adopt a policy to provide deferred tax on existing temporary differences that may result in a future GILTI tax, or treat the tax paid as a period expense in the year incurred. The provision for income taxes is reconciled with the federal statutory rate as follows: Year Ended December 31, 2017 2016 2015 Federal income tax rate 35.0 % 35.0 % 35.0 % State income taxes, net of federal tax benefit (1.6 ) (0.8 ) 2.3 Foreign earnings taxed at different rates (21.6 ) (10.1 ) (8.3 ) Transition tax from Tax Act 21.7 0.0 0.0 Deferred tax adjustments from Tax Act 12.3 0.0 0.0 Change in tax contingency reserves 2.2 6.5 1.5 Valuation allowance adjustments 0.9 (1.9 ) (13.0 ) Domestic production activities deduction 0.0 0.0 (0.6 ) Goodwill impairment 0.0 0.0 (10.9 ) Deferred tax adjustments 0.0 (0.2 ) 0.4 Other (0.8 ) 1.1 (1.1 ) 48.1 % 29.6 % 5.3 % As a result of the Tax Act and the one-time mandatory transition tax, all previously unremitted earnings for which a U.S. deferred tax liability had not been accrued have now been subject to U.S. tax. At December 31, 2017, there was approximately $398 million of such unremitted earnings. Substantially all unremitted earnings will remain indefinitely invested in our foreign subsidiaries for the foreseeable future. In the event these earnings are remitted as a dividend, they could be subject to taxation based on currency gains or losses, state taxes, and foreign withholding taxes. We estimate that we will not incur significant additional taxes on those potential remittances. Taxes Excluded from Net Income Attributable to Koppers The amount of income tax expense (benefit) included in comprehensive income (loss) but excluded from net income attributable to Koppers relating to adjustments to copper swap contracts is $3.5 million, $8.0 million, and $(1.2) million for the years ended December 31, 2017, 2016 and 2015, respectively. The amount of income tax expense included in comprehensive income (loss) but excluded from net income attributable to Koppers relating to adjustments to reflect the unfunded status of employee post-retirement benefit plans is $2.8 million, $2.0 million, and $0.6 million for the years ended December 31, 2017, 2016 and 2015, respectively. The amount of income tax expense included in shareholders’ equity but excluded from net income attributable to Koppers relating to the expense for restricted stock and employee stock options recognized differently for financial and tax reporting purposes is $0.4 million and $0.5 million for the years ended December 31, 2016 and 2015, respectively. The Company adopted ASU No. 2018-02, “Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” effective October 1, 2017. ASU 2018-02 requires a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the newly enacted federal corporate income tax rate. The amount of the reclassification is the difference between the tax-effected items that are included in accumulated other comprehensive income and were recorded at the historical 35 percent corporate income tax rate and those same items that are now recorded at the newly enacted 21 percent corporate income tax rate. This difference was $3.2 million for the year ended December 31, 2017 Deferred Tax Assets and Liabilities Deferred income taxes reflect the net tax effects of differences between the carrying amounts of assets and liabilities for financial reporting purposes and for income tax purposes. Significant components of the Company’s deferred tax assets and liabilities are as follows: December 31, 2017 2016 (Dollars in millions) Deferred tax assets: Federal and state tax loss carryforwards (expiring from 2018-2036) $ 21.2 $ 11.3 Tax credits 15.0 15.4 Reserves, including insurance, environmental and deferred revenue 14.3 22.3 Asset retirement obligations 11.9 12.0 Pension and other postretirement benefits obligations 10.8 19.2 Foreign tax loss carryforwards (expiring beginning in 2018) 9.3 10.1 Accrued employee compensation 6.3 8.9 Book/tax inventory accounting differences 1.5 3.5 Other 6.1 6.6 Valuation allowance (44.5 ) (40.2 ) Total deferred tax assets 51.9 69.1 Deferred tax liabilities: Tax over book depreciation and amortization 33.2 42.7 Gain on derivative contracts 7.0 4.2 Other 0.7 1.4 Total deferred tax liabilities 40.9 48.3 Net deferred tax assets $ 11.0 $ 20.8 A valuation allowance is necessary when it is more likely than not that a deferred tax asset will not be realized. Certain deferred tax assets reflected above are not expected to be realized and a valuation allowance has been provided for them. Valuation allowances are recorded to offset the following deferred tax assets: December 31, 2017 2016 State temporary differences, net operating losses and tax credits $ 18.7 $ 13.2 Federal foreign tax credits 13.8 14.3 Foreign temporary differences, net operating losses and capital losses 12.0 12.7 Total valuation allowances $ 44.5 $ 40.2 During 2017, the Company generated additional net operating losses in certain states which require each legal entity to file a separate return. As it is not expected that certain entities will generate future taxable income to realize the benefit of these losses, the related valuation allowance was increased by $5.5 million. Management evaluated the ability to realize the deferred tax assets that are related to our domestic operations, particularly in light of our domestic financial reporting losses. In assessing the need for a valuation allowance, we considered all positive and negative evidence related to the realization of our net deferred tax assets. This assessment considered, among other matters, the nature and severity of current and cumulative losses, forecasts of future profitability, the duration of statutory carryforward periods, and tax planning alternatives. Additionally, there were unusual or non-recurring charges that greatly attributed to these domestic losses. As a result, management has concluded that its domestic operations will generate sufficient income in periods when these deferred tax assets become deductible and that these deferred tax assets will be realized. Unrecognized Tax Benefits A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: December 31, 2017 2016 2015 (Dollars in millions) Balance at beginning of year $ 9.7 $ 7.7 $ 7.2 Additions based on tax provisions related to the current year 0.1 0.9 1.4 Additions for tax provisions of prior years 2.7 1.5 0.0 Reductions of tax provisions of prior years (3.4 ) 0.0 (0.7 ) Reductions as a result of a lapse of the applicable statute of limitations (0.4 ) (0.4 ) (0.2 ) Balance at end of year $ 8.7 $ 9.7 $ 7.7 As of December 31, 2017 and 2016, the total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate, was approximately $4.4 million and $5.7 million, respectively. The Company recognizes interest expense (income) and any related penalties from unrecognized tax benefits in income tax expense. For the years ended December 31, 2017, 2016, and 2015, the Company recognized $(0.6) million, $1.2 million and $(1.5) million, respectively, in interest and penalties. As of December 31, 2017 and 2016, the Company had accrued interest and penalties of approximately $3.6 million and $4.2 million, respectively. The Company believes that it is reasonably possible that the amount of unrecognized tax benefits will decrease in the next twelve months by approximately $4 million due to the expirations of certain foreign and state statutes of limitations and potential audit resolutions. the next twelve months. The Company and its subsidiaries file income tax returns in the U.S. federal jurisdiction, individual U.S. state jurisdictions and non-U.S. jurisdictions. With few exceptions, the Company is no longer subject to U.S. federal, U.S. state, or non-U.S. income tax examinations by tax authorities for years before 2013.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventories	11. Inventories Inventories as of December 31, 2017 and 2016 were as follows: December 31, 2017 2016 (Dollars in millions) Raw materials $ 173.6 $ 157.7 Work in process 11.2 14.2 Finished goods 98.4 103.6 283.2 275.5 Less revaluation to LIFO 46.3 46.8 Net $ 236.9 $ 228.7

Equity Investments

Equity Investments	12 Months Ended
	Dec. 31, 2017
Equity Method Investments And Joint Ventures [Abstract]
Equity Investments	12. Equity Investments The Company has no remaining investments in unconsolidated companies as of December 31, 2016. During 2016, the Company sold its ownership interest in TKK. See additional information regarding TKK in Note 5, “Related Party Transactions.” During 2015, the Company sold the assets of KSA Limited Partnership for $2.5 million to a third party resulting in a gain of $0.3 million. KSA Limited Partnership was a 50 percent-owned concrete crosstie operation. No dividends were paid for the three years ended December 31, 2017. Equity in losses for the years ended December 31, 2016 and 2015 were $1.0 million and $2.2 million, respectively.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Property, Plant and Equipment	13. Property, Plant and Equipment Property, plant and equipment as of December 31, 2017 and 2016 were as follows: December 31, 2017 2016 (Dollars in millions) Land $ 17.6 $ 17.0 Buildings 63.4 58.2 Machinery and equipment 756.6 716.0 $ 837.6 $ 791.2 Less accumulated depreciation 509.6 510.4 Net $ 328.0 $ 280.8 Depreciation expense, including impairment charges, for the years ended December 31, 2017, 2016 and 2015 amounted to $37.5 million, $41.6 million and $58.4 million, respectively. Impairments – Impairment charges for 2017, 2016 and 2015 were $3.7 million, $3.5 million and $14.7 million, respectively. In 2017 and 2016, impairment charges primarily related to the decision to discontinue naphthalene and coal tar distillation activities at CMC plants located in the United States. The 2015 impairment charges primarily related to the decision to discontinue coal tar distillation activities at CMC plants located in the United Kingdom and the United States. The remaining 2015 impairment charges were related to the RUPS wood treating plant in Green Spring, West Virginia.

Goodwill and Other Identifiable

Goodwill and Other Identifiable Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Other Identifiable Intangible Assets	14. Goodwill and Other Identifiable Intangible Assets The change in the carrying amount of goodwill attributable to each business segment for the years ended December 31, 2017 and December 31, 2016 was as follows: Railroad and Utility Products and Services Performance Chemicals Total (Dollars in millions) Balance at December 31, 2015 $ 9.9 $ 176.7 $ 186.6 Currency translation 0.0 (0.2 ) (0.2 ) Balance at December 31, 2016 $ 9.9 $ 176.5 $ 186.4 Currency translation 0.6 1.2 1.8 Balance at December 31, 2017 $ 10.5 $ 177.7 $ 188.2 Goodwill represents the excess of the cost over the fair value of acquired identifiable tangible and intangible assets and liabilities assumed from businesses acquired. Goodwill is tested for impairment at the reporting unit level annually in the fourth quarter and whenever events or circumstances indicate the carrying value may not be recoverable. The evaluation of goodwill impairment involves using either a qualitative or quantitative approach as outlined in ASC Topic 350. In the fourth quarters of 2017 and 2016, the Company determined that the estimated fair values substantially exceeded the carrying values of all the reporting units, and accordingly, there was no impairment of goodwill for the year ended December 31, 2017 and 2016, respectively. During the fourth quarter of 2015, the Company completed its annual goodwill impairment evaluation using the two-step quantitative analysis. In the first step of the analysis, the Company compared the estimated fair value of each reporting unit to its carrying value, including goodwill. The fair value of the reporting units was determined based on a weighting of income and market approaches. Since the carrying value of the CMC reporting unit exceeded the fair value, the Company performed the second step of the impairment analysis in order to determine the implied fair value of the reporting unit’s goodwill. The implied fair value of goodwill represents the excess of fair value of the reporting unit over the fair value amounts assigned to all of the assets and liabilities of the reporting unit as if it were to be acquired in a business combination and the current fair value of the reporting unit (as calculated in the first step) was the purchase price. Any amount remaining after this allocation represents the implied fair value of goodwill. The implied fair value of the respective reporting unit’s goodwill was then compared to the carrying value of the goodwill and any excess of carrying value over the implied fair value represents the non-cash impairment charge. The results of the second step analysis showed that the implied fair value of goodwill was zero for the CMC reporting unit. Therefore, in 2015, the Company recorded a goodwill impairment charge of $67.2 million for the CMC reporting unit. During the fourth quarter of 2015, the Company observed certain negative factors including a declining market capitalization, downsizing of the global aluminum markets and continued decline in spot and forward oil pricing. As noted elsewhere in this Form 10-K, the Company and its board of directors approved certain strategic changes for the CMC reporting unit during the fourth quarter of 2015 reflecting the current market environment. The aforementioned negative factors all severely impacted the outlook and corresponding fair value for the Company’s CMC reporting unit and were the primary factors for the goodwill impairment charge recorded during the fourth quarter of 2015. As a result of the goodwill impairment charge, there is no goodwill remaining for the CMC reporting unit as of December 31, 2015. For purposes of the income approach, fair value was determined based on the present value of estimated future cash flows, discounted at an appropriate risk-adjusted rate (DCF analysis). The Company made assumptions about the amount and timing of future expected cash flows, terminal value growth rates and appropriate discount rates. The amount and timing of future cash flows within the Company’s DCF analysis was based on its most recent operational budgets, long range strategic plans and other estimates. A one half of one percent perpetual growth rate was used to calculate the value of cash flows beyond the last projected period in the Company’s DCF analysis for the CMC reporting unit and reflects its best estimates for stable, perpetual growth of its reporting unit. Actual results may differ from those assumed in the Company’s forecasts. The Company used estimates of market participant weighted average cost of capital as a basis for determining the discount rate of 14 percent applied to the CMC reporting unit’s future expected cash flows, adjusted for risks and uncertainties inherent in the chemical industry and in its internally developed forecasts. The market approach is based upon an analysis of valuation metrics for companies comparable to the reporting unit. The fair value for the CMC reporting unit was estimated using an appropriate valuation multiple, as well as estimated normalized earnings and an estimated control premium. In order to further validate the reasonableness of the estimated fair values of the reporting units as of the valuation date in the fourth quarter of 2015, a reconciliation of the aggregate fair values of all reporting units to the Company’s market capitalization was performed using a reasonable control premium. Goodwill impairment tests in years prior to December 31, 2015 indicated that goodwill was not impaired for any of the Company’s reporting units. Accumulated impairment losses totaled $67.2 million as of December 31, 2017 and 2016. The Company’s identifiable intangible assets with finite lives are being amortized over their estimated useful lives and are summarized below: December 31, 2017 2016 Estimated life in years Weighted average remaining life in years Gross Carrying Amount Accumulated Amortization Net Gross Carrying Amount Accumulated Amortization Net (Dollars in millions) Customer contracts 9 to 18 12.2 $ 154.7 $ 43.9 $ 110.8 $ 152.5 $ 33.6 $ 118.9 Technology 4 to 12 4.0 26.8 12.5 14.3 26.7 8.8 17.9 Trademarks 4 to 7 4.0 6.5 2.7 3.8 6.1 1.9 4.2 Supply contracts 10 2.2 2.5 2.0 0.5 2.2 1.5 0.7 Non-compete agreements 12 6.8 1.4 1.2 0.2 1.3 1.1 0.2 Favorable lease agreements 3 0.0 0.7 0.7 0.0 0.6 0.6 0.0 Total 11.1 $ 192.6 $ 63.0 $ 129.6 $ 189.4 $ 47.5 $ 141.9 In 2017, the gross carrying value of identifiable intangible assets increased by $2.7 million due to foreign currency translation. Total amortization expense related to these identifiable intangible assets was $14.6 million, $14.8 million and $15.3 million for the years ended December 31, 2017, 2016 and 2015, respectively. Estimated amortization expense for the next five years is summarized below: Estimated annual amortization (Dollars in millions) 2018 $ 14.5 2019 14.5 2020 14.2 2021 12.3 2022 9.6

Pensions and Post-Retirement Be

Pensions and Post-Retirement Benefit Plans	12 Months Ended
	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Pensions and Post-Retirement Benefit Plans	15. Pensions and Post-Retirement Benefit Plans The Company and its subsidiaries maintain a number of defined benefit and defined contribution plans to provide retirement benefits for employees in the U.S., as well as employees outside the U.S. These plans are maintained and contributions are made in accordance with the Employee Retirement Income Security Act of 1974 (“ERISA”), local statutory law or as determined by the board of directors. The defined benefit pension plans generally provide benefits based upon years of service and compensation. Pension plans are funded except for three domestic non-qualified defined benefit pension plans for certain key executives. In the U.S., all qualified and two of the non-qualified defined benefit pension plans for salaried and hourly employees have been closed to new participants and have been frozen. Accordingly, these pension plans no longer accrue additional years of service or recognize future increases in compensation for benefit purposes. The defined contribution plans generally provide retirement assets to employee participants based upon employer and employee contributions to the participant’s individual investment account. The Company also provides retiree medical insurance coverage to certain U.S. employees and a life insurance benefit to most U.S. employees. For salaried employees, the retiree medical and retiree insurance plans have been closed to new participants. In the fourth quarter of 2017, the Company offered a cash lump sum or annuity buyout to its terminated deferred vested participants in its U.S. defined benefit pension plan. Approximately 100 participants elected either a lump sum payout or annuity from a third-party provider. The total dollar amount paid out of our defined benefit plan assets was $3.1 million and the Company recorded a pension settlement charge of $1.2 million related to this transaction. In the third quarter of 2017, the Company completed an irrevocable transaction with an insurance company to annuitize approximately $31.3 million of retiree pension obligations in its U.S. qualified defined benefit pension plan for a selected group of retirees. The transaction was funded by transferring a similar amount of assets from the pension plan to the insurance company. Subsequent to this transfer, the insurance company has assumed all remaining pension obligations associated with these retirees. This represents approximately 18 percent of the plan’s discounted pension obligation as of that date and the Company recorded a pension settlement loss of $8.8 million in the third quarter of 2017. In the third quarter of 2016, the Company offered a cash lump sum or annuity buyout to its terminated deferred vested participants in its U.S. defined benefit pension plan. Approximately 375 participants elected either a lump sum payout or annuity from a third-party provider. The total dollar amount paid out of our defined benefit plan assets was $13.9 million and the Company recorded a pension settlement charge of $4.4 million for the year ended December 31, 2016. Expense related to defined contribution plans totaled $8.9 million, $7.8 million and $6.0 million for the years ended December 31, 2017, 2016 and 2015, respectively. Net periodic pension costs for 2017, 2016 and 2015 were as follows: Year Ended December 31, Pension Benefits Other Benefits 2017 2016 2015 2017 2016 2015 (Dollars in millions) Service cost $ 2.0 $ 1.7 $ 2.0 $ 0.1 $ 0.1 $ 0.1 Interest cost 9.0 11.0 10.9 0.4 0.4 0.4 Expected return on plan assets (9.6 ) (10.5 ) (12.0 ) 0.0 0.0 0.0 Amortization of prior service cost 0.0 0.0 (0.3 ) 0.0 0.0 (0.1 ) Amortization of net loss 1.9 2.2 6.6 (0.2 ) (0.4 ) (0.3 ) Settlements and curtailments 10.0 4.4 (0.8 ) 0.0 0.0 0.0 Net periodic benefit cost $ 13.3 $ 8.8 $ 6.4 $ 0.3 $ 0.1 $ 0.1 Net periodic pension cost is expected to be recognized from the amortization of net loss and is estimated to total $1.4 million for all plans in 2018. The change in the funded status of the pension and postretirement plans as of December 31, 2017 and December 31, 2016 is as follows: December 31, Pension Benefits Other Benefits 2017 2016 2017 2016 (Dollars in millions) Change in benefit obligation: Benefit obligation at beginning of year $ 243.6 $ 257.5 $ 10.0 $ 9.4 Service cost 2.0 1.7 0.1 0.1 Interest cost 9.0 11.0 0.4 0.4 Actuarial losses 7.3 10.7 1.5 1.0 Settlements (36.9 ) (13.9 ) 0.0 0.0 Currency translation 5.5 (9.9 ) 0.0 0.0 Benefits paid (11.4 ) (13.5 ) (0.9 ) (0.9 ) Benefit obligation at end of year 219.1 243.6 11.1 10.0 Change in plan assets: Fair value of plan assets at beginning of year 200.9 212.4 0.0 0.0 Actual return on plan assets 19.5 20.8 0.0 0.0 Employer contribution 11.2 4.5 0.9 0.9 Settlements (36.9 ) (13.9 ) 0.0 0.0 Currency translation 5.5 (9.4 ) 0.0 0.0 Benefits paid (11.4 ) (13.5 ) (0.9 ) (0.9 ) Fair value of plan assets at end of year 188.8 200.9 0.0 0.0 Funded status of the plan $ (30.3 ) $ (42.7 ) $ (11.1 ) $ (10.0 ) Amounts recognized in the balance sheet consist of: Noncurrent assets $ 7.0 $ 0.8 $ 0.0 $ 0.0 Current liabilities 1.1 1.1 1.0 0.8 Noncurrent liabilities 36.2 42.4 10.1 9.2 Pension plans with projected benefit obligations in excess of plan assets: Benefit obligation $ 159.9 $ 238.7 Fair value of plan assets 122.6 195.3 Pension plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligation $ 159.6 $ 238.5 Fair value of plan assets 122.6 195.3 The measurement date for all pension and postretirement assets and obligations is December 31 for each respective year. The accumulated benefit obligation for all defined benefit pension plans as of December 31, 2017 and 2016 was $218.7 million and $243.3 million, respectively. Expected Contributions for the 2018 Fiscal Year The expected contributions by the Company for 2018 are estimated to be $4.4 million for pension plans and $1.0 million for other benefit plans. Projected Benefit Payments Benefit payments for pension benefits, which are primarily funded by the pension plan assets, and other benefits, which are funded by general corporate assets and reflecting future expected service as appropriate, are expected to be paid as follows: Pension Benefits Other Benefits (Dollars in millions) 2018 $ 11.1 $ 1.0 2019 11.0 1.0 2020 11.3 0.9 2021 11.5 0.8 2022 11.7 0.7 Next five years 64.0 3.2 Weighted-Average Assumptions as of December 31 December 31, Pension Benefits Other Benefits 2017 2016 2017 2016 Discount rate 3.51 % 4.09 % 3.88 % 4.53 % Expected return on plan assets 4.62 5.10 Rate of compensation increase 3.50 3.50 Initial medical trend rate 6.10 6.30 Basis for the Selection of the Long-Term Rate of Return on Assets The long-term rate of return on assets assumption was determined by using the plan’s asset allocation as described in the plan’s investment policy and modeling a distribution of compound average returns over a time horizon. The model uses asset class return, variance, and correlation assumptions to produce the expected return. The return assumptions used forward looking gross returns influenced by the current bond yields, corporate bond spreads and equity risk premiums based on current market conditions. In general, the long-term rate of return is the sum of the portion of total assets in each asset class multiplied by the expected return for that class, adjusted for expected expenses to be paid from the assets. To develop the expected long-term rate of return on assets assumption, the Company considered the historical returns and the future expectations for returns for each asset class, as well as the target asset allocation of the pension portfolio. Investment Strategy The weighted average asset allocation for the Company’s pension plans at December 31 by asset category is as follows: December 31, 2017 2016 Debt securities 64 % 71 % Equity securities 30 24 Other 6 5 100 % 100 % The Company’s investment strategy for its pension plans is to maintain an adequate level of diversification, to reduce interest rate and market risk and to provide adequate liquidity to meet immediate and future benefit payment requirements. The The investment valuation policy of the Company is to value investments at fair value. Most of the assets are invested in pooled or commingled investment vehicles. The Company’s interest in these investment vehicles is expressed as a unit of account with a value per unit that is the result of the accumulated values of the underlying investments. Equity securities held within these investment vehicles are typically priced on a daily basis using the closing market price from the exchange through which the security is traded. Debt securities held within these investment vehicles are typically priced on a daily basis by independent pricing services. The fair value of real estate investments is either priced through a listing on an exchange or are subject to periodic appraisals. The following table sets forth by level, the Company’s pension plan assets at fair value, within the fair value hierarchy, as of December 31, 2017 and December 31, 2016: As of December 31, 2017 Quoted prices in active Significant Significant markets for observable unobservable identical assets inputs inputs (Level 1) (Level 2) (Level 3) Total (Dollars in millions) U.S. equity securities $ 18.6 $ 12.7 $ 0.0 $ 31.3 International equity securities 15.0 10.2 0.0 25.2 U.S. debt securities 21.4 53.0 2.5 76.9 International debt securities 7.5 34.8 1.0 43.3 Real estate and other investments 0.5 0.8 8.3 9.6 Cash and cash equivalents 0.0 2.5 0.0 2.5 $ 63.0 $ 114.0 $ 11.8 $ 188.8 As of December 31, 2016 Quoted prices in active Significant Significant markets for observable unobservable identical assets inputs inputs (Level 1) (Level 2) (Level 3) Total (Dollars in millions) U.S. equity securities $ 12.3 $ 13.2 $ 0.0 $ 25.5 International equity securities 12.6 10.9 0.0 23.5 U.S. debt securities 29.7 75.2 3.2 108.1 International debt securities 8.3 24.3 1.1 33.7 Real estate and other investments 0.0 0.5 5.7 6.2 Cash and cash equivalents 0.0 3.9 0.0 3.9 $ 62.9 $ 128.0 $ 10.0 $ 200.9 The table below sets forth a summary of changes in the fair value of the Level 3 pension plans’ assets for the year ended December 31, 2017: As of December 31, 2017 Other Investments Debt Securities (Dollars in millions) Balance at beginning of year $ 5.7 $ 4.3 Purchases, sales, issuances and settlements 1.9 (1.4 ) Realized and unrealized gains 0.7 0.6 Balance at the end of year $ 8.3 $ 3.5 The amount of total gains during the period attributable to the change in unrealized gains relating to Level 3 net assets still held at the reporting date $ 0.2 $ 0.1 Health Care Cost Trend Rates The 2018 initial health care cost trend rate is assumed to be 6.3 percent and is assumed to decrease gradually to 4.5 percent in 2037 and remain at that level thereafter. The assumed health care cost trend rate has a significant effect on the amounts reported for other postretirement benefit liability. A one-percentage-point change in the assumed health care cost trend rate would have the following effects: 1% Increase 1% Decrease (Dollars in millions) Increase (decrease) from change in health care cost trend rates: Postretirement benefit expense $ 0.0 $ 0.0 Postretirement benefit liability 0.2 (0.1 ) Incentive Plan The Company has short-term management incentive plans that pay cash bonuses if certain Company performance goals are met. The charge to operating expense for these plans was $11.2 million in 2017, $10.4 million in 2016 and $9.2 million in 2015.

Debt

Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt	16. Debt Debt as of December 31, 2017 and 2016 was as follows: December 31, Weighted Average Interest Rate Maturity 2017 2016 Revolving Credit Facility 4.01 % 2022 $ 155.0 $ 100.1 Term Loan 0.0 232.5 Construction and other loans 4.80 % 2020 33.7 40.4 Senior Notes due 2025 6.00 % 2025 500.0 0.0 Senior Notes due 2019 0.0 298.1 Total debt 688.7 671.1 Less short-term debt and current maturities of long-term debt 11.4 42.6 Less unamortized debt issuance costs 11.7 8.7 Long-term debt $ 665.6 $ 619.8 Events subsequent to December 31, 2017 In February 2018, the Company amended its $400.0 million Revolving Credit Facility to increase its capacity to $600.0 million. The interest rate on the amended Revolving Credit Facility is variable and is based on LIBOR. Terms under the amended Revolving Credit Facility are substantially consistent with the original Revolving Credit Facility. Senior Notes due 2025 In January 2017, Koppers Inc. completed a private placement offering of $500.0 million 6.00 percent Senior Notes due 2025. Koppers Inc. used the proceeds from the offering of the 2025 Notes to repay its outstanding term loan and to fund a tender offer to repurchase its senior notes due 2019. The 2025 Notes are our 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 February 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 In February 2017, the Company entered into a $400.0 million senior secured Revolving Credit Facility. The maturity date is February 2022 and the interest rate is variable and is based on LIBOR. 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 December 31, 2017, the Company had $203.3 million of unused revolving credit availability for working capital purposes after restrictions from certain letter of credit commitments and other covenants. As of December 31, 2017, $41.7 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 the 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 KJCC entered into two committed loan facility agreements for a combined commitment of RMB 265 million or approximately $44 million. The third-party bank provided facility has a commitment amount of RMB 198.8 million and the other committed facility of RMB 66.2 million is provided by the 25-percent non-controlling shareholder in KJCC. Borrowings under the third-party bank facility 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. Debt Maturities and Deferred Financing Costs At December 31, 2017 the aggregate debt maturities for the next five years are as follows: (Dollars in millions) 2018 $ 11.4 2019 3.0 2020 19.3 2021 0.0 2022 155.0 Thereafter 500.0 Total debt $ 688.7 Unamortized debt issuance costs (net of accumulated amortization of $1.8 million and $12.0 million at December 31, 2017 and 2016, respectively) were $11.7 million and $8.7 million at December 31, 2017 and 2016, respectively, and are included as a deduction from the carrying amount of long-term debt.

Leases

Leases	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Leases	17. Leases Future minimum commitments for operating leases having non-cancelable lease terms in excess of one year are as follows: (Dollars in millions) 2018 $ 43.7 2019 25.3 2020 20.6 2021 16.4 2022 15.2 Thereafter 50.2 Total $ 171.4 Operating lease expense for 2017, 2016 and 2015 was $50.4 million, $50.3 million and $46.4 million, respectively.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	18. 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 30 months and the Company has hedged certain volumes of copper through December 2019. The Company enters into foreign currency forward contracts to manage foreign currency risk associated with the Company’s receivable and payable balances in addition to foreign-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. 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 (loss) 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 not material for any period presented. For those commodity swaps which are not designated as cash flow hedges, the fair value of the commodity 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 December 31, 2017 and December 31, 2016, the Company had outstanding copper swap contracts of the following amounts: Units Outstanding (in Pounds) Net Fair Value - Asset (Liability) December 31, December 31, 2017 2016 2017 2016 (Amounts in millions) Cash flow hedges 37.8 42.6 $ 25.5 $ 10.6 Not designated as hedges 11.3 6.5 4.5 1.0 Total 49.1 49.1 $ 30.0 $ 11.6 As of December 31, 2017 and December 31, 2016, the fair value of the outstanding copper swap contracts is recorded in the balance sheet as follows: December 31, 2017 2016 (Dollars in millions) Other current assets $ 21.8 $ 12.5 Other assets 8.2 0.0 Accrued liabilities 0.0 (0.9 ) Net asset on balance sheet $ 30.0 $ 11.6 Accumulated other comprehensive gain, net of tax $ 15.8 $ 6.9 In the next twelve months the Company estimates that $13.3 million of unrealized gains, net of tax, related to commodity price hedging will be reclassified from other comprehensive income (loss) into earnings. See the Consolidated Statement of Comprehensive Income and Consolidated Statement of Shareholders’ Equity for amounts recorded in other comprehensive income and for amounts reclassified from accumulated other comprehensive income into net income for the periods specified below. For the years ended December 31, 2017 and 2016, the following amounts were recognized in earnings related to copper swap contracts: Year Ended December 31, 2017 2016 (Dollars in millions) Gain (loss) from ineffectiveness of cash flow hedges $ 5.6 $ (0.4 ) Gain from contracts not designated as hedges 3.5 1.7 Net $ 9.1 $ 1.3 As of December 31, 2017, the Company has $4.2 million of U.S. dollar-denominated forward contracts related to foreign currency, which are designated as cash flow hedges. The fair value of these forward contracts, which expire in the next twelve months, is $0.3 million which has been credited to other comprehensive income for the year ended December 31, 2017. 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 Consolidated Statement of Operations. As of December 31, 2017, the Company has outstanding foreign currency forward contracts 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 December 31, 2016, the Company has outstanding currency forward contracts with a net fair value totaling $1.0 million, consisting of a gross derivative liability of $0.9 million (recognized in accrued liabilities in the balance sheet) and a gross derivative asset of $1.9 million (recognized in other current assets in the balance sheet). As of December 31, 2017 and 2016, the net currency units outstanding were: December 31, 2017 2016 (In millions) British Pounds GBP 7.0 GBP 7.3 New Zealand Dollars NZD 15.5 NZD 15.5 United States Dollars USD 12.5 USD 24.7 Canadian Dollars CAD 2.5 CAD 0.3

Common Stock and Senior Convert

Common Stock and Senior Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2017
Text Block [Abstract]
Common Stock And Senior Convertible Preferred Stock	19. Common Stock and Senior Convertible Preferred Stock Changes in senior convertible preferred stock, common stock and treasury stock for the three years ended December 31, 2017 are as follows: December 31, 2017 2016 2015 (Shares in thousands) Senior Convertible Preferred Stock: Balance at beginning and end of year 0 0 0 Common Stock: Balance at beginning of year 22,141 22,016 21,938 Issued for employee stock plans 243 125 78 Balance at end of year 22,384 22,141 22,016 Treasury Stock: Balance at beginning of year (1,476 ) (1,459 ) (1,443 ) Shares repurchased (130 ) (17 ) (16 ) Balance at end of year (1,606 ) (1,476 ) (1,459 )

Commitments and Contingent Liab

Commitments and Contingent Liabilities	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities	20. 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 87 plaintiffs in 48 cases pending as of December 31, 2017 compared to 99 plaintiffs in 55 cases as of December 31, 2016. As of December 31, 2017, there are 47 cases pending in state court in Pennsylvania, and one case pending in state court in Tennessee. The plaintiffs in all 48 pending cases seek to recover compensatory damages. Plaintiffs in 44 of those cases also seek to recover punitive damages. The plaintiffs in the 47 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. Gainesville . Koppers Inc. operated a utility pole treatment plant in Gainesville, Florida from December 29, 1988 until its closure in 2009. The property upon which the utility pole treatment plant was located was sold by Koppers Inc. to Beazer East in 2010. In November 2010, a putative class action complaint was filed by residential real property owners located in a neighborhood west of and immediately adjacent to the former utility pole treatment plant in Gainesville. The plaintiffs alleged that chemicals and contaminants from the Gainesville plant contaminated their properties, caused property damage (diminution in value) and placed residents and owners of the putative class properties at an elevated risk of exposure to and injury from the chemicals at issue. The district court denied the plaintiffs motion for class certification and the plaintiffs filed an amended complaint on behalf of five individual plaintiffs in August 2017. In December 2017, the parties have agreed to resolve this litigation with the five remaining individual plaintiffs for an immaterial amount, and the parties have filed a joint stipulation for dismissal. 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. 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 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 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 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 December 31, 2017, the Company’s estimated environmental remediation liability for these acquired sites totals $4.9 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 December 31, 2017, the Company’s estimated environmental remediation liability for these acquired sites totals $2.8 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 $2.6 million as of December 31, 2017. Environmental Reserves Rollforward . The following table reflects changes in the accrued liability for environmental matters, of which $5.1 million and $5.2 million are classified as current liabilities at December 31, 2017 and 2016: Year Ended December 31, 2017 2016 (Dollars in millions) Balance at beginning of year $ 12.9 $ 19.8 Expense 3.2 1.5 Reversal of reserves (0.7 ) (1.0 ) Cash expenditures (1.8 ) (6.3 ) Divestitures 0.0 (0.3 ) Currency translation 0.3 (0.8 ) Balance at end of period $ 13.9 $ 12.9

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	21. Selected Quarterly Financial Data (Unaudited) The following is a summary of the quarterly results of operations for the years ended December 31, 2017 and 2016: Year Ended December 31, 2017 1 st 2 nd 3 rd 4 th Fiscal Year (Dollars in millions, except per share amounts) Statement of operations data: Net sales $ 346.6 $ 378.0 $ 384.8 $ 366.1 $ 1,475.5 Operating profit 27.6 37.6 34.7 12.2 112.1 Income (loss) from continuing operations (a) 4.7 20.9 20.0 (14.3 ) 31.3 Net income (loss) (a) 4.6 19.8 19.9 (13.8 ) 30.5 Net income (loss) attributable to Koppers (a) 4.4 19.7 19.8 (14.8 ) 29.1 Common stock data: Earnings (loss) per common share attributable to Koppers common shareholders: (a)(b) Basic – Continuing operations $ 0.21 $ 1.00 $ 0.96 $ (0.73 ) $ 1.44 Discontinued operations 0.00 (0.06 ) 0.00 0.02 (0.04 ) Earnings (loss) per basic common share $ 0.21 $ 0.94 $ 0.96 $ (0.71 ) $ 1.40 Diluted – Continuing operations $ 0.20 $ 0.95 $ 0.91 $ (0.73 ) $ 1.36 Discontinued operations 0.00 (0.05 ) 0.00 0.02 (0.04 ) Earnings (loss) per diluted common share $ 0.20 $ 0.90 $ 0.91 $ (0.71 ) $ 1.32 Price range of common stock: High $ 45.85 $ 44.80 $ 46.55 $ 51.80 $ 51.80 Low 39.10 33.90 35.17 45.75 33.90 Year Ended December 31, 2016 1 st 2 nd 3 rd 4 th Fiscal Year (Dollars in millions, except per share amounts) Statement of operations data: Net sales $ 346.8 $ 385.1 $ 371.1 $ 313.2 $ 1,416.20 Operating profit 7.8 32.0 27.7 18.9 86.4 Income (loss) from continuing operations (2.4 ) 11.3 12.0 6.2 27.1 Net income (loss) (1.8 ) 11.3 11.9 6.3 27.7 Net income (loss) attributable to Koppers (1.3 ) 12.1 12.1 6.4 29.3 Common stock data: Earnings (loss) per common share attributable to Koppers common shareholders: (b) Basic – Continuing operations $ (0.09 ) $ 0.58 $ 0.59 $ 0.31 $ 1.39 Discontinued operations 0.03 0.00 0.00 0.00 0.03 Earnings (loss) per basic common share $ (0.06 ) $ 0.58 $ 0.59 $ 0.31 $ 1.42 Diluted – Continuing operations $ (0.09 ) $ 0.57 $ 0.58 $ 0.30 $ 1.36 Discontinued operations 0.03 0.00 0.00 0.00 0.03 Earnings (loss) per diluted common share $ (0.06 ) $ 0.57 $ 0.58 $ 0.30 $ 1.39 Price range of common stock: High $ 23.43 $ 31.35 $ 33.71 $ 42.70 $ 42.70 Low 13.58 21.38 28.54 31.28 13.58 (a) Income tax expense for the fourth quarter of 2017 was increased by $20.5 million due to the impact of the Tax Cuts and Jobs Act which was signed into law on December 22, 2017. (b) The cumulative sum of quarterly basic and diluted net income per share amounts may not equal total basic and diluted net income per share amounts for the year due to differences in weighted average and equivalent shares outstanding for each of the periods presented.

Subsidiary Guarantor Informatio

Subsidiary Guarantor Information for Koppers Inc. 2025 Notes and Shelf Registration	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Subsidiary Guarantor Information for Koppers Inc. 2025 Notes and Shelf Registration	22. Subsidiary Guarantor Information for Koppers Inc. 2025 Notes and Shelf Registration 2025 Notes On January 25, 2017, Koppers Inc. issued $500.0 million principal value of Senior Notes due 2025 (the “2025 Notes”). Koppers Holdings and each of Koppers Inc.’s 100 percent-owned material domestic subsidiaries other than Koppers Assurance, Inc. fully and unconditionally guarantee the payment of principal and interest on the 2025 Notes. The domestic guarantor subsidiaries include Koppers World-Wide Ventures Corporation, Koppers Delaware, Inc., Koppers Concrete Products, Inc., Concrete Partners, Inc., Koppers Performance Chemicals Inc., Koppers Railroad Structures Inc., Koppers NZ, LLC, Koppers-Nevada Limited Liability Company, Wood Protection LP, Wood Protection Management LLC and Koppers Asia 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 guarantee of a guarantor subsidiary will be automatically and unconditionally released and discharged in the event of: any sale of the capital stock or substantially all of the assets of the guarantor subsidiary; the designation of the guarantor subsidiary as an unrestricted subsidiary in accordance with the indenture governing the 2025 Notes; and the legal defeasance, covenant defeasance or satisfaction and discharge of the indenture governing the 2025 Notes. 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. and/or each of Koppers Inc.’s 100 percent-owned material domestic subsidiaries other than Koppers Assurance, Inc. The domestic guarantor subsidiaries are the same as those which guarantee the 2025 Notes. 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 supplement 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) we are in pro forma compliance with our fixed charge coverage ratio covenant after giving effect to such dividend. The indenture governing the 2025 Notes restrict Koppers Inc.’s ability to finance our 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 we refer 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 December 31, 2017, Koppers Inc.’s assets exceeded its liabilities by $100.1 million. The amount of restricted net assets unavailable for distribution to Koppers Holdings Inc. by Koppers Inc. totals $31 million as of December 31, 2017. Cash dividends paid to Koppers Holdings Inc. by its subsidiaries totaled $3.8 million, $1.2 million and $6.5 million for the years ended December 31, 2017, 2016 and 2015, respectively. Condensed Consolidating Statement of Comprehensive Income (Loss) For the Year Ended December 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 590.6 $ 344.9 $ 623.3 $ (83.3 ) $ 1,475.5 Cost of sales including depreciation and amortization 0.0 570.9 235.0 496.3 (82.1 ) 1,220.1 Loss on pension settlement 0.0 10.0 0.0 0.0 0.0 10.0 Selling, general and administrative 1.9 47.7 43.3 40.4 0.0 133.3 Operating (loss) profit (1.9 ) (38.0 ) 66.6 86.6 (1.2 ) 112.1 Other income (loss) 0.0 0.5 2.4 2.3 (1.2 ) 4.0 Equity income of subsidiaries 30.3 103.8 64.7 0.0 (198.8 ) 0.0 Interest (income) expense 0.0 39.0 0.0 4.7 (1.2 ) 42.5 Loss on extinguishment 0.0 13.3 0.0 0.0 0.0 13.3 Income taxes (0.7 ) (16.4 ) 30.0 16.2 (0.1 ) 29.0 Income from continuing operations 29.1 30.4 103.7 68.0 (199.9 ) 31.3 Discontinued operations 0.0 0.0 0.0 (0.8 ) 0.0 (0.8 ) Noncontrolling interests 0.0 0.0 0.0 1.4 0.0 1.4 Net income attributable to Koppers $ 29.1 $ 30.4 $ 103.7 $ 65.8 $ (199.9 ) $ 29.1 Comprehensive income (loss) attributable to Koppers $ 60.7 $ 61.8 $ 132.8 $ 89.2 $ (283.8 ) $ 60.7 Condensed Consolidating Statement of Comprehensive (Loss) Income For the Year Ended December 31, 2016 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 660.7 $ 350.6 $ 504.7 $ (99.8 ) $ 1,416.2 Cost of sales including depreciation and amortization 0.0 637.4 252.3 412.4 (101.2 ) 1,200.9 Gain on sale of business 0.0 0.0 0.0 (2.1 ) 0.0 (2.1 ) Loss on pension settlement 0.0 4.4 0.0 0.0 0.0 4.4 Selling, general and administrative 1.9 43.3 38.2 43.2 0.0 126.6 Operating (loss) profit (1.9 ) (24.4 ) 60.1 51.2 1.4 86.4 Other income (loss) 0.0 0.3 4.1 0.3 (1.8 ) 2.9 Equity income of subsidiaries 30.6 79.1 35.9 0.0 (145.6 ) 0.0 Interest (income) expense 0.0 47.6 0.0 5.0 (1.8 ) 50.8 Income taxes (0.6 ) (23.2 ) 22.2 13.0 0.0 11.4 Income from continuing operations 29.3 30.6 77.9 33.5 (144.2 ) 27.1 Discontinued operations 0.0 0.0 0.0 0.6 0.0 0.6 Noncontrolling interests 0.0 0.0 0.0 (1.6 ) 0.0 (1.6 ) Net income attributable to Koppers $ 29.3 $ 30.6 $ 77.9 $ 35.7 $ (144.2 ) $ 29.3 Comprehensive income (loss) attributable to Koppers $ 40.5 $ 41.3 $ 85.0 $ 29.6 $ (155.9 ) $ 40.5 Condensed Consolidating Statement of Comprehensive (Loss) Income For the Year Ended December 31, 2015 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 791.1 $ 335.6 $ 600.9 $ (100.7 ) $ 1,626.9 Cost of sales including depreciation and amortization 0.0 771.7 233.2 562.4 (99.4 ) 1,467.9 Gain on sale of business 0.0 (3.2 ) 0.0 0.0 0.0 (3.2 ) Goodwill impairment 0.0 43.1 24.1 0.0 0.0 67.2 Selling, general and administrative 1.9 41.3 37.8 43.6 0.0 124.6 Operating (loss) profit (1.9 ) (61.8 ) 40.5 (5.1 ) (1.3 ) (29.6 ) Other income (loss) 0.0 0.5 4.1 (2.4 ) (2.0 ) 0.2 Equity income of subsidiaries (70.8 ) 0.9 (27.9 ) 0.0 97.8 0.0 Interest expense 0.0 45.8 0.0 6.9 (2.0 ) 50.7 Income taxes (0.7 ) (35.4 ) 15.8 16.4 (0.3 ) (4.2 ) (Loss) income from continuing operations (72.0 ) (70.8 ) 0.9 (30.8 ) 96.8 (75.9 ) Discontinued operations 0.0 0.0 0.0 (0.1 ) 0.0 (0.1 ) Noncontrolling interests 0.0 0.0 0.0 (4.0 ) 0.0 (4.0 ) Net income attributable to Koppers $ (72.0 ) $ (70.8 ) $ 0.9 $ (26.9 ) $ 96.8 $ (72.0 ) Comprehensive income (loss) attributable to Koppers $ (91.5 ) $ (90.3 ) $ (18.1 ) $ (41.8 ) $ 150.2 $ (91.5 ) 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 Balance Sheet December 31, 2016 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) ASSETS Cash and cash equivalents $ 0.0 $ 0.0 $ 0.0 $ 20.8 $ 0.0 $ 20.8 Receivables, net 0.0 50.8 25.4 64.4 0.0 140.6 Affiliated receivables 0.7 34.8 32.2 15.4 (83.1 ) 0.0 Inventories, net 0.0 106.6 23.9 99.0 (0.8 ) 228.7 Other current assets 0.0 5.1 13.4 29.2 0.3 48.0 Total current assets 0.7 197.3 94.9 228.8 (83.6 ) 438.1 Equity investments 29.9 697.4 195.4 0.0 (922.7 ) 0.0 Property, plant and equipment, net 0.0 126.7 39.6 114.5 0.0 280.8 Goodwill 0.0 0.8 153.1 32.5 0.0 186.4 Intangible assets, net 0.0 7.9 107.1 26.9 0.0 141.9 Deferred tax assets 0.0 29.7 (8.4 ) 5.8 0.0 27.1 Affiliated loan receivables 0.0 36.9 205.3 21.9 (264.1 ) 0.0 Other assets 0.0 5.5 6.1 1.6 0.0 13.2 Total assets $ 30.6 $ 1,102.2 $ 793.1 $ 432.0 $ (1,270.4 ) $ 1,087.5 LIABILITIES AND EQUITY Accounts payable $ 0.2 $ 69.6 $ 38.9 $ 35.5 $ 0.0 $ 144.2 Affiliated payables 0.0 46.0 20.7 24.5 (91.2 ) 0.0 Accrued liabilities 0.0 49.5 18.9 37.9 0.0 106.3 Current maturities of long-term debt 0.0 30.2 0.0 12.4 0.0 42.6 Total current liabilities 0.2 195.3 78.5 110.3 (91.2 ) 293.1 Long-term debt 0.0 592.0 0.0 27.8 0.0 619.8 Affiliated debt 0.0 209.9 23.5 30.7 (264.1 ) 0.0 Other long-term liabilities 0.0 75.0 11.6 53.4 0.0 140.0 Total liabilities 0.2 1,072.2 113.6 222.2 (355.3 ) 1,052.9 Koppers shareholders’ equity 30.4 30.0 679.5 205.6 (915.1 ) 30.4 Noncontrolling interests 0.0 0.0 0.0 4.2 0.0 4.2 Total liabilities and equity $ 30.6 $ 1,102.2 $ 793.1 $ 432.0 $ (1,270.4 ) $ 1,087.5 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ 2.5 $ 116.8 $ 39.3 $ 60.7 $ (117.5 ) $ 101.8 Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (42.2 ) (13.5 ) (11.8 ) 0.0 (67.5 ) Repayments (loans to) from affiliates 0.0 (0.6 ) 64.2 18.1 (81.7 ) 0.0 Repayment of loan 0.0 0.0 0.0 9.5 0.0 9.5 Net cash proceeds (payments) from divestitures and asset sales 0.0 0.1 1.0 0.4 0.0 1.5 Net cash (used in) provided by investing activities 0.0 (42.7 ) 51.7 16.2 (81.7 ) (56.5 ) Cash provided by (used in) financing activities: (Repayments) borrowings of long-term debt 0.0 17.0 0.0 (9.3 ) (0.1 ) 7.6 Borrowings (repayments) of affiliated debt 0.0 (75.6 ) 9.1 (15.2 ) 81.7 0.0 Deferred financing costs 0.0 (11.0 ) 0.0 0.0 0.0 (11.0 ) Dividends paid 0.0 (3.8 ) (100.1 ) (13.7 ) 117.6 0.0 Stock repurchased (2.5 ) 0.0 0.0 0.0 0.0 (2.5 ) Net cash used in financing activities (2.5 ) (73.4 ) (91.0 ) (38.2 ) 199.2 (5.9 ) Effect of exchange rates on cash 0.0 0.0 0.0 0.1 0.0 0.1 Net increase (decrease) in cash and cash equivalents 0.0 0.7 0.0 38.8 0.0 39.5 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 $ 0.7 $ 0.0 $ 59.6 $ 0.0 $ 60.3 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2016 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ (0.1 ) $ 106.6 $ 77.0 $ 29.1 $ (93.1 ) $ 119.5 Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (30.1 ) (7.1 ) (12.7 ) 0.0 (49.9 ) Repayments (loans to) from affiliates 0.0 (6.9 ) 16.9 9.8 (19.8 ) 0.0 Net cash proceeds (payments) from divestitures and asset sales 0.0 0.0 0.9 (4.7 ) 0.0 (3.8 ) Net cash (used in) provided by investing activities 0.0 (37.0 ) 10.7 (7.6 ) (19.8 ) (53.7 ) Cash provided by (used in) financing activities: (Repayments) borrowings of long-term debt 0.0 (59.9 ) 0.1 (1.6 ) 0.0 (61.4 ) Borrowings (repayments) of affiliated debt 0.0 (7.2 ) (6.5 ) (6.1 ) 19.8 0.0 Deferred financing costs 0.0 (1.4 ) 0.0 0.0 0.0 (1.4 ) Dividends paid 0.0 (1.2 ) (82.0 ) (9.9 ) 93.1 0.0 Stock repurchased 0.1 0.0 0.0 0.0 0.0 0.1 Net cash used in financing activities 0.1 (69.7 ) (88.4 ) (17.6 ) 112.9 (62.7 ) Effect of exchange rates on cash 0.0 0.0 0.0 (4.1 ) 0.0 (4.1 ) Net increase (decrease) in cash and cash equivalents 0.0 (0.1 ) (0.7 ) (0.2 ) 0.0 (1.0 ) Cash and cash equivalents at beginning of year 0.0 0.1 0.7 21.0 0.0 21.8 Cash and cash equivalents at end of period $ 0.0 $ 0.0 $ 0.0 $ 20.8 $ 0.0 $ 20.8 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2015 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ 5.4 $ 63.0 $ 55.9 $ 60.3 $ (56.9 ) $ 127.7 Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (41.2 ) (5.3 ) (9.5 ) 0.0 (56.0 ) (Loans to) repayments from affiliates 0.0 6.3 (5.1 ) 9.2 (10.4 ) 0.0 Net cash proceeds from divestitures and asset sales 0.0 12.3 2.1 0.5 0.0 14.9 Net cash (used in) provided by investing activities 0.0 (22.6 ) (8.3 ) 0.2 (10.4 ) (41.1 ) Cash provided by (used in) financing activities: Borrowings (repayments) of long-term debt 0.0 (104.2 ) 0.1 (9.3 ) 0.0 (113.4 ) Borrowings (repayments) of affiliated debt 0.0 71.0 (6.4 ) (75.0 ) 10.4 0.0 Deferred financing costs 0.0 (1.0 ) 0.0 0.0 0.0 (1.0 ) Dividends paid (5.1 ) (6.2 ) (40.8 ) (13.5 ) 56.9 (8.7 ) Stock (repurchased) issued (0.3 ) 0.0 0.0 0.0 0.0 (0.3 ) Net cash (used in) provided by financing activities (5.4 ) (40.4 ) (47.1 ) (97.8 ) 67.3 (123.4 ) Effect of exchange rates on cash 0.0 0.1 (0.7 ) 8.1 0.0 7.5 Net (decrease) increase in cash and cash equivalents 0.0 0.1 (0.2 ) (29.2 ) 0.0 (29.3 ) Cash and cash equivalents at beginning of year 0.0 0.0 0.9 50.2 0.0 51.1 Cash and cash equivalents at end of period $ 0.0 $ 0.1 $ 0.7 $ 21.0 $ 0.0 $ 21.8

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation And Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS For the years ended December 31, 2017, 2016 and 2015 Balance at Balance Beginning Business Increase Net Currency at End of Year Acquisition to Expense Write-offs Translation of Year (Dollars in millions) 2017 Allowance for doubtful accounts $ 3.8 $ 0.0 $ 0.4 $ (1.8 ) $ 0.1 $ 2.5 Deferred tax valuation allowance $ 40.2 $ 0.0 $ 4.0 $ (0.5 ) $ 0.8 $ 44.5 2016 Allowance for doubtful accounts $ 6.5 $ 0.0 $ 0.7 $ (3.4 ) $ 0.0 $ 3.8 Deferred tax valuation allowance $ 41.9 $ 0.0 $ 0.9 $ (1.5 ) $ (1.1 ) $ 40.2 2015 Allowance for doubtful accounts $ 5.6 $ 0.0 $ 1.3 $ 0.0 $ (0.4 ) $ 6.5 Deferred tax valuation allowance $ 32.4 $ 0.0 $ 10.1 $ 0.0 $ (0.6 ) $ 41.9

Summary of Significant Accoun34

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of presentation – The consolidated financial statements include the accounts of the Company and all majority-owned subsidiaries for which the Company is deemed to exercise control over its operations. All significant intercompany transactions have been eliminated in consolidation. The Company’s investments in 20 percent to 50 percent-owned companies in which it has the ability to exercise significant influence over operating and financial policies are accounted for using the equity method of accounting. Accordingly, the Company’s share of the earnings of these companies is included in the accompanying consolidated statement of operations. As of November 2016, the Company had no investments under the equity method of accounting. Certain prior period amounts in the notes to the consolidated financial statements have been reclassified to conform to the current period’s presentation.
Use of Estimates	Use of estimates – Accounting principles generally accepted in the U.S. require management to make estimates and judgments that affect the reported amounts of assets and liabilities and the disclosure of contingencies on the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Estimates have been prepared on the basis of the most current and best available information and actual results could differ materially from these estimates.
Foreign Currency Translation	Foreign currency translation – For consolidated entities outside of the U.S. that prepare financial statements in currencies other than the U.S. dollar, results of operations and cash flows are translated at average exchange rates during the period, and assets and liabilities are translated at end-of-period exchange rates. Cumulative translation adjustments are included as a separate component of accumulated other comprehensive loss in shareholders’ equity. Foreign currency transaction gains and losses result from transactions denominated in a currency which is different than the currency used by the entity to prepare its financial statements. Foreign currency transaction losses were $2.3 million, $1.3 million and $10.4 million for the years ended December 31, 2017, 2016 and 2015, respectively.
Revenue Recognition	Revenue recognition – The Company recognizes revenue when the risks and rewards of ownership and title to the product have transferred to the customer. Revenue recognition generally occurs at the point of shipment; however in certain circumstances as shipping terms dictate, revenue is recognized at the point of destination. Shipping and handling costs are included as a component of cost of sales. The Company recognizes revenue related to the procurement of certain untreated railroad crossties upon transfer of title to the customer, which occurs upon delivery to the Company’s plant and acceptance by the customer. Payment on sales of untreated railroad crossties and wood treating services are generally due within 30 days of the invoice date. Service revenue, consisting primarily of wood treating services, is recognized at the time the service is provided. The Company’s recognition of revenue with respect to untreated crossties meets all the recognition criteria of Securities and Exchange Commission Staff Accounting Bulletin Topic 13.A.3., including transfer of title and risk of ownership, the existence of fixed purchase commitments and delivery schedules established by the customer, and the completion of all performance obligations by the Company. Revenue recognized for untreated crosstie sales for the years ended December 31, 2017, 2016 and 2015 amounted to $96.8 million, $129.2 million and $129.8 million, respectively.
Research and Development	Research and development – Research and development costs are expensed as incurred and are included in selling, general and administrative expenses. These costs totaled $9.0 million in 2017, $6.6 million in 2016 and $5.2 million in 2015.
Cash and Cash Equivalents	Cash and cash equivalents – Cash and cash equivalents include cash on hand and on deposit and investments in highly liquid investments with an original maturity of 90 days or less.
Accounts Receivable	Accounts receivable – The Company maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments. In circumstances where the Company becomes aware of a specific customer’s inability to meet its financial obligations to Koppers, a specific reserve for bad debts is recorded against amounts due. If the financial condition of the Company’s customers were to deteriorate, resulting in an inability to make payments, additional allowances may be required.
Inventories	Inventories – In the United States, CMC and RUPS inventories are valued at the lower of cost, utilizing the last-in, first-out (“LIFO”) basis, or market. PC inventories and all other inventories outside of the United States are valued at the lower of cost, utilizing the first-in, first-out (“FIFO”) basis, and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. LIFO inventories constituted approximately 52 percent and 65 percent of the FIFO inventory value at December 31, 2017 and 2016, respectively. In 2017, 2016 and 2015, we recorded inventory write-downs of $0.4 million, $0.6 million and $1.4 million, respectively, related to lower of cost and net realizable value for our subsidiaries that value inventory on the FIFO basis.
Property, Plant and Equipment	Property, plant and equipment – Property, plant and equipment are recorded at purchased cost and include improvements which significantly increase capacities or extend useful lives of existing plant and equipment. Depreciation expense is calculated by applying the straight-line method over estimated useful lives. Estimated useful lives for buildings generally range from 10 to 20 years and depreciable lives for machinery and equipment generally range from 3 to 15 years. Net gains and losses related to asset disposals are recognized in earnings in the period in which the disposal occurs. Routine repairs, replacements and maintenance are expensed as incurred. The Company periodically evaluates whether current facts and circumstances indicate that the carrying value of its depreciable long-lived assets may not be recoverable. If an asset, or logical grouping of assets, is determined to be impaired, the asset is written down to its fair value using discounted future cash flows and, if available, quoted market prices. Refer to Note 4 “Plant Closures and Discontinued Operations” for additional information.
Goodwill and Other Intangible Assets	Goodwill and other intangible assets – Goodwill and other purchased intangible assets are included in the identifiable assets of the business segment to which they have been assigned. The Company performs impairment tests annually for goodwill, and more often as circumstances require. When it is determined that impairment has occurred, an appropriate charge to earnings is recorded. The Company performed its annual impairment test in the fourth quarters of 2017 and 2016, noting no impairment. Refer to Note 14 "Goodwill and Other Identifiable Intangible Assets" for a discussion of goodwill impairment recorded during the year ended December 31, 2015. Identifiable intangible assets, other than goodwill, are recorded at cost. Identifiable intangible assets that do not have indefinite lives are amortized on a straight-line basis over their estimated useful lives.
Deferred Income Taxes	Deferred income taxes – Deferred tax assets and liabilities are recognized for future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. The effect on deferred tax assets and liabilities of a change in tax laws is recognized in earnings in the period the new laws are enacted. A valuation allowance is recorded to reduce the carrying amounts of deferred tax assets unless it is more likely than not that such assets will be realized.
Self-insured Liabilities	Self-insured liabilities – The Company is self-insured for property, casualty and workers’ compensation exposures up to various stop-loss coverage amounts. Losses are accrued based upon the Company’s estimates of the liability for the related deductibles of claims incurred. Such estimates utilize actuarial methods based on various assumptions, which include but are not limited to, the Company’s historical loss experience and projected loss development factors. In 2017 and 2016, reversals of self-insured liabilities occurred as a result of favorable loss trends related to self-insured claims. 2017 2016 (Dollars in millions) Self-insured liabilities at beginning of year $ 10.9 $ 8.0 Expense 1.9 5.1 Change in reserves recoverable from insurance (0.3 ) 2.4 Reversal of self-insured liabilities (0.4 ) (1.7 ) Cash expenditures (2.6 ) (2.9 ) Self-insured liabilities at end of year $ 9.5 $ 10.9
Derivative Financial Instruments	Derivative financial instruments – The Company uses swap contracts to manage copper price risk associated with forecasted purchases of materials used in the Company’s manufacturing processes. The Company uses forward contracts to hedge exposure to currency exchange rate changes on transactions and other commitments denominated in a foreign currency. Contracts are not held for trading or speculative purposes. The Company recognizes the fair value of the swap and forward contracts as an asset or liability at each reporting date. The Company designates certain of the swap and forward contracts as cash flow hedges and the effective portion of the gain or loss on the derivative is reported as a component of accumulated other comprehensive income (loss) until it is reclassified into earnings when the hedged transaction affects earnings. Gains and losses from hedge ineffectiveness are recognized in current earnings. For swap and forward contracts that are not designated as cash flow hedges, changes in the fair value of those contracts are recognized immediately in earnings.
Asset Retirement Obligations	Asset retirement obligations – Asset retirement obligations are initially recorded at present value and are capitalized as part of the cost of the related long-lived asset when sufficient information is available to estimate present value. The capitalized costs are subsequently charged to depreciation expense over the estimated useful life of the related long-lived asset. The present value of the obligation is determined by calculating the discounted value of expected future cash flows and accretion expense is recorded each month to ultimately increase this obligation to full value. 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 describes changes to the Company’s asset retirement obligation liabilities at December 31, 2017 and 2016: 2017 2016 (Dollars in millions) Asset retirement obligation at beginning of year $ 36.0 $ 46.5 Divestiture 0.0 (8.0 ) Accretion expense 2.4 7.1 Revision in estimated cash flows (a) 9.4 2.7 Cash expenditures (10.9 ) (11.4 ) Currency translation 0.2 (0.9 ) Balance at end of period $ 37.1 $ 36.0 (a) Revision in estimated cash flows for 2017 and 2016 includes $9.4 and $2.7 million of charges related to restructuring activities, respectively. See Note 4. “Plant Closures and Discontinued Operations” for additional information.
Litigation and Contingencies	Litigation and contingencies – Amounts associated with litigation and contingencies are accrued when management, after taking into consideration the facts and circumstances of each matter including any settlement offers, has determined that it is probable that a liability has been incurred and the amount of loss can be reasonably estimated. Legal costs for litigation are expensed as incurred with the exception of legal fees relating to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites.
Other Current Assets	Other current assets – Included in other current assets are prepaid expenses totaling $18.6 million and $17.0 million at December 31, 2017 and 2016, respectively.
Environmental Liabilities	Environmental liabilities – The Company accrues for remediation costs and penalties when the responsibility to remediate is probable and the amount of related cost is reasonably estimable. If only a range of potential liability can be estimated and no amount within the range is more probable than another, the accrual is recorded at the low end of that range. Remediation liabilities are discounted if the amount and timing of the cash disbursements are readily determinable.
Deferred Revenue from Extended Product Warranty Liabilities	Deferred revenue – The Company received an advance payment of $30.0 million in 2015 related to an amendment to a 50-year supply agreement with a customer in China. The deferred revenue associated with this amendment will be amortized over the life of the underlying contract. In addition, 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 describes changes to the Company’s deferred revenue at December 31, 2017 and 2016: 2017 2016 (Dollars in millions) Deferred revenue at beginning of year $ 27.2 $ 30.1 Revenue earned (0.7 ) (0.8 ) Currency translation 1.6 (2.1 ) Deferred revenue at end of year $ 28.1 $ 27.2
Stock-based Compensation	Stock-based compensation – The Company records compensation expense for non-vested stock options and stock units over the vesting period based on the fair value at the date of grant. No compensation cost is recognized for any stock awards that are forfeited in the event the recipient fails to meet the vesting requirements.
New Accounting Pronouncements	The Company adopted Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) No. 2016-09, “Improvements to Employee Share-Based Payment Accounting” effective January 1, 2017. This ASU makes several modifications related to the accounting for forfeitures of share-based awards, employer tax withholding on share-based compensation and the financial statement presentation of excess tax benefits or deficiencies. The Company elected to account for forfeitures when they occur. The impact of adoption was a decrease to retained earnings of $0.2 million, an increase to deferred tax assets of $0.1 million and an increase to additional paid in capital of $0.3 million. The Company adopted ASU No. 2018-02, “Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” effective October 1, 2017. ASU 2018-02 requires a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the newly enacted federal corporate income tax rate. The amount of the reclassification is the difference between the tax-effected items that are included in accumulated other comprehensive income and were recorded at the historical 35 percent corporate income tax rate and those same items that are now recorded at the newly enacted 21 percent corporate income tax rate. This difference was $3.2 million for the year ended December 31, 2017. In May 2014, the 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 are effective for annual reporting periods beginning after December 15, 2017. The Company has decided to use the modified retrospective method for transition in which the cumulative effect will be recognized at the date of adoption with no restatement of comparative periods presented. The Company has completed its analysis of significant contracts with customers across all major business units to assess the impact of the adoption of the ASUs on the Company’s financial statements and disclosures. The Company utilized a bottom-up approach to analyze the impact of the standard on its contract portfolio by reviewing its current accounting policies and practices to identify potential differences that would result from applying the requirements of the new standard to its revenue contracts. In addition, the Company identified and implemented appropriate changes to our business processes, systems and controls to support recognition and disclosure under the new standard. The implementation team has reported the findings and progress of the project to management and the Audit Committee on a frequent basis over the last year. Substantially all of the Company’s contracts with its customers are ship and invoice arrangements where revenue is recognized at the time of shipment or delivery. The Company has identified certain arrangements where revenue will be accelerated upon adoption as the related performance obligations under the contract have been satisfied and control of the goods or services have been transferred to the customer prior to shipment. After assessing the results of the completed analysis, the Company calculated the cumulative effect to the opening balance of retained earnings recognized at January 1, 2018 will be an increase of approximately $1 million, including approximately $5 million in revenue not recognized as of December 31, 2017. The impact of adopting Topic 606 is primarily related to certain services to untreated cross-ties within our RUPS segment where those specific performance obligations were fulfilled prior to shipment and historically not recognized as revenue until shipped. In August 2017, the FASB issu ed 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. ASU No. 2017-12 is effective for periods beginning after December 15, 2019, and earlier adoption is permitted. The Company will adopt this ASU effective January 1, 2018 and the impact of adoption is not expected to have a material impact on its consolidated financial statements. 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. The Company will adopt this ASU effective January 1, 2018 and does not anticipate ASU 2017-04 will impact our financial statements as there is a sufficient excess between the fair value and carrying value of our goodwill. In August 2016, the FASB 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 early adoption is permitted. The guidance requires a modified retrospective adoption. The Company is currently evaluating the impact the adoption of ASU 2016-02 will have on its consolidated financial statements.

Summary of Significant Accoun35

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Self-Insured Liabilities	Company’s historical loss experience and projected loss development factors. In 2017 and 2016, reversals of self-insured liabilities occurred as a result of favorable loss trends related to self-insured claims. 2017 2016 (Dollars in millions) Self-insured liabilities at beginning of year $ 10.9 $ 8.0 Expense 1.9 5.1 Change in reserves recoverable from insurance (0.3 ) 2.4 Reversal of self-insured liabilities (0.4 ) (1.7 ) Cash expenditures (2.6 ) (2.9 ) Self-insured liabilities at end of year $ 9.5 $ 10.9
Summary of Asset Retirement Obligation Liabilities	The following table describes changes to the Company’s asset retirement obligation liabilities at December 31, 2017 and 2016: 2017 2016 (Dollars in millions) Asset retirement obligation at beginning of year $ 36.0 $ 46.5 Divestiture 0.0 (8.0 ) Accretion expense 2.4 7.1 Revision in estimated cash flows (a) 9.4 2.7 Cash expenditures (10.9 ) (11.4 ) Currency translation 0.2 (0.9 ) Balance at end of period $ 37.1 $ 36.0 (a) Revision in estimated cash flows for 2017 and 2016 includes $9.4 and $2.7 million of charges related to restructuring activities, respectively. See Note 4. “Plant Closures and Discontinued Operations” for additional information.
Deferred Revenue from Extended Product Warranty Liabilities	The following table describes changes to the Company’s deferred revenue at December 31, 2017 and 2016: 2017 2016 (Dollars in millions) Deferred revenue at beginning of year $ 27.2 $ 30.1 Revenue earned (0.7 ) (0.8 ) Currency translation 1.6 (2.1 ) Deferred revenue at end of year $ 28.1 $ 27.2

Plant Closures and Discontinu36

Plant Closures and Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2017
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 employee Environmental remediation Asset retirement Other Total (Dollars in millions) Reserve at December 31, 2015 $ 2.0 $ 4.3 $ 21.9 $ 0.0 $ 28.2 Accrual 2.4 0.1 5.6 5.6 13.7 Costs charged against assets 0.0 0.0 0.0 (1.9 ) (1.9 ) Reversal of accrued charges (1.9 ) (0.5 ) (8.7 ) (0.1 ) (11.2 ) Cash paid (1.0 ) (2.4 ) (8.1 ) (0.2 ) (11.7 ) Currency translation (0.1 ) 0.0 (0.7 ) (0.2 ) (1.0 ) 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 Costs 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

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
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 December 31, 2017 and 2016 are as follows: December 31, 2017 December 31, 2016 Fair Value Carrying Value Fair Value Carrying Value (Dollars in millions) Financial assets: Cash and cash equivalents, including restricted cash $ 60.3 $ 60.3 $ 20.8 $ 20.8 Investments and other assets (a) 1.1 1.1 1.1 1.1 Financial liabilities: Long-term debt (including current portion) $ 706.9 $ 688.7 $ 669.6 $ 671.1 (a) Excludes equity method investments.

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Earnings (Loss) per Common Share	The following table sets forth the computation of basic and diluted earnings (loss) per common share: Year Ended December 31, 2017 2016 2015 (Dollars in millions, except share amounts, in thousands, and per share amounts) Net income (loss) attributable to Koppers $ 29.1 $ 29.3 $ (72.0 ) (Loss) income from discontinued operations (0.8 ) 0.6 (0.1 ) Income (loss) from continuing operations attributable to Koppers $ 29.9 $ 28.7 $ (71.9 ) Weighted average common shares outstanding: Basic 20,754 20,636 20,541 Effect of dilutive securities 1,246 419 0 Diluted 22,000 21,055 20,541 Earnings (loss) per common share – continuing operations: Basic earnings (loss) per common share $ 1.44 $ 1.39 $ (3.50 ) Diluted earnings (loss) per common share 1.36 1.36 (3.50 ) Other data: Antidilutive securities excluded from computation of diluted earnings per common share 156 415 668

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
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: March March March 2015 Grant Grant date price per share of stock option award $ 44.10 $ 18.11 $ 17.57 Expected dividend yield per share 0.00 % 0.00 % 3.40 % Expected life in years 5.77 5.96 5.75 Expected volatility 39.70 % 40.86 % 42.27 % Risk-free interest rate 2.13 % 1.45 % 1.73 % Grant date fair value per share of option awards $ 17.90 $ 7.41 $ 5.20
Summary of Performance Stock Units	The following table shows a summary of the performance stock units as of December 31, 2017: Performance Period Minimum Shares Target Shares Maximum Shares 2015 – 2017 0 203,953 407,906 2016 – 2018 0 260,588 521,176 2017 – 2019 0 117,010 234,020
Summary of Status and Activity of Non-Vested Stock Awards	The following table shows a summary of the status and activity of non-vested stock awards for the year ended December 31, 2017: Restricted Stock Units Performance Stock Units Total Stock Units Weighted Grant Date Fair Value per Unit Non-vested at January 1, 2017 279,807 554,388 834,195 $ 23.09 Granted 86,779 117,010 203,789 $ 55.14 Vested (128,276 ) 0 (128,276 ) $ 24.99 Forfeited (170 ) (89,847 ) (90,017 ) $ 37.80 Non-vested at December 31, 2017 238,140 581,551 819,691 $ 29.14
Summary of Status and Activity of Stock Options	The following table shows a summary of the status and activity of stock options for the year ended December 31, 2017: Options Weighted Exercise Price per Option Weighted Average Remaining Contractual Term (in years) Aggregate Value (in millions) Outstanding at December 31, 2016 935,454 $ 26.10 Granted 97,403 $ 44.10 Exercised (90,320 ) $ 29.95 Outstanding at December 31, 2017 942,537 $ 27.59 6.21 $ 22.0 Exercisable at December 31, 2017 530,762 $ 30.33 4.80 $ 10.9
Schedule of Stock-based Compensation Expense Recognized and Cash Received from Exercise of Stock Options	Stock Compensation Expense Total stock-based compensation expense recognized and cash received from the exercise of stock options for the three years ended December 31, 2017, 2016 and 2015 are as follows: Year Ended December 31, 2017 2016 2015 (Dollars in millions) Stock-based compensation expense recognized: Selling, general and administrative expenses $ 10.6 $ 8.9 $ 3.8 Less related income tax benefit 4.1 3.6 1.5 Decrease in net income attributable to Koppers $ 6.5 $ 5.3 $ 2.3 Intrinsic value of exercised stock options $ 1.3 $ 0.1 $ 0.0 Cash received from the exercise of stock options $ 2.7 $ 0.4 $ 0.0
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: March March Grant date price per share of performance award $ 44.10 $ 18.11 Expected dividend yield per share 0.00 % 0.00 % Expected volatility 43.50 % 40.86 % Risk-free interest rate 1.54 % 0.96 % Look-back period in years 2.83 2.84 Grant date fair value per share of performance award $ 64.02 $ 23.70

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
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: Year Ended December 31, 2017 2016 2015 (Dollars in millions) Revenues from external customers: Railroad and Utility Products and Services $ 512.6 $ 586.5 $ 657.0 Performance Chemicals 411.2 393.4 356.5 Carbon Materials and Chemicals 551.7 436.3 613.4 Total $ 1,475.5 $ 1,416.2 $ 1,626.9 Intersegment revenues: Performance Chemicals $ 6.7 $ 8.1 $ 8.7 Carbon Materials and Chemicals 79.6 90.2 86.7 Total $ 86.3 $ 98.3 $ 95.4 Depreciation and amortization expense: Railroad and Utility Products and Services (a) $ 11.8 $ 11.9 $ 14.2 Performance Chemicals 17.9 18.7 19.0 Carbon Materials and Chemicals (b) 20.1 22.3 25.8 Total $ 49.8 $ 52.9 $ 59.0 Operating profit (loss): Railroad and Utility Products and Services (c) $ 25.3 $ 52.5 $ 62.2 Performance Chemicals 71.4 63.5 39.0 Carbon Materials and Chemicals (d) 27.4 (23.6 ) (125.0 ) Corporate (e) (12.0 ) (6.0 ) (5.8 ) Total $ 112.1 $ 86.4 $ (29.6 ) Capital expenditures (including acquisitions): Railroad and Utility Products and Services $ 10.6 $ 11.2 $ 11.1 Performance Chemicals 15.4 7.9 5.8 Carbon Materials and Chemicals 39.7 29.5 37.6 Corporate 1.8 1.3 1.5 Total $ 67.5 $ 49.9 $ 56.0 (a) Excludes impairment charges of $1.9 million in 2015 for a wood treating facility in the United States. (b) Excludes impairment charges of $3.7, $3.5 and $12.8 million in 2017, 2016 and 2015, respectively, for CMC. (c) Includes asset retirement obligation and other restructuring costs of $1.6 million for the restructuring of two facilities in the United States in 2017. Includes asset retirement obligation and other restructuring costs of $6.9 million for the restructuring of three facilities in the United States in 2016. Includes gain on sale of the Company’s North American utility pole business of $3.2 million and restructuring costs of $5.7 million for a wood treating facility in the United States in 2015. (d) Includes plant closure costs of $14.6, $13.2 and $36.5 million in 2017, 2016 and 2015, respectively, for CMC. In the fourth quarter of 2015, the Company also recorded goodwill impairment charges of $67.2 million related to this business unit. (e) Operating loss for Corporate includes general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc., pension settlement losses, foreign exchange revaluation related to intercompany loans in connection with a legal reorganization of the Company and acquisition and acquisition-related integration costs.
Summary of Tangible and Intangible Assets by Segments	The following table sets forth tangible and intangible assets allocated to each of the Company’s segments as of the dates indicated: December 31, 2017 2016 (Dollars in millions) Segment assets: Railroad and Utility Products and Services $ 249.7 $ 264.2 Performance Chemicals 494.0 442.9 Carbon Materials and Chemicals 414.2 333.0 Segment assets 1,157.9 1,040.1 Cash and cash equivalents 0.7 0.0 Income tax receivable 1.7 3.8 Deferred taxes 29.4 32.5 Property, plant and equipment, net 5.2 4.9 Deferred charges 0.2 0.7 Other 5.1 5.5 Total $ 1,200.2 $ 1,087.5 Goodwill: Railroad and Utility Products and Services $ 10.5 $ 9.9 Performance Chemicals 177.7 176.5 Total $ 188.2 $ 186.4
Schedule of Revenues and Long-Lived Assets by Geographic Area	Revenues and Long-lived Assets by Geographic Area Year Revenue Long-lived assets (Dollars in millions) United States 2017 $ 852.2 $ 479.5 2016 929.3 446.6 2015 991.2 460.3 Australasia 2017 312.8 131.4 2016 228.4 124.3 2015 280.9 132.9 Europe 2017 173.1 44.8 2016 140.2 31.9 2015 144.0 32.9 Other countries 2017 137.4 19.4 2016 118.3 19.5 2015 210.8 18.3 Total 2017 $ 1,475.5 $ 675.1 2016 $ 1,416.2 $ 622.3 2015 $ 1,626.9 $ 644.5
Schedule of Segment Revenues for Significant Product Lines	Segment Revenues for Significant Product Lines Year Ended December 31, 2017 2016 2015 (Dollars in millions) Railroad and Utility Products and Services: Railroad crossties $ 326.7 $ 374.0 $ 422.0 Utility poles 36.5 34.5 52.4 Creosote 45.3 49.6 45.7 Rail joints 28.2 24.4 28.1 Railroad infrastructure services 34.8 43.4 42.7 Other products 41.1 60.6 66.1 512.6 586.5 657.0 Performance Chemicals: Wood preservative products 383.8 365.5 318.6 Other products 27.4 27.9 37.9 411.2 393.4 356.5 Carbon Materials and Chemicals: Carbon pitch 223.3 191.0 283.4 Phthalic anhydride 93.5 75.6 65.1 Creosote and carbon black feedstock 89.6 71.3 119.6 Other products 145.3 98.4 145.3 551.7 436.3 613.4 Total $ 1,475.5 $ 1,416.2 $ 1,626.9

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Summary of Income Tax Provision	Components of the Company’s income tax provision from continuing operations are as follows: Year Ended December 31, 2017 2016 2015 (Dollars in millions) Current: Federal $ 11.1 $ (1.9 ) $ (4.2 ) State 0.6 1.3 0.2 Foreign 15.7 13.3 16.0 Total current tax provision 27.4 12.7 12.0 Deferred: Federal 2.6 (1.6 ) (19.2 ) State (1.2 ) 0.5 3.0 Foreign 0.2 (0.2 ) 0.0 Total deferred tax provision (benefit) 1.6 (1.3 ) (16.2 ) Total income tax provision (benefit) $ 29.0 $ 11.4 $ (4.2 )
Summary of Income Taxes Reconciled with Federal Statutory Rate	The provision for income taxes is reconciled with the federal statutory rate as follows: Year Ended December 31, 2017 2016 2015 Federal income tax rate 35.0 % 35.0 % 35.0 % State income taxes, net of federal tax benefit (1.6 ) (0.8 ) 2.3 Foreign earnings taxed at different rates (21.6 ) (10.1 ) (8.3 ) Transition tax from Tax Act 21.7 0.0 0.0 Deferred tax adjustments from Tax Act 12.3 0.0 0.0 Change in tax contingency reserves 2.2 6.5 1.5 Valuation allowance adjustments 0.9 (1.9 ) (13.0 ) Domestic production activities deduction 0.0 0.0 (0.6 ) Goodwill impairment 0.0 0.0 (10.9 ) Deferred tax adjustments 0.0 (0.2 ) 0.4 Other (0.8 ) 1.1 (1.1 ) 48.1 % 29.6 % 5.3 %
Summary of Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax assets and liabilities are as follows: December 31, 2017 2016 (Dollars in millions) Deferred tax assets: Federal and state tax loss carryforwards (expiring from 2018-2036) $ 21.2 $ 11.3 Tax credits 15.0 15.4 Reserves, including insurance, environmental and deferred revenue 14.3 22.3 Asset retirement obligations 11.9 12.0 Pension and other postretirement benefits obligations 10.8 19.2 Foreign tax loss carryforwards (expiring beginning in 2018) 9.3 10.1 Accrued employee compensation 6.3 8.9 Book/tax inventory accounting differences 1.5 3.5 Other 6.1 6.6 Valuation allowance (44.5 ) (40.2 ) Total deferred tax assets 51.9 69.1 Deferred tax liabilities: Tax over book depreciation and amortization 33.2 42.7 Gain on derivative contracts 7.0 4.2 Other 0.7 1.4 Total deferred tax liabilities 40.9 48.3 Net deferred tax assets $ 11.0 $ 20.8
Summary of Valuation Allowances Recorded to Offset Deferred Tax Assets	A valuation allowance is necessary when it is more likely than not that a deferred tax asset will not be realized. Certain deferred tax assets reflected above are not expected to be realized and a valuation allowance has been provided for them. Valuation allowances are recorded to offset the following deferred tax assets: December 31, 2017 2016 State temporary differences, net operating losses and tax credits $ 18.7 $ 13.2 Federal foreign tax credits 13.8 14.3 Foreign temporary differences, net operating losses and capital losses 12.0 12.7 Total valuation allowances $ 44.5 $ 40.2
Summary of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: December 31, 2017 2016 2015 (Dollars in millions) Balance at beginning of year $ 9.7 $ 7.7 $ 7.2 Additions based on tax provisions related to the current year 0.1 0.9 1.4 Additions for tax provisions of prior years 2.7 1.5 0.0 Reductions of tax provisions of prior years (3.4 ) 0.0 (0.7 ) Reductions as a result of a lapse of the applicable statute of limitations (0.4 ) (0.4 ) (0.2 ) Balance at end of year $ 8.7 $ 9.7 $ 7.7

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Components of Inventories	Inventories as of December 31, 2017 and 2016 were as follows: December 31, 2017 2016 (Dollars in millions) Raw materials $ 173.6 $ 157.7 Work in process 11.2 14.2 Finished goods 98.4 103.6 283.2 275.5 Less revaluation to LIFO 46.3 46.8 Net $ 236.9 $ 228.7

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Property, Plant and Equipment	Property, plant and equipment as of December 31, 2017 and 2016 were as follows: December 31, 2017 2016 (Dollars in millions) Land $ 17.6 $ 17.0 Buildings 63.4 58.2 Machinery and equipment 756.6 716.0 $ 837.6 $ 791.2 Less accumulated depreciation 509.6 510.4 Net $ 328.0 $ 280.8

Goodwill and Other Identifiab44

Goodwill and Other Identifiable Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Changes in Carrying Amount of Goodwill	The change in the carrying amount of goodwill attributable to each business segment for the years ended December 31, 2017 and December 31, 2016 was as follows: Railroad and Utility Products and Services Performance Chemicals Total (Dollars in millions) Balance at December 31, 2015 $ 9.9 $ 176.7 $ 186.6 Currency translation 0.0 (0.2 ) (0.2 ) Balance at December 31, 2016 $ 9.9 $ 176.5 $ 186.4 Currency translation 0.6 1.2 1.8 Balance at December 31, 2017 $ 10.5 $ 177.7 $ 188.2
Schedule of Identifiable Intangible Assets	The Company’s identifiable intangible assets with finite lives are being amortized over their estimated useful lives and are summarized below: December 31, 2017 2016 Estimated life in years Weighted average remaining life in years Gross Carrying Amount Accumulated Amortization Net Gross Carrying Amount Accumulated Amortization Net (Dollars in millions) Customer contracts 9 to 18 12.2 $ 154.7 $ 43.9 $ 110.8 $ 152.5 $ 33.6 $ 118.9 Technology 4 to 12 4.0 26.8 12.5 14.3 26.7 8.8 17.9 Trademarks 4 to 7 4.0 6.5 2.7 3.8 6.1 1.9 4.2 Supply contracts 10 2.2 2.5 2.0 0.5 2.2 1.5 0.7 Non-compete agreements 12 6.8 1.4 1.2 0.2 1.3 1.1 0.2 Favorable lease agreements 3 0.0 0.7 0.7 0.0 0.6 0.6 0.0 Total 11.1 $ 192.6 $ 63.0 $ 129.6 $ 189.4 $ 47.5 $ 141.9
Schedule of Future Amortization Expense	Estimated amortization expense for the next five years is summarized below: Estimated annual amortization (Dollars in millions) 2018 $ 14.5 2019 14.5 2020 14.2 2021 12.3 2022 9.6

Pensions and Post-Retirement 45

Pensions and Post-Retirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans	Net periodic pension costs for 2017, 2016 and 2015 were as follows: Year Ended December 31, Pension Benefits Other Benefits 2017 2016 2015 2017 2016 2015 (Dollars in millions) Service cost $ 2.0 $ 1.7 $ 2.0 $ 0.1 $ 0.1 $ 0.1 Interest cost 9.0 11.0 10.9 0.4 0.4 0.4 Expected return on plan assets (9.6 ) (10.5 ) (12.0 ) 0.0 0.0 0.0 Amortization of prior service cost 0.0 0.0 (0.3 ) 0.0 0.0 (0.1 ) Amortization of net loss 1.9 2.2 6.6 (0.2 ) (0.4 ) (0.3 ) Settlements and curtailments 10.0 4.4 (0.8 ) 0.0 0.0 0.0 Net periodic benefit cost $ 13.3 $ 8.8 $ 6.4 $ 0.3 $ 0.1 $ 0.1
Schedule of Change in Funded Status of Pension and Post-Retirement Plans	The change in the funded status of the pension and postretirement plans as of December 31, 2017 and December 31, 2016 is as follows: December 31, Pension Benefits Other Benefits 2017 2016 2017 2016 (Dollars in millions) Change in benefit obligation: Benefit obligation at beginning of year $ 243.6 $ 257.5 $ 10.0 $ 9.4 Service cost 2.0 1.7 0.1 0.1 Interest cost 9.0 11.0 0.4 0.4 Actuarial losses 7.3 10.7 1.5 1.0 Settlements (36.9 ) (13.9 ) 0.0 0.0 Currency translation 5.5 (9.9 ) 0.0 0.0 Benefits paid (11.4 ) (13.5 ) (0.9 ) (0.9 ) Benefit obligation at end of year 219.1 243.6 11.1 10.0 Change in plan assets: Fair value of plan assets at beginning of year 200.9 212.4 0.0 0.0 Actual return on plan assets 19.5 20.8 0.0 0.0 Employer contribution 11.2 4.5 0.9 0.9 Settlements (36.9 ) (13.9 ) 0.0 0.0 Currency translation 5.5 (9.4 ) 0.0 0.0 Benefits paid (11.4 ) (13.5 ) (0.9 ) (0.9 ) Fair value of plan assets at end of year 188.8 200.9 0.0 0.0 Funded status of the plan $ (30.3 ) $ (42.7 ) $ (11.1 ) $ (10.0 ) Amounts recognized in the balance sheet consist of: Noncurrent assets $ 7.0 $ 0.8 $ 0.0 $ 0.0 Current liabilities 1.1 1.1 1.0 0.8 Noncurrent liabilities 36.2 42.4 10.1 9.2 Pension plans with projected benefit obligations in excess of plan assets: Benefit obligation $ 159.9 $ 238.7 Fair value of plan assets 122.6 195.3 Pension plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligation $ 159.6 $ 238.5 Fair value of plan assets 122.6 195.3
Schedule of Projected Benefit Payments	Benefit payments for pension benefits, which are primarily funded by the pension plan assets, and other benefits, which are funded by general corporate assets and reflecting future expected service as appropriate, are expected to be paid as follows: Pension Benefits Other Benefits (Dollars in millions) 2018 $ 11.1 $ 1.0 2019 11.0 1.0 2020 11.3 0.9 2021 11.5 0.8 2022 11.7 0.7 Next five years 64.0 3.2
Schedule of Weighted-Average Assumptions	Weighted-Average Assumptions as of December 31 December 31, Pension Benefits Other Benefits 2017 2016 2017 2016 Discount rate 3.51 % 4.09 % 3.88 % 4.53 % Expected return on plan assets 4.62 5.10 Rate of compensation increase 3.50 3.50 Initial medical trend rate 6.10 6.30
Schedule of Weighted Average Asset Allocation for Company's Pension Plans	The weighted average asset allocation for the Company’s pension plans at December 31 by asset category is as follows: December 31, 2017 2016 Debt securities 64 % 71 % Equity securities 30 24 Other 6 5 100 % 100 %
Schedule of Pension Plan Assets at Fair Value	The following table sets forth by level, the Company’s pension plan assets at fair value, within the fair value hierarchy, as of December 31, 2017 and December 31, 2016: As of December 31, 2017 Quoted prices in active Significant Significant markets for observable unobservable identical assets inputs inputs (Level 1) (Level 2) (Level 3) Total (Dollars in millions) U.S. equity securities $ 18.6 $ 12.7 $ 0.0 $ 31.3 International equity securities 15.0 10.2 0.0 25.2 U.S. debt securities 21.4 53.0 2.5 76.9 International debt securities 7.5 34.8 1.0 43.3 Real estate and other investments 0.5 0.8 8.3 9.6 Cash and cash equivalents 0.0 2.5 0.0 2.5 $ 63.0 $ 114.0 $ 11.8 $ 188.8 As of December 31, 2016 Quoted prices in active Significant Significant markets for observable unobservable identical assets inputs inputs (Level 1) (Level 2) (Level 3) Total (Dollars in millions) U.S. equity securities $ 12.3 $ 13.2 $ 0.0 $ 25.5 International equity securities 12.6 10.9 0.0 23.5 U.S. debt securities 29.7 75.2 3.2 108.1 International debt securities 8.3 24.3 1.1 33.7 Real estate and other investments 0.0 0.5 5.7 6.2 Cash and cash equivalents 0.0 3.9 0.0 3.9 $ 62.9 $ 128.0 $ 10.0 $ 200.9
Summary of Changes in Fair Value of Level 3 Pension Plan Assets	The table below sets forth a summary of changes in the fair value of the Level 3 pension plans’ assets for the year ended December 31, 2017: As of December 31, 2017 Other Investments Debt Securities (Dollars in millions) Balance at beginning of year $ 5.7 $ 4.3 Purchases, sales, issuances and settlements 1.9 (1.4 ) Realized and unrealized gains 0.7 0.6 Balance at the end of year $ 8.3 $ 3.5 The amount of total gains during the period attributable to the change in unrealized gains relating to Level 3 net assets still held at the reporting date $ 0.2 $ 0.1
Schedule of Health Care Cost Trend Rates	A one-percentage-point change in the assumed health care cost trend rate would have the following effects: 1% Increase 1% Decrease (Dollars in millions) Increase (decrease) from change in health care cost trend rates: Postretirement benefit expense $ 0.0 $ 0.0 Postretirement benefit liability 0.2 (0.1 )

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Long-Term Debt Instruments	Debt as of December 31, 2017 and 2016 was as follows: December 31, Weighted Average Interest Rate Maturity 2017 2016 Revolving Credit Facility 4.01 % 2022 $ 155.0 $ 100.1 Term Loan 0.0 232.5 Construction and other loans 4.80 % 2020 33.7 40.4 Senior Notes due 2025 6.00 % 2025 500.0 0.0 Senior Notes due 2019 0.0 298.1 Total debt 688.7 671.1 Less short-term debt and current maturities of long-term debt 11.4 42.6 Less unamortized debt issuance costs 11.7 8.7 Long-term debt $ 665.6 $ 619.8
Schedule of Debt Maturities	At December 31, 2017 the aggregate debt maturities for the next five years are as follows: (Dollars in millions) 2018 $ 11.4 2019 3.0 2020 19.3 2021 0.0 2022 155.0 Thereafter 500.0 Total debt $ 688.7

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Future Minimum Commitments for Operating Leases	Future minimum commitments for operating leases having non-cancelable lease terms in excess of one year are as follows: (Dollars in millions) 2018 $ 43.7 2019 25.3 2020 20.6 2021 16.4 2022 15.2 Thereafter 50.2 Total $ 171.4

Derivative Financial Instrume48

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Schedule of Outstanding Copper Swap Contracts	As of December 31, 2017 and December 31, 2016, the Company had outstanding copper swap contracts of the following amounts: Units Outstanding (in Pounds) Net Fair Value - Asset (Liability) December 31, December 31, 2017 2016 2017 2016 (Amounts in millions) Cash flow hedges 37.8 42.6 $ 25.5 $ 10.6 Not designated as hedges 11.3 6.5 4.5 1.0 Total 49.1 49.1 $ 30.0 $ 11.6
Schedule of Fair Value of Outstanding Copper Swap Contracts Recorded in Balance Sheet	As of December 31, 2017 and December 31, 2016, the fair value of the outstanding copper swap contracts is recorded in the balance sheet as follows: December 31, 2017 2016 (Dollars in millions) Other current assets $ 21.8 $ 12.5 Other assets 8.2 0.0 Accrued liabilities 0.0 (0.9 ) Net asset on balance sheet $ 30.0 $ 11.6 Accumulated other comprehensive gain, net of tax $ 15.8 $ 6.9
Summary of Amount Recognized in Earnings Related to Copper Swap Contracts	See the Consolidated Statement of Comprehensive Income and Consolidated Statement of Shareholders’ Equity for amounts recorded in other comprehensive income and for amounts reclassified from accumulated other comprehensive income into net income for the periods specified below. For the years ended December 31, 2017 and 2016, the following amounts were recognized in earnings related to copper swap contracts: Year Ended December 31, 2017 2016 (Dollars in millions) Gain (loss) from ineffectiveness of cash flow hedges $ 5.6 $ (0.4 ) Gain from contracts not designated as hedges 3.5 1.7 Net $ 9.1 $ 1.3
Summary of Net Currency Units Outstanding	As of December 31, 2017 and 2016, the net currency units outstanding were: December 31, 2017 2016 (In millions) British Pounds GBP 7.0 GBP 7.3 New Zealand Dollars NZD 15.5 NZD 15.5 United States Dollars USD 12.5 USD 24.7 Canadian Dollars CAD 2.5 CAD 0.3

Common Stock and Senior Conve49

Common Stock and Senior Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2017
Text Block [Abstract]
Schedule of Changes in Senior Convertible Preferred Stock, Common Stock and Treasury Stock	Changes in senior convertible preferred stock, common stock and treasury stock for the three years ended December 31, 2017 are as follows: December 31, 2017 2016 2015 (Shares in thousands) Senior Convertible Preferred Stock: Balance at beginning and end of year 0 0 0 Common Stock: Balance at beginning of year 22,141 22,016 21,938 Issued for employee stock plans 243 125 78 Balance at end of year 22,384 22,141 22,016 Treasury Stock: Balance at beginning of year (1,476 ) (1,459 ) (1,443 ) Shares repurchased (130 ) (17 ) (16 ) Balance at end of year (1,606 ) (1,476 ) (1,459 )

Commitments and Contingent Li50

Commitments and Contingent Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
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 $5.1 million and $5.2 million are classified as current liabilities at December 31, 2017 and 2016 Year Ended December 31, 2017 2016 (Dollars in millions) Balance at beginning of year $ 12.9 $ 19.8 Expense 3.2 1.5 Reversal of reserves (0.7 ) (1.0 ) Cash expenditures (1.8 ) (6.3 ) Divestitures 0.0 (0.3 ) Currency translation 0.3 (0.8 ) Balance at end of period $ 13.9 $ 12.9

Selected Quarterly Financial 51

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Data	The following is a summary of the quarterly results of operations for the years ended December 31, 2017 and 2016: Year Ended December 31, 2017 1 st 2 nd 3 rd 4 th Fiscal Year (Dollars in millions, except per share amounts) Statement of operations data: Net sales $ 346.6 $ 378.0 $ 384.8 $ 366.1 $ 1,475.5 Operating profit 27.6 37.6 34.7 12.2 112.1 Income (loss) from continuing operations (a) 4.7 20.9 20.0 (14.3 ) 31.3 Net income (loss) (a) 4.6 19.8 19.9 (13.8 ) 30.5 Net income (loss) attributable to Koppers (a) 4.4 19.7 19.8 (14.8 ) 29.1 Common stock data: Earnings (loss) per common share attributable to Koppers common shareholders: (a)(b) Basic – Continuing operations $ 0.21 $ 1.00 $ 0.96 $ (0.73 ) $ 1.44 Discontinued operations 0.00 (0.06 ) 0.00 0.02 (0.04 ) Earnings (loss) per basic common share $ 0.21 $ 0.94 $ 0.96 $ (0.71 ) $ 1.40 Diluted – Continuing operations $ 0.20 $ 0.95 $ 0.91 $ (0.73 ) $ 1.36 Discontinued operations 0.00 (0.05 ) 0.00 0.02 (0.04 ) Earnings (loss) per diluted common share $ 0.20 $ 0.90 $ 0.91 $ (0.71 ) $ 1.32 Price range of common stock: High $ 45.85 $ 44.80 $ 46.55 $ 51.80 $ 51.80 Low 39.10 33.90 35.17 45.75 33.90 Year Ended December 31, 2016 1 st 2 nd 3 rd 4 th Fiscal Year (Dollars in millions, except per share amounts) Statement of operations data: Net sales $ 346.8 $ 385.1 $ 371.1 $ 313.2 $ 1,416.20 Operating profit 7.8 32.0 27.7 18.9 86.4 Income (loss) from continuing operations (2.4 ) 11.3 12.0 6.2 27.1 Net income (loss) (1.8 ) 11.3 11.9 6.3 27.7 Net income (loss) attributable to Koppers (1.3 ) 12.1 12.1 6.4 29.3 Common stock data: Earnings (loss) per common share attributable to Koppers common shareholders: (b) Basic – Continuing operations $ (0.09 ) $ 0.58 $ 0.59 $ 0.31 $ 1.39 Discontinued operations 0.03 0.00 0.00 0.00 0.03 Earnings (loss) per basic common share $ (0.06 ) $ 0.58 $ 0.59 $ 0.31 $ 1.42 Diluted – Continuing operations $ (0.09 ) $ 0.57 $ 0.58 $ 0.30 $ 1.36 Discontinued operations 0.03 0.00 0.00 0.00 0.03 Earnings (loss) per diluted common share $ (0.06 ) $ 0.57 $ 0.58 $ 0.30 $ 1.39 Price range of common stock: High $ 23.43 $ 31.35 $ 33.71 $ 42.70 $ 42.70 Low 13.58 21.38 28.54 31.28 13.58 (a) Income tax expense for the fourth quarter of 2017 was increased by $20.5 million due to the impact of the Tax Cuts and Jobs Act which was signed into law on December 22, 2017. (b) The cumulative sum of quarterly basic and diluted net income per share amounts may not equal total basic and diluted net income per share amounts for the year due to differences in weighted average and equivalent shares outstanding for each of the periods presented.

Subsidiary Guarantor Informat52

Subsidiary Guarantor Information for Koppers Inc. 2025 Notes and Shelf Registration (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Condensed Consolidating Statement of Comprehensive Income (Loss)	Condensed Consolidating Statement of Comprehensive Income (Loss) For the Year Ended December 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 590.6 $ 344.9 $ 623.3 $ (83.3 ) $ 1,475.5 Cost of sales including depreciation and amortization 0.0 570.9 235.0 496.3 (82.1 ) 1,220.1 Loss on pension settlement 0.0 10.0 0.0 0.0 0.0 10.0 Selling, general and administrative 1.9 47.7 43.3 40.4 0.0 133.3 Operating (loss) profit (1.9 ) (38.0 ) 66.6 86.6 (1.2 ) 112.1 Other income (loss) 0.0 0.5 2.4 2.3 (1.2 ) 4.0 Equity income of subsidiaries 30.3 103.8 64.7 0.0 (198.8 ) 0.0 Interest (income) expense 0.0 39.0 0.0 4.7 (1.2 ) 42.5 Loss on extinguishment 0.0 13.3 0.0 0.0 0.0 13.3 Income taxes (0.7 ) (16.4 ) 30.0 16.2 (0.1 ) 29.0 Income from continuing operations 29.1 30.4 103.7 68.0 (199.9 ) 31.3 Discontinued operations 0.0 0.0 0.0 (0.8 ) 0.0 (0.8 ) Noncontrolling interests 0.0 0.0 0.0 1.4 0.0 1.4 Net income attributable to Koppers $ 29.1 $ 30.4 $ 103.7 $ 65.8 $ (199.9 ) $ 29.1 Comprehensive income (loss) attributable to Koppers $ 60.7 $ 61.8 $ 132.8 $ 89.2 $ (283.8 ) $ 60.7 Condensed Consolidating Statement of Comprehensive (Loss) Income For the Year Ended December 31, 2016 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 660.7 $ 350.6 $ 504.7 $ (99.8 ) $ 1,416.2 Cost of sales including depreciation and amortization 0.0 637.4 252.3 412.4 (101.2 ) 1,200.9 Gain on sale of business 0.0 0.0 0.0 (2.1 ) 0.0 (2.1 ) Loss on pension settlement 0.0 4.4 0.0 0.0 0.0 4.4 Selling, general and administrative 1.9 43.3 38.2 43.2 0.0 126.6 Operating (loss) profit (1.9 ) (24.4 ) 60.1 51.2 1.4 86.4 Other income (loss) 0.0 0.3 4.1 0.3 (1.8 ) 2.9 Equity income of subsidiaries 30.6 79.1 35.9 0.0 (145.6 ) 0.0 Interest (income) expense 0.0 47.6 0.0 5.0 (1.8 ) 50.8 Income taxes (0.6 ) (23.2 ) 22.2 13.0 0.0 11.4 Income from continuing operations 29.3 30.6 77.9 33.5 (144.2 ) 27.1 Discontinued operations 0.0 0.0 0.0 0.6 0.0 0.6 Noncontrolling interests 0.0 0.0 0.0 (1.6 ) 0.0 (1.6 ) Net income attributable to Koppers $ 29.3 $ 30.6 $ 77.9 $ 35.7 $ (144.2 ) $ 29.3 Comprehensive income (loss) attributable to Koppers $ 40.5 $ 41.3 $ 85.0 $ 29.6 $ (155.9 ) $ 40.5 Condensed Consolidating Statement of Comprehensive (Loss) Income For the Year Ended December 31, 2015 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 791.1 $ 335.6 $ 600.9 $ (100.7 ) $ 1,626.9 Cost of sales including depreciation and amortization 0.0 771.7 233.2 562.4 (99.4 ) 1,467.9 Gain on sale of business 0.0 (3.2 ) 0.0 0.0 0.0 (3.2 ) Goodwill impairment 0.0 43.1 24.1 0.0 0.0 67.2 Selling, general and administrative 1.9 41.3 37.8 43.6 0.0 124.6 Operating (loss) profit (1.9 ) (61.8 ) 40.5 (5.1 ) (1.3 ) (29.6 ) Other income (loss) 0.0 0.5 4.1 (2.4 ) (2.0 ) 0.2 Equity income of subsidiaries (70.8 ) 0.9 (27.9 ) 0.0 97.8 0.0 Interest expense 0.0 45.8 0.0 6.9 (2.0 ) 50.7 Income taxes (0.7 ) (35.4 ) 15.8 16.4 (0.3 ) (4.2 ) (Loss) income from continuing operations (72.0 ) (70.8 ) 0.9 (30.8 ) 96.8 (75.9 ) Discontinued operations 0.0 0.0 0.0 (0.1 ) 0.0 (0.1 ) Noncontrolling interests 0.0 0.0 0.0 (4.0 ) 0.0 (4.0 ) Net income attributable to Koppers $ (72.0 ) $ (70.8 ) $ 0.9 $ (26.9 ) $ 96.8 $ (72.0 ) Comprehensive income (loss) attributable to Koppers $ (91.5 ) $ (90.3 ) $ (18.1 ) $ (41.8 ) $ 150.2 $ (91.5 )
Condensed Consolidating Balance Sheet	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 Balance Sheet December 31, 2016 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) ASSETS Cash and cash equivalents $ 0.0 $ 0.0 $ 0.0 $ 20.8 $ 0.0 $ 20.8 Receivables, net 0.0 50.8 25.4 64.4 0.0 140.6 Affiliated receivables 0.7 34.8 32.2 15.4 (83.1 ) 0.0 Inventories, net 0.0 106.6 23.9 99.0 (0.8 ) 228.7 Other current assets 0.0 5.1 13.4 29.2 0.3 48.0 Total current assets 0.7 197.3 94.9 228.8 (83.6 ) 438.1 Equity investments 29.9 697.4 195.4 0.0 (922.7 ) 0.0 Property, plant and equipment, net 0.0 126.7 39.6 114.5 0.0 280.8 Goodwill 0.0 0.8 153.1 32.5 0.0 186.4 Intangible assets, net 0.0 7.9 107.1 26.9 0.0 141.9 Deferred tax assets 0.0 29.7 (8.4 ) 5.8 0.0 27.1 Affiliated loan receivables 0.0 36.9 205.3 21.9 (264.1 ) 0.0 Other assets 0.0 5.5 6.1 1.6 0.0 13.2 Total assets $ 30.6 $ 1,102.2 $ 793.1 $ 432.0 $ (1,270.4 ) $ 1,087.5 LIABILITIES AND EQUITY Accounts payable $ 0.2 $ 69.6 $ 38.9 $ 35.5 $ 0.0 $ 144.2 Affiliated payables 0.0 46.0 20.7 24.5 (91.2 ) 0.0 Accrued liabilities 0.0 49.5 18.9 37.9 0.0 106.3 Current maturities of long-term debt 0.0 30.2 0.0 12.4 0.0 42.6 Total current liabilities 0.2 195.3 78.5 110.3 (91.2 ) 293.1 Long-term debt 0.0 592.0 0.0 27.8 0.0 619.8 Affiliated debt 0.0 209.9 23.5 30.7 (264.1 ) 0.0 Other long-term liabilities 0.0 75.0 11.6 53.4 0.0 140.0 Total liabilities 0.2 1,072.2 113.6 222.2 (355.3 ) 1,052.9 Koppers shareholders’ equity 30.4 30.0 679.5 205.6 (915.1 ) 30.4 Noncontrolling interests 0.0 0.0 0.0 4.2 0.0 4.2 Total liabilities and equity $ 30.6 $ 1,102.2 $ 793.1 $ 432.0 $ (1,270.4 ) $ 1,087.5
Condensed Consolidating Statement of Cash Flows	Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ 2.5 $ 116.8 $ 39.3 $ 60.7 $ (117.5 ) $ 101.8 Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (42.2 ) (13.5 ) (11.8 ) 0.0 (67.5 ) Repayments (loans to) from affiliates 0.0 (0.6 ) 64.2 18.1 (81.7 ) 0.0 Repayment of loan 0.0 0.0 0.0 9.5 0.0 9.5 Net cash proceeds (payments) from divestitures and asset sales 0.0 0.1 1.0 0.4 0.0 1.5 Net cash (used in) provided by investing activities 0.0 (42.7 ) 51.7 16.2 (81.7 ) (56.5 ) Cash provided by (used in) financing activities: (Repayments) borrowings of long-term debt 0.0 17.0 0.0 (9.3 ) (0.1 ) 7.6 Borrowings (repayments) of affiliated debt 0.0 (75.6 ) 9.1 (15.2 ) 81.7 0.0 Deferred financing costs 0.0 (11.0 ) 0.0 0.0 0.0 (11.0 ) Dividends paid 0.0 (3.8 ) (100.1 ) (13.7 ) 117.6 0.0 Stock repurchased (2.5 ) 0.0 0.0 0.0 0.0 (2.5 ) Net cash used in financing activities (2.5 ) (73.4 ) (91.0 ) (38.2 ) 199.2 (5.9 ) Effect of exchange rates on cash 0.0 0.0 0.0 0.1 0.0 0.1 Net increase (decrease) in cash and cash equivalents 0.0 0.7 0.0 38.8 0.0 39.5 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 $ 0.7 $ 0.0 $ 59.6 $ 0.0 $ 60.3 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2016 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ (0.1 ) $ 106.6 $ 77.0 $ 29.1 $ (93.1 ) $ 119.5 Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (30.1 ) (7.1 ) (12.7 ) 0.0 (49.9 ) Repayments (loans to) from affiliates 0.0 (6.9 ) 16.9 9.8 (19.8 ) 0.0 Net cash proceeds (payments) from divestitures and asset sales 0.0 0.0 0.9 (4.7 ) 0.0 (3.8 ) Net cash (used in) provided by investing activities 0.0 (37.0 ) 10.7 (7.6 ) (19.8 ) (53.7 ) Cash provided by (used in) financing activities: (Repayments) borrowings of long-term debt 0.0 (59.9 ) 0.1 (1.6 ) 0.0 (61.4 ) Borrowings (repayments) of affiliated debt 0.0 (7.2 ) (6.5 ) (6.1 ) 19.8 0.0 Deferred financing costs 0.0 (1.4 ) 0.0 0.0 0.0 (1.4 ) Dividends paid 0.0 (1.2 ) (82.0 ) (9.9 ) 93.1 0.0 Stock repurchased 0.1 0.0 0.0 0.0 0.0 0.1 Net cash used in financing activities 0.1 (69.7 ) (88.4 ) (17.6 ) 112.9 (62.7 ) Effect of exchange rates on cash 0.0 0.0 0.0 (4.1 ) 0.0 (4.1 ) Net increase (decrease) in cash and cash equivalents 0.0 (0.1 ) (0.7 ) (0.2 ) 0.0 (1.0 ) Cash and cash equivalents at beginning of year 0.0 0.1 0.7 21.0 0.0 21.8 Cash and cash equivalents at end of period $ 0.0 $ 0.0 $ 0.0 $ 20.8 $ 0.0 $ 20.8 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2015 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ 5.4 $ 63.0 $ 55.9 $ 60.3 $ (56.9 ) $ 127.7 Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (41.2 ) (5.3 ) (9.5 ) 0.0 (56.0 ) (Loans to) repayments from affiliates 0.0 6.3 (5.1 ) 9.2 (10.4 ) 0.0 Net cash proceeds from divestitures and asset sales 0.0 12.3 2.1 0.5 0.0 14.9 Net cash (used in) provided by investing activities 0.0 (22.6 ) (8.3 ) 0.2 (10.4 ) (41.1 ) Cash provided by (used in) financing activities: Borrowings (repayments) of long-term debt 0.0 (104.2 ) 0.1 (9.3 ) 0.0 (113.4 ) Borrowings (repayments) of affiliated debt 0.0 71.0 (6.4 ) (75.0 ) 10.4 0.0 Deferred financing costs 0.0 (1.0 ) 0.0 0.0 0.0 (1.0 ) Dividends paid (5.1 ) (6.2 ) (40.8 ) (13.5 ) 56.9 (8.7 ) Stock (repurchased) issued (0.3 ) 0.0 0.0 0.0 0.0 (0.3 ) Net cash (used in) provided by financing activities (5.4 ) (40.4 ) (47.1 ) (97.8 ) 67.3 (123.4 ) Effect of exchange rates on cash 0.0 0.1 (0.7 ) 8.1 0.0 7.5 Net (decrease) increase in cash and cash equivalents 0.0 0.1 (0.2 ) (29.2 ) 0.0 (29.3 ) Cash and cash equivalents at beginning of year 0.0 0.0 0.9 50.2 0.0 51.1 Cash and cash equivalents at end of period $ 0.0 $ 0.1 $ 0.7 $ 21.0 $ 0.0 $ 21.8

Description of Business - Addit

Description of Business - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segments	3

Summary of Significant Accoun54

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 30, 2016
Summary Of Significant Accounting Policies [Line Items]
Equity method of investments												$ 0
Foreign currency transaction losses									$ 2,300,000	$ 1,300,000	$ 10,400,000
Period for payment of approval basis sale									30 days
Net sales	$ 366,100,000	$ 384,800,000	$ 378,000,000	$ 346,600,000	$ 313,200,000	$ 371,100,000	$ 385,100,000	$ 346,800,000	$ 1,475,500,000	1,416,200,000	1,626,900,000
Research and development costs									$ 9,000,000	$ 6,600,000	5,200,000
Percentage of LIFO inventory	52.00%				65.00%				52.00%	65.00%
Inventory write-down									$ 400,000	$ 600,000	1,400,000
Goodwill impairment charge	$ 0				$ 0				$ 0	0	67,200,000
China [Member]
Summary Of Significant Accounting Policies [Line Items]
Advance payment received											30,000,000
Agreement period									50 years
Other Current Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Prepaid expenses	$ 18,600,000				$ 17,000,000				$ 18,600,000	17,000,000
Untreated Crosstie Sales [Member]
Summary Of Significant Accounting Policies [Line Items]
Net sales									$ 96,800,000	$ 129,200,000	$ 129,800,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Equity method investment significant influence percent									20.00%
Minimum [Member] | Buildings [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives									10 years
Minimum [Member] | Machinery and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives									3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Equity method investment significant influence percent									50.00%
Maximum [Member] | Buildings [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives									20 years
Maximum [Member] | Machinery and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives									15 years

Summary of Significant Accoun55

Summary of Significant Accounting Policies - Summary of Self-lnsured Liabilities (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Self-insured liabilities at beginning of year	$ 10.9	$ 8
Expense	1.9	5.1
Change in reserves recoverable from insurance	(0.3)	2.4
Reversal of self-insured liabilities	(0.4)	(1.7)
Cash expenditures	(2.6)	(2.9)
Self-insured liabilities at end of year	$ 9.5	$ 10.9

Summary of Significant Accoun56

Summary of Significant Accounting Policies - Summary of Asset Retirement Obligation Liabilities (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]
Asset retirement obligation at beginning of year	$ 36	$ 46.5
Divestiture	0	(8)
Accretion expense	2.4	7.1
Revision in estimated cash flows (a)	9.4	2.7
Cash expenditures	(10.9)	(11.4)
Currency translation	0.2	(0.9)
Balance at end of period	$ 37.1	$ 36

Summary of Significant Accoun57

Summary of Significant Accounting Policies - Summary of Asset Retirement Obligation Liabilities (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Charges related to restructuring activities	$ 9.4	$ 2.7

Summary of Significant Accoun58

Summary of Significant Accounting Policies - Summary of Changes to Deferred Revenue (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Disclosure [Abstract]
Deferred revenue at beginning of year	$ 27.2	$ 30.1
Revenue earned	(0.7)	(0.8)
Currency translation	1.6	(2.1)
Deferred revenue at end of year	$ 28.1	$ 27.2

New Accounting Pronouncements -

New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Increase to additional paid in capital			$ (0.4)	$ (0.5)
Enacted corporate income tax rate		35.00%	35.00%	35.00%
Scenario, Forecast [Member]
Summary Of Significant Accounting Policies [Line Items]
Enacted corporate income tax rate	21.00%
Accounting Standards Update 2016-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Decrease to retained earnings		$ 0.2
Increase to deferred tax assets		0.1
Increase to additional paid in capital		$ 0.3
Accounting Standards Update 2018-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Enacted corporate income tax rate		35.00%
Reclassification of tax effects from AOCI		$ 3.2
Accounting Standards Update 2018-02 [Member] | Scenario, Forecast [Member]
Summary Of Significant Accounting Policies [Line Items]
Enacted corporate income tax rate	21.00%
Accounting Standards Update 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative increase to opening balance of retained earnings		1
Impact of restatement on revenue not recognized		$ 5

Plant Closures and Discontinu60

Plant Closures and Discontinued Operations - Additional Information (Detail)	Dec. 31, 2016	Nov. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	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%	50.00%

Plant Closures and Discontinu61

Plant Closures and Discontinued Operations - Summary of Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	$ 16.1	$ 28.2
Accrual	14.6	13.7
Costs charged against assets	(6.3)	(1.9)
Reversal of accrued charges	(2.1)	(11.2)
Cash paid	(4.8)	(11.7)
Currency translation	0.8	(1)
Reserve, Ending Balance	18.3	16.1
Severance and Employee Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	1.4	2
Accrual	0.9	2.4
Costs charged against assets	0	0
Reversal of accrued charges	(0.3)	(1.9)
Cash paid	(0.3)	(1)
Currency translation	0	(0.1)
Reserve, Ending Balance	1.7	1.4
Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	1.5	4.3
Accrual	2.1	0.1
Costs charged against assets	0	0
Reversal of accrued charges	0	(0.5)
Cash paid	(1.1)	(2.4)
Currency translation	0.2	0
Reserve, Ending Balance	2.7	1.5
Asset Retirement [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	10	21.9
Accrual	4.7	5.6
Costs charged against assets	0	0
Reversal of accrued charges	(1.8)	(8.7)
Cash paid	(2.4)	(8.1)
Currency translation	0.1	(0.7)
Reserve, Ending Balance	10.6	10
Other [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	3.2	0
Accrual	6.9	5.6
Costs charged against assets	(6.3)	(1.9)
Reversal of accrued charges	0	(0.1)
Cash paid	(1)	(0.2)
Currency translation	0.5	(0.2)
Reserve, Ending Balance	$ 3.3	$ 3.2

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016
Related Party Transaction [Line Items]
Loan to related party	$ 0	$ 8.9
Committed Loan Facility Agreements [Member] | Construction Loans [Member] | Koppers Carbon and Chemical Company Limited [Member]
Related Party Transaction [Line Items]
Percentage ownership of subsidiary	75.00%
TKK [Member]
Related Party Transaction [Line Items]
Ownership percentage		30.00%	30.00%
Loan to related party		$ 10
Gain (loss) on sale of equity method investment		$ (1.1)
Gain on repayment of loan by related party	$ 1.3

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Company's Financial Instruments (Detail) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Fair Value [Member]
Financial assets:
Cash and cash equivalents, including restricted cash		$ 60.3	$ 20.8
Investments and other assets	[1]	1.1	1.1
Financial liabilities:
Long-term debt (including current portion)		706.9	669.6
Carrying Value [Member]
Financial assets:
Cash and cash equivalents, including restricted cash		60.3	20.8
Investments and other assets	[1]	1.1	1.1
Financial liabilities:
Long-term debt (including current portion)		$ 688.7	$ 671.1
[1]	Excludes equity method investments.

Earnings per Common Share - Sch

Earnings per Common Share - Schedule of Computation of Basic and Diluted Earnings (Loss) per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income (loss) attributable to Koppers	$ (14.8)	$ 19.8	$ 19.7	$ 4.4	$ 6.4	$ 12.1	$ 12.1	$ (1.3)	$ 29.1	$ 29.3	$ (72)
(Loss) income from discontinued operations									(0.8)	0.6	(0.1)
Income (loss) from continuing operations attributable to Koppers									$ 29.9	$ 28.7	$ (71.9)
Weighted average common shares outstanding:
Basic									20,754	20,636	20,541
Effect of dilutive securities									1,246	419	0
Diluted									22,000	21,055	20,541
Earnings (loss) per common share – continuing operations:
Basic earnings (loss) per common share	$ (0.73)	$ 0.96	$ 1	$ 0.21	$ 0.31	$ 0.59	$ 0.58	$ (0.09)	$ 1.44	$ 1.39	$ (3.50)
Diluted earnings (loss) per common share	$ (0.73)	$ 0.91	$ 0.95	$ 0.20	$ 0.30	$ 0.58	$ 0.57	$ (0.09)	$ 1.36	$ 1.36	$ (3.50)
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share									156	415	668

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future compensation expense related to non-vested stock-based compensation arrangements	$ 15
Future compensation expense, weighted-average expected period of recognition in months	25 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] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	2 years
Restricted Stock Units (RSUs) [Member] | Employees In 2015 and Thereafter Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	4 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
Performance Stock Units [Member] | March 2016 and 2017 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 2017 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 2017 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
Employee Stock Option [Member] | Executive Officer | Grants Prior 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	3 years

Stock-based Compensation - Perf

Stock-based Compensation - Performance Award Fair Value Assumptions (Detail)	12 Months Ended
	Dec. 31, 2017$ / shares
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 - Summ

Stock-based Compensation - Summary of Performance Stock Units (Detail) - shares	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	819,691	834,195
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	581,551	554,388
Minimum [Member] | 2015 - 2017 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	0
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
Target Shares [Member] | 2015 - 2017 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	203,953
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	260,588
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	117,010
Maximum [Member] | 2015 - 2017 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	407,906
Maximum [Member] | 2016 - 2018 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	521,176
Maximum [Member] | 2017 - 2019 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	234,020

Stock-based Compensation - Su68

Stock-based Compensation - Summary of Status and Activity of Non-Vested Stock Awards (Detail)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	834,195
Granted	203,789
Vested	(128,276)
Forfeited	(90,017)
Non-vested, Ending Balance	819,691
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit | $ / shares	$ 23.09
Granted, Weighted Average Grant Date Fair Value per Unit | $ / shares	55.14
Vested, Weighted Average Grant Date Fair Value per Unit | $ / shares	24.99
Forfeited, Weighted Average Grant Date Fair Value per Unit | $ / shares	37.80
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit | $ / shares	$ 29.14
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	279,807
Granted	86,779
Vested	(128,276)
Forfeited	(170)
Non-vested, Ending Balance	238,140
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	554,388
Granted	117,010
Vested	0
Forfeited	(89,847)
Non-vested, Ending Balance	581,551

Stock-based Compensation - Stoc

Stock-based Compensation - Stock Options Fair Value Assumptions (Detail)	12 Months Ended
	Dec. 31, 2017$ / shares
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 - Su70

Stock-based Compensation - Summary of Status and Activity of Stock Options (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options, Outstanding at December 31, 2016 | shares	935,454
Options, Granted | shares	97,403
Options, Exercised | shares	(90,320)
Options, Outstanding at December 31, 2017 | shares	942,537
Options, Exercisable at December 31, 2017 | shares	530,762
Weighted Average Exercise Price per Option, Outstanding at December 31, 2016 | $ / shares	$ 26.10
Weighted Average Exercise Price per Option, Granted | $ / shares	44.10
Weighted Average Exercise Price per Option, Exercised | $ / shares	29.95
Weighted Average Exercise Price per Option, Outstanding at December 31, 2017 | $ / shares	27.59
Weighted Average Exercise Price per Option, Outstanding at December 31, 2017 | $ / shares	$ 30.33
Weighted Average Remaining Contractual Term, Outstanding at December 31, 2017	6 years 2 months 15 days
Weighted Average Remaining Contractual Term, Outstanding at December 31, 2017	4 years 9 months 18 days
Aggregate Intrinsic Value, Outstanding at December 31, 2017 | $	$ 22
Aggregate Intrinsic Value, Outstanding at December 31, 2017 | $	$ 10.9

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Stock-based Compensation Expense Recognized and Cash Received from Exercise of Stock Options (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-based compensation expense recognized:
Less related income tax benefit	$ 4.1	$ 3.6	$ 1.5
Decrease in net income attributable to Koppers	6.5	5.3	2.3
Intrinsic value of exercised stock options	1.3	0.1	0
Cash received from the exercise of stock options	2.7	0.4	0
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense recognized:
Stock-based compensation expense	$ 10.6	$ 8.9	$ 3.8

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)Segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment									3
Net sales	$ 366,100	$ 384,800	$ 378,000	$ 346,600	$ 313,200	$ 371,100	$ 385,100	$ 346,800	$ 1,475,500	$ 1,416,200	$ 1,626,900
Non-U.S. Countries [Member]
Segment Reporting Information [Line Items]
Net sales									$ 623,300	$ 486,900	$ 635,700

Segment Information - Summary o

Segment Information - Summary of Results of Segment Operations (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from external customers:
Net sales		$ 366,100	$ 384,800	$ 378,000	$ 346,600	$ 313,200	$ 371,100	$ 385,100	$ 346,800	$ 1,475,500	$ 1,416,200	$ 1,626,900
Depreciation and amortization expense										49,800	52,900	59,000
Operating profit (loss)		$ 12,200	$ 34,700	$ 37,600	$ 27,600	$ 18,900	$ 27,700	$ 32,000	$ 7,800	112,100	86,400	(29,600)
Capital expenditures (including acquisitions)										67,500	49,900	56,000
Railroad and Utility Products and Services [Member]
Revenues from external customers:
Net sales										512,600	586,500	657,000
Carbon Materials and Chemicals [Member]
Revenues from external customers:
Net sales										551,700	436,300	613,400
Performance Chemicals [Member]
Revenues from external customers:
Net sales										411,200	393,400	356,500
Operating Segments [Member] | Railroad and Utility Products and Services [Member]
Revenues from external customers:
Net sales										512,600	586,500	657,000
Depreciation and amortization expense	[1]									11,800	11,900	14,200
Operating profit (loss)	[2]									25,300	52,500	62,200
Capital expenditures (including acquisitions)										10,600	11,200	11,100
Operating Segments [Member] | Carbon Materials and Chemicals [Member]
Revenues from external customers:
Net sales										551,700	436,300	613,400
Depreciation and amortization expense	[3]									20,100	22,300	25,800
Operating profit (loss)	[4]									27,400	(23,600)	(125,000)
Capital expenditures (including acquisitions)										39,700	29,500	37,600
Operating Segments [Member] | Performance Chemicals [Member]
Revenues from external customers:
Net sales										411,200	393,400	356,500
Depreciation and amortization expense										17,900	18,700	19,000
Operating profit (loss)										71,400	63,500	39,000
Capital expenditures (including acquisitions)										15,400	7,900	5,800
Intersegment [Member]
Revenues from external customers:
Net sales										86,300	98,300	95,400
Intersegment [Member] | Carbon Materials and Chemicals [Member]
Revenues from external customers:
Net sales										79,600	90,200	86,700
Intersegment [Member] | Performance Chemicals [Member]
Revenues from external customers:
Net sales										6,700	8,100	8,700
Corporate, Non-Segment [Member]
Revenues from external customers:
Operating profit (loss)	[5]									(12,000)	(6,000)	(5,800)
Capital expenditures (including acquisitions)										$ 1,800	$ 1,300	$ 1,500
[1]	Excludes impairment charges of $1.9 million in 2015 for a wood treating facility in the United States.
[2]	Includes asset retirement obligation and other restructuring costs of $1.6 million for the restructuring of two facilities in the United States in 2017. Includes asset retirement obligation and other restructuring costs of $6.9 million for the restructuring of three facilities in the United States in 2016. Includes gain on sale of the Company’s North American utility pole business of $3.2 million and restructuring costs of $5.7 million for a wood treating facility in the United States in 2015.
[3]	Excludes impairment charges of $3.7, $3.5 and $12.8 million in 2017, 2016 and 2015, respectively, for CMC.
[4]	Includes plant closure costs of $14.6, $13.2 and $36.5 million in 2017, 2016 and 2015, respectively, for CMC. In the fourth quarter of 2015, the Company also recorded goodwill impairment charges of $67.2 million related to this business unit.
[5]	Operating loss for Corporate includes general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc., pension settlement losses, foreign exchange revaluation related to intercompany loans in connection with a legal reorganization of the Company and acquisition and acquisition-related integration costs.

Segment Information - Summary74

Segment Information - Summary of Results of Segment Operations (Parenthetical) (Detail) - USD ($)	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from External Customer [Line Items]
Impairment charges				$ 3,700,000	$ 3,500,000	$ 14,700,000
Gain (loss) on sale of business				0	2,100,000	3,200,000
Charges related to restructuring activities				9,400,000	2,700,000
Goodwill impairment charge	$ 0	$ 0		0	0	67,200,000
United States [Member]
Revenue from External Customer [Line Items]
Asset retirement obligation and other restructuring costs				1,600,000	6,900,000
Wood Treating Facility [Member] | United States [Member]
Revenue from External Customer [Line Items]
Impairment charges						1,900,000
North American Utility Pole Business [Member]
Revenue from External Customer [Line Items]
Gain (loss) on sale of business						3,200,000
North American Utility Pole Business [Member] | Wood Treating Facility [Member] | United States [Member]
Revenue from External Customer [Line Items]
Charges related to restructuring activities						5,700,000
Carbon Materials and Chemicals [Member]
Revenue from External Customer [Line Items]
Impairment charges				3,700,000	3,500,000	12,800,000
Plant closure cost				$ 14,600,000	$ 13,200,000	36,500,000
Goodwill impairment charge			$ 67,200,000			$ 67,200,000

Segment Information - Summary75

Segment Information - Summary of Tangible and Intangible Assets by Segments (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 1,200,200,000	$ 1,087,500,000
Cash and cash equivalents	60,300,000	20,800,000	$ 21,800,000	$ 51,100,000
Income tax receivable	1,700,000	3,800,000
Deferred taxes	51,900,000	69,100,000
Property, plant and equipment, net	328,000,000	280,800,000
Goodwill	188,200,000	186,400,000	186,600,000
Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	1,157,900,000	1,040,100,000
Corporate, Non-Segment [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Cash and cash equivalents	700,000	0
Income tax receivable	1,700,000	3,800,000
Deferred taxes	29,400,000	32,500,000
Property, plant and equipment, net	5,200,000	4,900,000
Deferred charges	200,000	700,000
Other	5,100,000	5,500,000
Railroad and Utility Products and Services [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Goodwill	10,500,000	9,900,000	9,900,000
Railroad and Utility Products and Services [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	249,700,000	264,200,000
Goodwill	10,500,000	9,900,000
Carbon Materials and Chemicals [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Goodwill			0
Carbon Materials and Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	414,200,000	333,000,000
Performance Chemicals [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Goodwill	177,700,000	176,500,000	$ 176,700,000
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	494,000,000	442,900,000
Goodwill	$ 177,700,000	$ 176,500,000

Segment Information - Schedule

Segment Information - Schedule of Revenues and Long-Lived Assets by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues from external customers	$ 366,100	$ 384,800	$ 378,000	$ 346,600	$ 313,200	$ 371,100	$ 385,100	$ 346,800	$ 1,475,500	$ 1,416,200	$ 1,626,900
Long-lived assets	675,100				622,300				675,100	622,300	644,500
United States [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									852,200	929,300	991,200
Long-lived assets	479,500				446,600				479,500	446,600	460,300
Australia [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									312,800	228,400	280,900
Long-lived assets	131,400				124,300				131,400	124,300	132,900
Europe [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									173,100	140,200	144,000
Long-lived assets	44,800				31,900				44,800	31,900	32,900
Other Countries [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									137,400	118,300	210,800
Long-lived assets	$ 19,400				$ 19,500				$ 19,400	$ 19,500	$ 18,300

Segment Information - Schedul77

Segment Information - Schedule of Segment Revenues for Significant Product Lines (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 366,100	$ 384,800	$ 378,000	$ 346,600	$ 313,200	$ 371,100	$ 385,100	$ 346,800	$ 1,475,500	$ 1,416,200	$ 1,626,900
Railroad and Utility Products and Services [Member]
Segment Reporting Information [Line Items]
Net sales									512,600	586,500	657,000
Railroad and Utility Products and Services [Member] | Railroad Crossties [Member]
Segment Reporting Information [Line Items]
Net sales									326,700	374,000	422,000
Railroad and Utility Products and Services [Member] | Utility Poles [Member]
Segment Reporting Information [Line Items]
Net sales									36,500	34,500	52,400
Railroad and Utility Products and Services [Member] | Creosote [Member]
Segment Reporting Information [Line Items]
Net sales									45,300	49,600	45,700
Railroad and Utility Products and Services [Member] | Rail Joints [Member]
Segment Reporting Information [Line Items]
Net sales									28,200	24,400	28,100
Railroad and Utility Products and Services [Member] | Railroad Infrastructure Services [Member]
Segment Reporting Information [Line Items]
Net sales									34,800	43,400	42,700
Railroad and Utility Products and Services [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales									41,100	60,600	66,100
Carbon Materials and Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales									551,700	436,300	613,400
Carbon Materials and Chemicals [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales									145,300	98,400	145,300
Carbon Materials and Chemicals [Member] | Carbon Pitch [Member]
Segment Reporting Information [Line Items]
Net sales									223,300	191,000	283,400
Carbon Materials and Chemicals [Member] | Creosote and Carbon Black Feedstock [Member]
Segment Reporting Information [Line Items]
Net sales									89,600	71,300	119,600
Carbon Materials and Chemicals [Member] | Phthalic Anhydride [Member]
Segment Reporting Information [Line Items]
Net sales									93,500	75,600	65,100
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales									411,200	393,400	356,500
Performance Chemicals [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales									27,400	27,900	37,900
Performance Chemicals [Member] | Wood Preservative Products [Member]
Segment Reporting Information [Line Items]
Net sales									$ 383,800	$ 365,500	$ 318,600

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Tax Provision (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 11.1	$ (1.9)	$ (4.2)
State	0.6	1.3	0.2
Foreign	15.7	13.3	16
Total current tax provision	27.4	12.7	12
Deferred:
Federal	2.6	(1.6)	(19.2)
State	(1.2)	0.5	3
Foreign	0.2	(0.2)	0
Total deferred tax provision (benefit)	1.6	(1.3)	(16.2)
Total income tax provision (benefit)	$ 29	$ 11.4	$ (4.2)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Income (loss) before income taxes		$ 81.6	$ 48.2	$ (15.2)
Corporate income tax rate		35.00%	35.00%	35.00%
Provisional charge recorded to income tax expense related to corporate income tax rate reduction		$ 7.4
Provisional charge recorded to income tax expense related to one-time transition tax on unrepatriated foreign earnings		13.1
Domestic net operating losses and other tax credits resulting in estimated cash payment		4.7
Unremitted earnings		398
Income tax expense (benefit) relating to copper swap contracts		3.5	$ 8	$ (1.2)
Income tax expense relating to unfunded status of employee post-retirement benefit plans		2.8	2	0.6
Income tax expense related to restricted stock and stock options			0.4	0.5
Valuation allowance		44.5	40.2
Interest expense (income) and related penalties		(0.6)	1.2	$ (1.5)
Accrued interest expense and penalties		3.6	4.2
Unrecognized tax benefits		4
Unrecognized tax benefits with impact on the effective tax rate		4.4	$ 5.7
Valuation Allowance Operating Loss Carryforwards [Member]
Income Taxes [Line Items]
Valuation allowance		$ 5.5
Accounting Standards Update 2018-01 [Member]
Income Taxes [Line Items]
Corporate income tax rate		35.00%
Reclassification of tax effects from AOCI		$ 3.2
Maximum [Member]
Income Taxes [Line Items]
One-time transition tax expected payment in installments period		8 years
Scenario, Forecast [Member]
Income Taxes [Line Items]
Corporate income tax rate	21.00%
Scenario, Forecast [Member] | Accounting Standards Update 2018-01 [Member]
Income Taxes [Line Items]
Corporate income tax rate	21.00%

Income Taxes - Summary of Inc80

Income Taxes - Summary of Income Taxes Reconciled with Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Corporate income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefit	(1.60%)	(0.80%)	2.30%
Foreign earnings taxed at different rates	(21.60%)	(10.10%)	(8.30%)
Transition tax from Tax Act	21.70%	0.00%	0.00%
Deferred tax adjustments from Tax Act	12.30%	0.00%	0.00%
Change in tax contingency reserves	2.20%	6.50%	1.50%
Valuation allowance adjustments	0.90%	(1.90%)	(13.00%)
Domestic production activities deduction	0.00%	0.00%	(0.60%)
Goodwill impairment	0.00%	0.00%	(10.90%)
Deferred tax adjustments	0.00%	(0.20%)	0.40%
Other	(0.80%)	1.10%	(1.10%)
Total effective tax rate	48.10%	29.60%	5.30%

Income Taxes - Summary of Defer

Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Federal and state tax loss carryforwards (expiring from 2018-2036)	$ 21.2	$ 11.3
Tax credits	15	15.4
Reserves, including insurance, environmental and deferred revenue	14.3	22.3
Asset retirement obligations	11.9	12
Pension and other postretirement benefits obligations	10.8	19.2
Foreign tax loss carryforwards (expiring beginning in 2018)	9.3	10.1
Accrued employee compensation	6.3	8.9
Book/tax inventory accounting differences	1.5	3.5
Other	6.1	6.6
Valuation allowance	(44.5)	(40.2)
Total deferred tax assets	51.9	69.1
Deferred tax liabilities:
Tax over book depreciation and amortization	33.2	42.7
Gain on derivative contracts	7	4.2
Other	0.7	1.4
Total deferred tax liabilities	40.9	48.3
Net deferred tax assets	$ 11	$ 20.8

Income Taxes - Summary of Valua

Income Taxes - Summary of Valuation Allowances Recorded to Offset Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Total valuation allowances	$ 44.5	$ 40.2
Foreign [Member] | Tax Credits [Member]
Income Taxes [Line Items]
Total valuation allowances	13.8	14.3
Foreign [Member] | Operating Losses and Capital Losses [Member]
Income Taxes [Line Items]
Total valuation allowances	12	12.7
State [Member] | Operating Losses and Tax Credits [Member]
Income Taxes [Line Items]
Total valuation allowances	$ 18.7	$ 13.2

Income taxes - Summary of Unrec

Income taxes - Summary of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 9.7	$ 7.7	$ 7.2
Additions based on tax provisions related to the current year	0.1	0.9	1.4
Additions for tax provisions of prior years	2.7	1.5	0
Reductions of tax provisions of prior years	(3.4)	0	(0.7)
Reductions as a result of a lapse of the applicable statute of limitations	(0.4)	(0.4)	(0.2)
Balance at end of year	$ 8.7	$ 9.7	$ 7.7

Inventories - Components of Inv

Inventories - Components of Inventories (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 173.6	$ 157.7
Work in process	11.2	14.2
Finished goods	98.4	103.6
Inventories, gross	283.2	275.5
Less revaluation to LIFO	46.3	46.8
Net	$ 236.9	$ 228.7

Equity Investments - Additional

Equity Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Jul. 31, 2015
Schedule of Equity Method Investments [Line Items]
Dividends received from equity method investment		$ 0
Equity loss	$ 1,000,000	2,200,000
KSA Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Sale of assets of equity method investment		2,500,000
Gain (loss) on sale of equity method investment		$ 300,000
Ownership percentage		50.00%	50.00%

Property, Plant and Equipment -

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 837.6	$ 791.2
Less accumulated depreciation	509.6	510.4
Net	328	280.8
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	17.6	17
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	63.4	58.2
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 756.6	$ 716

Property, Plant and Equipment87

Property, Plant and Equipment - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation, including impairment charges	$ 37.5	$ 41.6	$ 58.4
Carbon Materials and Chemicals [Member] | Coal Tar Distillation Plant [Member]
Property, Plant and Equipment [Line Items]
Impairment charges	$ 3.7	$ 3.5	$ 14.7

Goodwill and Other Identifiab88

Goodwill and Other Identifiable Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	$ 186.4	$ 186.6
Currency translation	1.8	(0.2)
Balance ending	188.2	186.4
Railroad and Utility Products and Services [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	9.9	9.9
Currency translation	0.6	0
Balance ending	10.5	9.9
Performance Chemicals [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	176.5	176.7
Currency translation	1.2	(0.2)
Balance ending	$ 177.7	$ 176.5

Goodwill and Other Identifiab89

Goodwill and Other Identifiable Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill And Other Intangible Assets [Line Items]
Goodwill impairment charge	$ 0	$ 0		$ 0	$ 0	$ 67,200,000
Goodwill	188,200,000	186,400,000	$ 186,600,000	188,200,000	186,400,000	186,600,000
Accumulated impairment losses	$ 67,200,000	$ 67,200,000		67,200,000	67,200,000
Amortization expense				14,600,000	$ 14,800,000	15,300,000
Foreign Currency Translation [Member]
Goodwill And Other Intangible Assets [Line Items]
Increase in carrying value of identifiable intangible assets				$ 2,700,000
Carbon Materials and Chemicals [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill impairment charge			67,200,000			67,200,000
Fair value of goodwill			0			0
Goodwill			$ 0			$ 0

Goodwill and Other Identifiab90

Goodwill and Other Identifiable Intangible Assets - Schedule of Identifiable Intangible Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	11 years 1 month 6 days
Gross Carrying Amount	$ 192.6	$ 189.4
Accumulated Amortization	63	47.5
Net	$ 129.6	141.9
Customer Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	12 years 2 months 12 days
Gross Carrying Amount	$ 154.7	152.5
Accumulated Amortization	43.9	33.6
Net	$ 110.8	118.9
Customer Contracts [Member] | Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	9 years
Customer Contracts [Member] | Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	18 years
Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	4 years
Gross Carrying Amount	$ 26.8	26.7
Accumulated Amortization	12.5	8.8
Net	$ 14.3	17.9
Technology [Member] | Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	4 years
Technology [Member] | Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	12 years
Trademarks [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	4 years
Gross Carrying Amount	$ 6.5	6.1
Accumulated Amortization	2.7	1.9
Net	$ 3.8	4.2
Trademarks [Member] | Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	4 years
Trademarks [Member] | Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	7 years
Supply Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	10 years
Weighted average remaining life in years	2 years 2 months 12 days
Gross Carrying Amount	$ 2.5	2.2
Accumulated Amortization	2	1.5
Net	$ 0.5	0.7
Non-Compete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	12 years
Weighted average remaining life in years	6 years 9 months 18 days
Gross Carrying Amount	$ 1.4	1.3
Accumulated Amortization	1.2	1.1
Net	$ 0.2	0.2
Favorable Lease Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	3 years
Weighted average remaining life in years	0 years
Gross Carrying Amount	$ 0.7	0.6
Accumulated Amortization	0.7	0.6
Net	$ 0	$ 0

Goodwill and Other Identifiab91

Goodwill and Other Identifiable Intangible Assets - Schedule of Future Amortization Expense (Detail) $ in Millions	Dec. 31, 2017USD ($)
Goodwill And Intangible Assets Disclosure [Abstract]
2,018	$ 14.5
2,019	14.5
2,020	14.2
2,021	12.3
2,022	$ 9.6

Pensions and Post-Retirement 92

Pensions and Post-Retirement Benefit Plans - Additional Information (Detail) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017USD ($)PlanParticipant	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)PlanParticipant	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2016Participant
Defined Benefit Plan Disclosure [Line Items]
Number of domestic non-qualified defined benefit plans | Plan	3		3
Pension settlement charge			$ (10)	$ (4.4)	$ 0
Defined contribution plan expense			8.9	7.8	6
Amortization of net loss in 2018	$ 1.4		1.4
Accumulated benefit obligation, pension plans	$ 218.7		$ 218.7	243.3
Ultimate health care cost trend rate, year			2,037
Operating expenses			$ 11.2	10.4	9.2
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	6.30%		6.30%
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	4.50%		4.50%
Growth seeking assets [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation investment strategy	30.00%		30.00%
Growth seeking assets [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation investment strategy	40.00%		40.00%
Income generating assets [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation investment strategy	60.00%		60.00%
Income generating assets [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation investment strategy	70.00%		70.00%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total amount paid out of defined benefit plan assets			$ 36.9	13.9
Retiree pension obligations	$ 219.1		219.1	243.6	257.5
Accumulated benefit obligation, pension plans	159.6		159.6	238.5
Expected contributions by employer	$ 4.4		$ 4.4
Pension Benefits [Member] | Domestic Plan [Member] | US [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of salaried terminated deferred vested participants | Participant	100		100			375
Total amount paid out of defined benefit plan assets	$ 3.1			13.9
Pension settlement charge	(1.2)			(4.4)
Pension Benefits [Member] | Domestic Plan [Member] | US [Member] | Qualified Plan [Member] | Annuitize [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension settlement charge		$ (8.8)
Retiree pension obligations		$ 31.3
Percentage of discounted pension obligation		18.00%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total amount paid out of defined benefit plan assets			$ 0	0
Retiree pension obligations	11.1		11.1	$ 10	$ 9.4
Expected contributions by employer	$ 1		$ 1
Initial health care cost trend rate	6.10%		6.10%	6.30%
Salaried and Hourly Employees [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of domestic non-qualified defined benefit plans | Plan	2		2

Pensions and Post-Retirement 93

Pensions and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 1.7	$ 2
Interest cost	9	11	10.9
Expected return on plan assets	(9.6)	(10.5)	(12)
Amortization of prior service cost	0	0	(0.3)
Amortization of net loss	1.9	2.2	6.6
Settlements and curtailments	10	4.4	(0.8)
Net periodic benefit cost	13.3	8.8	6.4
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.1
Interest cost	0.4	0.4	0.4
Expected return on plan assets	0	0	0
Amortization of prior service cost	0	0	(0.1)
Amortization of net loss	(0.2)	(0.4)	(0.3)
Settlements and curtailments	0	0	0
Net periodic benefit cost	$ 0.3	$ 0.1	$ 0.1

Pensions and Post-Retirement 94

Pensions and Post-Retirement Benefit Plans - Schedule of Change in Funded Status of Pension and Post-Retirement Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 200.9
Fair value of plan assets at end of year	188.8	$ 200.9
Noncurrent liabilities	46.3	51.6
Accumulated benefit obligation	218.7	243.3
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	243.6	257.5
Service cost	2	1.7	$ 2
Interest cost	9	11	10.9
Actuarial losses	7.3	10.7
Settlements	(36.9)	(13.9)
Currency translation	5.5	(9.9)
Benefits paid	(11.4)	(13.5)
Benefit obligation at end of year	219.1	243.6	257.5
Fair value of plan assets at beginning of year	200.9	212.4
Actual return on plan assets	19.5	20.8
Employer contribution	11.2	4.5
Settlements	(36.9)	(13.9)
Currency translation	5.5	(9.4)
Benefits paid	(11.4)	(13.5)
Fair value of plan assets at end of year	188.8	200.9	212.4
Funded status of the plan	(30.3)	(42.7)
Noncurrent assets	7	0.8
Current liabilities	1.1	1.1
Noncurrent liabilities	36.2	42.4
Benefit obligation	159.9	238.7
Fair value of plan assets	122.6	195.3
Accumulated benefit obligation	159.6	238.5
Fair value of plan assets	122.6	195.3
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	10	9.4
Service cost	0.1	0.1	0.1
Interest cost	0.4	0.4	0.4
Actuarial losses	1.5	1
Settlements	0	0
Currency translation	0	0
Benefits paid	(0.9)	(0.9)
Benefit obligation at end of year	11.1	10	9.4
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contribution	0.9	0.9
Settlements	0	0
Currency translation	0	0
Benefits paid	(0.9)	(0.9)
Fair value of plan assets at end of year	0	0	$ 0
Funded status of the plan	(11.1)	(10)
Noncurrent assets	0	0
Current liabilities	1	0.8
Noncurrent liabilities	$ 10.1	$ 9.2

Pensions and Post-Retirement 95

Pensions and Post-Retirement Benefit Plans - Schedule of Projected Benefit Payments (Detail) $ in Millions	Dec. 31, 2017USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2,018	$ 11.1
2,019	11
2,020	11.3
2,021	11.5
2,022	11.7
Next five years	64
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2,018	1
2,019	1
2,020	0.9
2,021	0.8
2,022	0.7
Next five years	$ 3.2

Pensions and Post-Retirement 96

Pensions and Post-Retirement Benefit Plans - Schedule of Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.51%	4.09%
Expected return on plan assets	4.62%	5.10%
Rate of compensation increase	3.50%	3.50%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.88%	4.53%
Initial medical trend rate	6.10%	6.30%

Pensions and Post-Retirement 97

Pensions and Post-Retirement Benefit Plans - Schedule of Weighted Average Asset Allocation for Company's Pension Plans (Detail)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	100.00%	100.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	64.00%	71.00%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	30.00%	24.00%
Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	6.00%	5.00%

Pensions and Post-Retirement 98

Pensions and Post-Retirement Benefit Plans - Schedule of Pension Plan Assets at Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 188.8	$ 200.9
Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	63	62.9
Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	114	128
Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	11.8	10
U.S. equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	31.3	25.5
U.S. equity securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	18.6	12.3
U.S. equity securities [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	12.7	13.2
U.S. equity securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
International equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	25.2	23.5
International equity securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	15	12.6
International equity securities [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	10.2	10.9
International equity securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
U.S. debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	76.9	108.1
U.S. debt securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	21.4	29.7
U.S. debt securities [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	53	75.2
U.S. debt securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2.5	3.2
International debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	43.3	33.7
International debt securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	7.5	8.3
International debt securities [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	34.8	24.3
International debt securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1	1.1
Real estate and other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	9.6	6.2
Real estate and other investments [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.5	0
Real estate and other investments [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.8	0.5
Real estate and other investments [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	8.3	5.7
Cash & Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2.5	3.9
Cash & Cash Equivalents [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Cash & Cash Equivalents [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2.5	3.9
Cash & Cash Equivalents [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0	$ 0

Pensions and Post-Retirement 99

Pensions and Post-Retirement Benefit Plans - Summary of Changes in Fair Value of Pension Plan Assets (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 200.9
Fair value of plan assets at end of year	188.8
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	10
Fair value of plan assets at end of year	11.8
Level 3 [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	5.7
Purchases, sales, issuances and settlements	1.9
Realized and unrealized gains	0.7
Fair value of plan assets at end of year	8.3
The amount of total gains during the period attributable to the change in unrealized gains relating to Level 3 net assets still held at the reporting date	0.2
Level 3 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	4.3
Purchases, sales, issuances and settlements	(1.4)
Realized and unrealized gains	0.6
Fair value of plan assets at end of year	3.5
The amount of total gains during the period attributable to the change in unrealized gains relating to Level 3 net assets still held at the reporting date	$ 0.1

Pensions and Post-Retirement100

Pensions and Post-Retirement Benefit Plans - Schedule of Health Care Cost Trend Rates (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Postemployment Benefits [Abstract]
Postretirement benefit expense one-percentage increase	$ 0
Postretirement benefit liability one-percentage increase	0.2
Postretirement benefit expense one-percentage decrease	0
Postretirement benefit liability one-percentage decrease	$ (0.1)

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt Instruments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total debt	$ 688.7	$ 671.1
Less short-term debt and current maturities of long-term debt	11.4	42.6
Less unamortized debt issuance costs	11.7	8.7
Long-term debt	$ 665.6	619.8
Senior Secured Credit Facilities [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.01%
Debt, Maturity	2,022
Total debt	$ 155	100.1
Senior Secured Credit Facilities [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Total debt	$ 0	232.5
Committed Loan Facility Agreements [Member] | Construction Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.80%
Debt, Maturity	2,020
Total debt	$ 33.7	40.4
6.00 percent Senior Notes due 2025 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.00%
Debt, Maturity	2,025
Total debt	$ 500	0
Senior Notes Due 2019 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 0	$ 298.1

Debt - Additional Information (

Debt - Additional Information (Detail) ¥ in Millions	Feb. 15, 2022	Jan. 25, 2017USD ($)	Feb. 28, 2018USD ($)	Feb. 28, 2017USD ($)	Dec. 31, 2017USD ($)Installment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2017CNY (¥)Installment
Debt Instrument [Line Items]
Loss on extinguishment of debt				$ 10,000,000	$ 13,300,000	$ 0	$ 0
Bond premium and bond tender expenses				7,300,000
Write-off unamortized debt issuance cost				2,700,000
Accumulated amortization					1,800,000	12,000,000
Unamortized debt issuance costs					$ 11,700,000	$ 8,700,000
6.00 percent Senior Notes due 2025 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes, offering value		$ 500,000,000
Senior notes, effective percentage		6.00%
Senior notes, payment terms					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.
Debt instrument, redemption price percentage					104.50%
Debt maturity date					Feb. 15, 2025
6.00 percent Senior Notes due 2025 [Member] | Senior Notes [Member] | Scenario, Forecast [Member]
Debt Instrument [Line Items]
Debt instrument, redemption price percentage	101.50%
Senior Secured Credit Facilities [Member]
Debt Instrument [Line Items]
Letters of credit, amount outstanding					$ 41,700,000
Committed Loan Facility Agreements [Member] | Construction Loans [Member]
Debt Instrument [Line Items]
Debt maturity date					Dec. 21, 2020
Number of installments for repayment of loans | Installment					6			6
Installment frequency for repayment of loans					6 months
Commencement period of debt repayment					2018-06
Committed Loan Facility Agreements [Member] | Construction Loans [Member] | Third Party Debt [Member]
Debt Instrument [Line Items]
Construction loan facility borrowing capacity | ¥								¥ 198.8
Committed Loan Facility Agreements [Member] | Construction Loans [Member] | Committed Credit Facility [Member] | Lender [Member]
Debt Instrument [Line Items]
Construction loan facility borrowing capacity | ¥								66.2
Committed Loan Facility Agreements [Member] | Construction Loans [Member] | Koppers Carbon and Chemical Company Limited [Member]
Debt Instrument [Line Items]
Percentage ownership of subsidiary					75.00%
Construction loan facility borrowing capacity					$ 44,000,000			¥ 265
Percentage of non-controlling shareholders					25.00%			25.00%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility				$ 400,000,000
Revolving credit facility, variable interest rate basis				LIBOR
Revolving credit facility, maturity period				2022-02
Write-off unamortized debt issuance cost				$ 3,300,000
Revolving Credit Facility [Member] | Senior Secured Credit Facilities [Member]
Debt Instrument [Line Items]
Debt instrument, unused borrowing capacity					$ 203,300,000
Subsequent Event [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility			$ 600,000,000
Revolving credit facility, variable interest rate basis			LIBOR

Debt - Schedule of Debt Maturit

Debt - Schedule of Debt Maturities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
2,018	$ 11.4
2,019	3
2,020	19.3
2,021	0
2,022	155
Thereafter	500
Total debt	$ 688.7	$ 671.1

Leases - Future Minimum Commitm

Leases - Future Minimum Commitments for Operating Leases (Detail) $ in Millions	Dec. 31, 2017USD ($)
Leases [Abstract]
2,018	$ 43.7
2,019	25.3
2,020	20.6
2,021	16.4
2,022	15.2
Thereafter	50.2
Total	$ 171.4

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leases [Abstract]
Operating lease expense	$ 50.4	$ 50.3	$ 46.4

Derivative Financial Instrum106

Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Maximum period hedged in cash flow hedge	30 months
Unrealized gains, reclassification period	12 months
Unrealized gains, net of tax, expected to be reclassified from other comprehensive income (loss)into earnings	$ 13.3
Fair value of forward contracts credited to other comprehensive income	6.1	$ 12.9	$ (2.2)
Forward Contracts [Member]
Derivative [Line Items]
Forward contracts related to foreign currency designated as cash flow hedges	4.2
Fair value of forward contracts credited to other comprehensive income	0.3
Not designated net fair value - asset (liability)		1
Accrued Liabilities [Member] | Forward Contracts [Member]
Derivative [Line Items]
Not designated gross derivative liability	0.2	0.9
Other Current Assets [Member] | Forward Contracts [Member]
Derivative [Line Items]
Not designated gross derivative assets	$ 0.3	$ 1.9

Derivative Financial Instrum107

Derivative Financial Instruments - Schedule of Outstanding Copper Swap Contracts (Detail) (Detail) - Copper Swap Contracts [Member] £ in Millions, $ in Millions	Dec. 31, 2017USD ($)	Dec. 31, 2017GBP (£)	Dec. 31, 2016USD ($)	Dec. 31, 2016GBP (£)
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding | £		£ 49.1		£ 49.1
Net Fair Value - Asset (Liability) | $	$ 30		$ 11.6
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding | £		37.8		42.6
Net Fair Value - Asset (Liability) | $	25.5		10.6
Not Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding | £		£ 11.3		£ 6.5
Net Fair Value - Asset (Liability) | $	$ 4.5		$ 1

Derivative Financial Instrum108

Derivative Financial Instruments - Schedule of Fair Value of Outstanding Copper Swap Contracts Recorded in Balance Sheet (Detail) - Copper Swap Contracts [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Net Fair Value - Asset (Liability)	$ 30	$ 11.6
Accumulated other comprehensive gain, net of tax	15.8	6.9
Other Current Assets [Member]
Derivative [Line Items]
Net Fair Value - Asset (Liability)	21.8	12.5
Other Assets [Member]
Derivative [Line Items]
Net Fair Value - Asset (Liability)	8.2	0
Accrued Liabilities [Member]
Derivative [Line Items]
Net Fair Value - Asset (Liability)	$ 0	$ (0.9)

Derivative Financial Instrum109

Derivative Financial Instruments - Schedule of Amounts Recognized In Earnings Related To Copper Swap Contracts (Detail) - Copper Swap Contracts [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Gain from contracts not designated as hedges	$ 3.5	$ 1.7
Net	9.1	1.3
Cash Flow Hedging [Member]
Derivative [Line Items]
Gain (loss) from ineffectiveness of cash flow hedges	$ 5.6	$ (0.4)

Derivative Financial Instrum110

Derivative Financial Instruments - Summary of Net Currency Units Outstanding (Detail)	Dec. 31, 2017USD ($)	Dec. 31, 2017GBP (£)	Dec. 31, 2017NZD	Dec. 31, 2017CAD	Dec. 31, 2016USD ($)	Dec. 31, 2016GBP (£)	Dec. 31, 2016NZD	Dec. 31, 2016CAD
Offsetting [Abstract]
Net currency units outstanding	$ 12,500,000	£ 7,000,000	NZD 15,500,000	CAD 2,500,000	$ 24,700,000	£ 7,300,000	NZD 15,500,000	CAD 300,000

Common Stock and Senior Conv111

Common Stock and Senior Convertible Preferred Stock - Schedule of Changes in Senior Convertible Preferred Stock, Common Stock and Treasury Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Senior Convertible Preferred Stock, balance at beginning and end of year	0	0	0
Common Stock, balance at beginning of year	22,140,680	22,016,000	21,938,000
Common Stock, issued for employee stock plans	243,000	125,000	78,000
Common Stock, balance at end of year	22,384,476	22,140,680	22,016,000
Treasury Stock, balance at beginning of year	(1,475,792)	(1,459,000)	(1,443,000)
Treasury Stock, shares repurchased	(130,000)	(17,000)	(16,000)
Treasury Stock, balance at end of year	(1,606,028)	(1,475,792)	(1,459,000)

Commitments and Contingent L112

Commitments and Contingent Liabilities - Additional Information (Detail)	1 Months Ended			12 Months Ended
	Dec. 31, 2017USD ($)PlaintiffCaseParty	Aug. 31, 2017Plaintiff	Jul. 31, 2004USD ($)	Dec. 31, 2017USD ($)StatePlaintiffCasesitePartyPlant	Dec. 31, 2016USD ($)PlaintiffCase	Dec. 31, 2015USD ($)
Loss Contingencies [Line Items]
Number of states with new claims filed | State				2
Number of plaintiffs | Plaintiff	5	5		87	99
Environmental remediation and regulation liability	$ 13,900,000			$ 13,900,000	$ 12,900,000	$ 19,800,000
Accrued liability for environmental matters, current	5,100,000			5,100,000	$ 5,200,000
Portland Harbor and Newark Bay CERCLA sites [Member]
Loss Contingencies [Line Items]
Costs of participating in PRP group	$ 2,200,000			$ 2,200,000
Beazer East [Member]
Loss Contingencies [Line Items]
Environmental legal indemnification expense			$ 7,000,000
Sites listed on National Priorities List | site				1
Compensatory Damages [Member]
Loss Contingencies [Line Items]
Number of cases | Case	48			48
Punitive Damages [Member]
Loss Contingencies [Line Items]
Number of cases | Case	44			44
Indemnification Agreement [Member] | Beazer East [Member]
Loss Contingencies [Line Items]
Environmental remediation costs paid by others, per year				$ 10,000,000
Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases | Case	48			48	55
Reserve for legal proceedings	$ 0			$ 0
Pennsylvania [Member]
Loss Contingencies [Line Items]
Number of cases | Case	47			47
Pennsylvania [Member] | Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases | Case	47			47
Tennessee [Member] | Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases | Case	1			1
Compensatory damages				$ 15,000,000
Oregon [Member] | Portland Harbor CERCLA site [Member]
Loss Contingencies [Line Items]
Number of potential responsible parties | Party	80			80
Net present value of selected remedy estimation				$ 1,100,000,000
Undiscounted cost of selected remedy estimation				1,700,000,000
US [Member] | Performance Chemicals [Member]
Loss Contingencies [Line Items]
Environmental remediation and regulation liability	$ 4,900,000			$ 4,900,000
Number of plant sites | Plant				2
United Kingdom And Australia [Member] | Performance Chemicals [Member]
Loss Contingencies [Line Items]
Environmental remediation and regulation liability	2,800,000			$ 2,800,000
Number of plant sites | Plant				2
Australia [Member] | Continental Carbon facility [Member]
Loss Contingencies [Line Items]
Environmental remediation and regulation liability	$ 2,600,000			$ 2,600,000

Commitments and Contingent L113

Commitments and Contingent Liabilities - Changes in Accrued Liability for Environmental Matters (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Balance at beginning of year	$ 12.9	$ 19.8
Expense	3.2	1.5
Reversal of reserves	(0.7)	(1)
Cash expenditures	(1.8)	(6.3)
Divestitures	0	(0.3)
Currency translation	0.3	(0.8)
Balance at end of period	$ 13.9	$ 12.9

Selected Quarterly Financial114

Selected Quarterly Financial Data - Schedule of Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of operations data:
Net sales	$ 366,100	$ 384,800	$ 378,000	$ 346,600	$ 313,200	$ 371,100	$ 385,100	$ 346,800	$ 1,475,500	$ 1,416,200	$ 1,626,900
Operating profit	12,200	34,700	37,600	27,600	18,900	27,700	32,000	7,800	112,100	86,400	(29,600)
Income (loss) from continuing operations	(14,300)	20,000	20,900	4,700	6,200	12,000	11,300	(2,400)	31,300	27,100	(75,900)
Net income (loss)	(13,800)	19,900	19,800	4,600	6,300	11,900	11,300	(1,800)	30,500	27,700	(76,000)
Net income (loss) attributable to Koppers	$ (14,800)	$ 19,800	$ 19,700	$ 4,400	$ 6,400	$ 12,100	$ 12,100	$ (1,300)	$ 29,100	$ 29,300	$ (72,000)
Basic -
Continuing operations	$ (0.73)	$ 0.96	$ 1	$ 0.21	$ 0.31	$ 0.59	$ 0.58	$ (0.09)	$ 1.44	$ 1.39	$ (3.50)
Discontinued operations	0.02	0	(0.06)	0	0	0	0	0.03	(0.04)	0.03	(0.01)
Earnings (loss) per basic common share	(0.71)	0.96	0.94	0.21	0.31	0.59	0.58	(0.06)	1.40	1.42	(3.51)
Diluted -
Continuing operations	(0.73)	0.91	0.95	0.20	0.30	0.58	0.57	(0.09)	1.36	1.36	(3.50)
Discontinued operations	0.02	0	(0.05)	0	0	0	0	0.03	(0.04)	0.03	(0.01)
Earnings (loss) per diluted common share	(0.71)	0.91	0.90	0.20	0.30	0.58	0.57	(0.06)	1.32	1.39	$ (3.51)
Maximum [Member]
Diluted -
Price range of common stock	51.80	46.55	44.80	45.85	42.70	33.71	31.35	23.43	51.80	42.70
Minimum [Member]
Diluted -
Price range of common stock	$ 45.75	$ 35.17	$ 33.90	$ 39.10	$ 31.28	$ 28.54	$ 21.38	$ 13.58	$ 33.90	$ 13.58

Selected Quarterly Financial115

Selected Quarterly Financial Data - Schedule of Selected Quarterly Financial Data (Parenthetical) (Detail) $ in Millions	3 Months Ended
	Dec. 31, 2017USD ($)
Quarterly Financial Information Disclosure [Abstract]
Increase in income tax expense	$ 20.5

Subsidiary Guarantor Informa116

Subsidiary Guarantor Information for Koppers Inc. 2025 Notes and Shelf Registration - Additional Information (Detail) - USD ($)	Jan. 25, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Senior Notes [Member] | 6.00 percent Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Principal value of Senior Notes	$ 500,000,000
Domestic Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Cash dividends paid		$ 3,800,000	$ 1,200,000	$ 6,500,000
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Percentage ownership of subsidiary	100.00%
Koppers Inc. [Member]
Debt Instrument [Line Items]
Amount of restricted net assets unavailable for distribution		31,000,000
Koppers Inc. [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Amount of assets exceeded liabilities		$ 100,100,000

Subsidiary Guarantor Informa117

Subsidiary Guarantor Information for Koppers Inc. 2025 Notes and Shelf Registration - Condensed Consolidating Statement of Comprehensive Income (Loss) (Detail) - USD ($)	1 Months Ended	3 Months Ended								12 Months Ended
	Feb. 28, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Statement Of Income Captions [Line Items]
Net sales		$ 366,100,000	$ 384,800,000	$ 378,000,000	$ 346,600,000	$ 313,200,000	$ 371,100,000	$ 385,100,000	$ 346,800,000	$ 1,475,500,000	$ 1,416,200,000	$ 1,626,900,000
Cost of sales including depreciation and amortization										1,220,100,000	1,200,900,000	1,467,900,000
Loss on pension settlements										10,000,000	4,400,000	0
Gain on sale of business										0	(2,100,000)	(3,200,000)
Goodwill impairment		0				0				0	0	67,200,000
Selling, general and administrative										133,300,000	126,600,000	124,600,000
Operating profit (loss)		12,200,000	34,700,000	37,600,000	27,600,000	18,900,000	27,700,000	32,000,000	7,800,000	112,100,000	86,400,000	(29,600,000)
Other income (loss)										4,000,000	2,900,000	200,000
Equity income of subsidiaries										0	0	0
Interest (income) expense										42,500,000	50,800,000	50,700,000
Loss on extinguishment of debt	$ 10,000,000									13,300,000	0	0
Income taxes										29,000,000	11,400,000	(4,200,000)
Income (loss) from continuing operations		(14,300,000)	20,000,000	20,900,000	4,700,000	6,200,000	12,000,000	11,300,000	(2,400,000)	31,300,000	27,100,000	(75,900,000)
Discontinued operations										(800,000)	600,000	(100,000)
Noncontrolling interests										1,400,000	(1,600,000)	(4,000,000)
Net income (loss) attributable to Koppers		$ (14,800,000)	$ 19,800,000	$ 19,700,000	$ 4,400,000	$ 6,400,000	$ 12,100,000	$ 12,100,000	$ (1,300,000)	29,100,000	29,300,000	(72,000,000)
Comprehensive income (loss) attributable to Koppers										60,700,000	40,500,000	(91,500,000)
Consolidation Eliminations [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales										(83,300,000)	(99,800,000)	(100,700,000)
Cost of sales including depreciation and amortization										(82,100,000)	(101,200,000)	(99,400,000)
Loss on pension settlements										0	0
Gain on sale of business											0	0
Goodwill impairment												0
Selling, general and administrative										0	0	0
Operating profit (loss)										(1,200,000)	1,400,000	(1,300,000)
Other income (loss)										(1,200,000)	(1,800,000)	(2,000,000)
Equity income of subsidiaries										(198,800,000)	(145,600,000)	97,800,000
Interest (income) expense										(1,200,000)	(1,800,000)	(2,000,000)
Loss on extinguishment of debt										0
Income taxes										(100,000)	0	(300,000)
Income (loss) from continuing operations										(199,900,000)	(144,200,000)	96,800,000
Discontinued operations										0	0	0
Noncontrolling interests										0	0	0
Net income (loss) attributable to Koppers										(199,900,000)	(144,200,000)	96,800,000
Comprehensive income (loss) attributable to Koppers										(283,800,000)	(155,900,000)	150,200,000
Parent [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales										0	0	0
Cost of sales including depreciation and amortization										0	0	0
Loss on pension settlements										0	0
Gain on sale of business											0	0
Goodwill impairment												0
Selling, general and administrative										1,900,000	1,900,000	1,900,000
Operating profit (loss)										(1,900,000)	(1,900,000)	(1,900,000)
Other income (loss)										0	0	0
Equity income of subsidiaries										30,300,000	30,600,000	(70,800,000)
Interest (income) expense										0	0	0
Loss on extinguishment of debt										0
Income taxes										(700,000)	(600,000)	(700,000)
Income (loss) from continuing operations										29,100,000	29,300,000	(72,000,000)
Discontinued operations										0	0	0
Noncontrolling interests										0	0	0
Net income (loss) attributable to Koppers										29,100,000	29,300,000	(72,000,000)
Comprehensive income (loss) attributable to Koppers										60,700,000	40,500,000	(91,500,000)
Koppers Inc. [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales										590,600,000	660,700,000	791,100,000
Cost of sales including depreciation and amortization										570,900,000	637,400,000	771,700,000
Loss on pension settlements										10,000,000	4,400,000
Gain on sale of business											0	(3,200,000)
Goodwill impairment												43,100,000
Selling, general and administrative										47,700,000	43,300,000	41,300,000
Operating profit (loss)										(38,000,000)	(24,400,000)	(61,800,000)
Other income (loss)										500,000	300,000	500,000
Equity income of subsidiaries										103,800,000	79,100,000	900,000
Interest (income) expense										39,000,000	47,600,000	45,800,000
Loss on extinguishment of debt										13,300,000
Income taxes										(16,400,000)	(23,200,000)	(35,400,000)
Income (loss) from continuing operations										30,400,000	30,600,000	(70,800,000)
Discontinued operations										0	0	0
Noncontrolling interests										0	0	0
Net income (loss) attributable to Koppers										30,400,000	30,600,000	(70,800,000)
Comprehensive income (loss) attributable to Koppers										61,800,000	41,300,000	(90,300,000)
Domestic Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales										344,900,000	350,600,000	335,600,000
Cost of sales including depreciation and amortization										235,000,000	252,300,000	233,200,000
Loss on pension settlements										0	0
Gain on sale of business											0	0
Goodwill impairment												24,100,000
Selling, general and administrative										43,300,000	38,200,000	37,800,000
Operating profit (loss)										66,600,000	60,100,000	40,500,000
Other income (loss)										2,400,000	4,100,000	4,100,000
Equity income of subsidiaries										64,700,000	35,900,000	(27,900,000)
Interest (income) expense										0	0	0
Loss on extinguishment of debt										0
Income taxes										30,000,000	22,200,000	15,800,000
Income (loss) from continuing operations										103,700,000	77,900,000	900,000
Discontinued operations										0	0	0
Noncontrolling interests										0	0	0
Net income (loss) attributable to Koppers										103,700,000	77,900,000	900,000
Comprehensive income (loss) attributable to Koppers										132,800,000	85,000,000	(18,100,000)
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales										623,300,000	504,700,000	600,900,000
Cost of sales including depreciation and amortization										496,300,000	412,400,000	562,400,000
Loss on pension settlements										0	0
Gain on sale of business											(2,100,000)	0
Goodwill impairment												0
Selling, general and administrative										40,400,000	43,200,000	43,600,000
Operating profit (loss)										86,600,000	51,200,000	(5,100,000)
Other income (loss)										2,300,000	300,000	(2,400,000)
Equity income of subsidiaries										0	0	0
Interest (income) expense										4,700,000	5,000,000	6,900,000
Loss on extinguishment of debt										0
Income taxes										16,200,000	13,000,000	16,400,000
Income (loss) from continuing operations										68,000,000	33,500,000	(30,800,000)
Discontinued operations										(800,000)	600,000	(100,000)
Noncontrolling interests										1,400,000	(1,600,000)	(4,000,000)
Net income (loss) attributable to Koppers										65,800,000	35,700,000	(26,900,000)
Comprehensive income (loss) attributable to Koppers										$ 89,200,000	$ 29,600,000	$ (41,800,000)

Subsidiary Guarantor Informa118

Subsidiary Guarantor Information for Koppers Inc. 2025 Notes and Shelf Registration - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Cash and cash equivalents	$ 60.3	$ 20.8	$ 21.8	$ 51.1
Receivables, net	160.9	140.6
Affiliated receivables	0	0
Inventories, net	236.9	228.7
Deferred tax assets	0
Other current assets	48.6	48
Total current assets	506.7	438.1
Equity investments	0	0
Property, plant and equipment, net	328	280.8
Goodwill	188.2	186.4	186.6
Intangible assets, net	129.6	141.9
Deferred tax assets	18.4	27.1
Affiliated loan receivables	0	0
Other assets	29.3	13.2
Total assets	1,200.2	1,087.5
LIABILITIES AND EQUITY
Accounts payable	141.9	144.2
Affiliated payables	0	0
Accrued liabilities	127.9	106.3
Current maturities of long-term debt	11.4	42.6
Total current liabilities	281.2	293.1
Long-term debt	665.6	619.8
Affiliated debt	0	0
Other long-term liabilities	147.6	140
Total liabilities	1,094.4	1,052.9
Koppers shareholders’ equity	99.9	30.4
Noncontrolling interests	5.9	4.2
Total liabilities and equity	1,200.2	1,087.5
Consolidation Eliminations [Member]
Assets
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0
Affiliated receivables	75.1	(83.1)
Inventories, net	(1.9)	(0.8)
Deferred tax assets	0.1
Other current assets	0.2	0.3
Total current assets	73.5	(83.6)
Equity investments	(1,092.3)	(922.7)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Deferred tax assets	0	0
Affiliated loan receivables	(280.6)	(264.1)
Other assets	0	0
Total assets	(1,299.4)	(1,270.4)
LIABILITIES AND EQUITY
Accounts payable	0	0
Affiliated payables	74.3	(91.2)
Accrued liabilities	0	0
Current maturities of long-term debt	0	0
Total current liabilities	74.3	(91.2)
Long-term debt	0	0
Affiliated debt	(280.6)	(264.1)
Other long-term liabilities	0	0
Total liabilities	(206.3)	(355.3)
Koppers shareholders’ equity	(1,093.1)	(915.1)
Noncontrolling interests	0	0
Total liabilities and equity	(1,299.4)	(1,270.4)
Parent [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0
Affiliated receivables	0.6	0.7
Inventories, net	0	0
Deferred tax assets	0
Other current assets	0	0
Total current assets	0.6	0.7
Equity investments	99.3	29.9
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Deferred tax assets	0	0
Affiliated loan receivables	0	0
Other assets	0	0
Total assets	99.9	30.6
LIABILITIES AND EQUITY
Accounts payable	0	0.2
Affiliated payables	0	0
Accrued liabilities	0	0
Current maturities of long-term debt	0	0
Total current liabilities	0	0.2
Long-term debt	0	0
Affiliated debt	0	0
Other long-term liabilities	0	0
Total liabilities	0	0.2
Koppers shareholders’ equity	99.9	30.4
Noncontrolling interests	0	0
Total liabilities and equity	99.9	30.6
Koppers Inc. [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0.7	0	0.1	0
Receivables, net	48.6	50.8
Affiliated receivables	19.4	34.8
Inventories, net	80.4	106.6
Deferred tax assets	0
Other current assets	6.6	5.1
Total current assets	155.7	197.3
Equity investments	716.3	697.4
Property, plant and equipment, net	155.2	126.7
Goodwill	0.8	0.8
Intangible assets, net	7.2	7.9
Deferred tax assets	29.4	29.7
Affiliated loan receivables	34.9	36.9
Other assets	4.4	5.5
Total assets	1,103.9	1,102.2
LIABILITIES AND EQUITY
Accounts payable	65.1	69.6
Affiliated payables	(90.3)	46
Accrued liabilities	59.9	49.5
Current maturities of long-term debt	0.1	30.2
Total current liabilities	34.8	195.3
Long-term debt	643.3	592
Affiliated debt	233.7	209.9
Other long-term liabilities	92	75
Total liabilities	1,003.8	1,072.2
Koppers shareholders’ equity	100.1	30
Noncontrolling interests	0	0
Total liabilities and equity	1,103.9	1,102.2
Domestic Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0	0	0.7	0.9
Receivables, net	27.7	25.4
Affiliated receivables	(83)	32.2
Inventories, net	40.5	23.9
Deferred tax assets	0
Other current assets	23	13.4
Total current assets	8.2	94.9
Equity investments	276.8	195.4
Property, plant and equipment, net	47.3	39.6
Goodwill	153.1	153.1
Intangible assets, net	96.7	107.1
Deferred tax assets	(13.2)	(8.4)
Affiliated loan receivables	224.3	205.3
Other assets	15.3	6.1
Total assets	808.5	793.1
LIABILITIES AND EQUITY
Accounts payable	32.4	38.9
Affiliated payables	13.8	20.7
Accrued liabilities	16.4	18.9
Current maturities of long-term debt	0	0
Total current liabilities	62.6	78.5
Long-term debt	0	0
Affiliated debt	19.3	23.5
Other long-term liabilities	14.4	11.6
Total liabilities	96.3	113.6
Koppers shareholders’ equity	712.2	679.5
Noncontrolling interests	0	0
Total liabilities and equity	808.5	793.1
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	59.6	20.8	$ 21	$ 50.2
Receivables, net	84.6	64.4
Affiliated receivables	(12.1)	15.4
Inventories, net	117.9	99
Deferred tax assets	(0.1)
Other current assets	18.8	29.2
Total current assets	268.7	228.8
Equity investments	(0.1)	0
Property, plant and equipment, net	125.5	114.5
Goodwill	34.3	32.5
Intangible assets, net	25.7	26.9
Deferred tax assets	2.2	5.8
Affiliated loan receivables	21.4	21.9
Other assets	9.6	1.6
Total assets	487.3	432
LIABILITIES AND EQUITY
Accounts payable	44.4	35.5
Affiliated payables	2.2	24.5
Accrued liabilities	51.6	37.9
Current maturities of long-term debt	11.3	12.4
Total current liabilities	109.5	110.3
Long-term debt	22.3	27.8
Affiliated debt	27.6	30.7
Other long-term liabilities	41.2	53.4
Total liabilities	200.6	222.2
Koppers shareholders’ equity	280.8	205.6
Noncontrolling interests	5.9	4.2
Total liabilities and equity	$ 487.3	$ 432

Subsidiary Guarantor Informa119

Subsidiary Guarantor Information for Koppers Inc. 2025 Notes and Shelf Registration - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	$ 101.8	$ 119.5	$ 127.7
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(67.5)	(49.9)	(56)
Repayments (loans to) from affiliates	0	0	0
Repayment of loan	9.5	0	0
Net cash proceeds (payments) from divestitures and asset sales	1.5	(3.8)	14.9
Net cash used in investing activities	(56.5)	(53.7)	(41.1)
Cash provided by (used in) financing activities:
(Repayments) borrowings of long-term debt	7.6	(61.4)	(113.4)
Borrowings (repayments) of affiliated debt	0	0	0
Deferred financing costs	(11)	(1.4)	(1)
Dividends paid	0	0	(8.7)
Stock (repurchased) issued	(2.5)	0.1	(0.3)
Net cash (used in) provided by financing activities	(5.9)	(62.7)	(123.4)
Effect of exchange rates on cash	0.1	(4.1)	7.5
Net increase (decrease) in cash and cash equivalents	39.5	(1)	(29.3)
Cash and cash equivalents at beginning of period	20.8	21.8	51.1
Cash and cash equivalents at end of period	60.3	20.8	21.8
Consolidation Eliminations [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	(117.5)	(93.1)	(56.9)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0	0
Repayments (loans to) from affiliates	(81.7)	(19.8)	(10.4)
Repayment of loan	0
Net cash proceeds (payments) from divestitures and asset sales	0	0	0
Net cash used in investing activities	(81.7)	(19.8)	(10.4)
Cash provided by (used in) financing activities:
(Repayments) borrowings of long-term debt	(0.1)	0	0
Borrowings (repayments) of affiliated debt	81.7	19.8	10.4
Deferred financing costs	0	0	0
Dividends paid	117.6	93.1	56.9
Stock (repurchased) issued	0	0	0
Net cash (used in) provided by financing activities	199.2	112.9	67.3
Effect of exchange rates on cash	0	0	0
Net increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	0	0	0
Parent [Member] | Reportable Legal Entities [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	2.5	(0.1)	5.4
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0	0
Repayments (loans to) from affiliates	0	0	0
Repayment of loan	0
Net cash proceeds (payments) from divestitures and asset sales	0	0	0
Net cash used in investing activities	0	0	0
Cash provided by (used in) financing activities:
(Repayments) borrowings of long-term debt	0	0	0
Borrowings (repayments) of affiliated debt	0	0	0
Deferred financing costs	0	0	0
Dividends paid	0	0	(5.1)
Stock (repurchased) issued	(2.5)	0.1	(0.3)
Net cash (used in) provided by financing activities	(2.5)	0.1	(5.4)
Effect of exchange rates on cash	0	0	0
Net increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	0	0	0
Koppers Inc. [Member] | Reportable Legal Entities [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	116.8	106.6	63
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(42.2)	(30.1)	(41.2)
Repayments (loans to) from affiliates	(0.6)	(6.9)	6.3
Repayment of loan	0
Net cash proceeds (payments) from divestitures and asset sales	0.1	0	12.3
Net cash used in investing activities	(42.7)	(37)	(22.6)
Cash provided by (used in) financing activities:
(Repayments) borrowings of long-term debt	17	(59.9)	(104.2)
Borrowings (repayments) of affiliated debt	(75.6)	(7.2)	71
Deferred financing costs	(11)	(1.4)	(1)
Dividends paid	(3.8)	(1.2)	(6.2)
Stock (repurchased) issued	0	0	0
Net cash (used in) provided by financing activities	(73.4)	(69.7)	(40.4)
Effect of exchange rates on cash	0	0	0.1
Net increase (decrease) in cash and cash equivalents	0.7	(0.1)	0.1
Cash and cash equivalents at beginning of period	0	0.1	0
Cash and cash equivalents at end of period	0.7	0	0.1
Domestic Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	39.3	77	55.9
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(13.5)	(7.1)	(5.3)
Repayments (loans to) from affiliates	64.2	16.9	(5.1)
Repayment of loan	0
Net cash proceeds (payments) from divestitures and asset sales	1	0.9	2.1
Net cash used in investing activities	51.7	10.7	(8.3)
Cash provided by (used in) financing activities:
(Repayments) borrowings of long-term debt	0	0.1	0.1
Borrowings (repayments) of affiliated debt	9.1	(6.5)	(6.4)
Deferred financing costs	0	0	0
Dividends paid	(100.1)	(82)	(40.8)
Stock (repurchased) issued	0	0	0
Net cash (used in) provided by financing activities	(91)	(88.4)	(47.1)
Effect of exchange rates on cash	0	0	(0.7)
Net increase (decrease) in cash and cash equivalents	0	(0.7)	(0.2)
Cash and cash equivalents at beginning of period	0	0.7	0.9
Cash and cash equivalents at end of period	0	0	0.7
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	60.7	29.1	60.3
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(11.8)	(12.7)	(9.5)
Repayments (loans to) from affiliates	18.1	9.8	9.2
Repayment of loan	9.5
Net cash proceeds (payments) from divestitures and asset sales	0.4	(4.7)	0.5
Net cash used in investing activities	16.2	(7.6)	0.2
Cash provided by (used in) financing activities:
(Repayments) borrowings of long-term debt	(9.3)	(1.6)	(9.3)
Borrowings (repayments) of affiliated debt	(15.2)	(6.1)	(75)
Deferred financing costs	0	0	0
Dividends paid	(13.7)	(9.9)	(13.5)
Stock (repurchased) issued	0	0	0
Net cash (used in) provided by financing activities	(38.2)	(17.6)	(97.8)
Effect of exchange rates on cash	0.1	(4.1)	8.1
Net increase (decrease) in cash and cash equivalents	38.8	(0.2)	(29.2)
Cash and cash equivalents at beginning of period	20.8	21	50.2
Cash and cash equivalents at end of period	$ 59.6	$ 20.8	$ 21

Schedule II - Valuation and 120

Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 3.8	$ 6.5	$ 5.6
Business Acquisition	0	0	0
Increase to Expense	0.4	0.7	1.3
Net Write-Offs	(1.8)	(3.4)	0
Currency Translation	0.1	0	(0.4)
Balance at End of Year	2.5	3.8	6.5
Deferred Tax Valuation Allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	40.2	41.9	32.4
Business Acquisition	0	0	0
Increase to Expense	4	0.9	10.1
Net Write-Offs	(0.5)	(1.5)	0
Currency Translation	0.8	(1.1)	(0.6)
Balance at End of Year	$ 44.5	$ 40.2	$ 41.9