Koppers (KOP) 10-Q 3 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	KOP
Entity Registrant Name	Koppers Holdings Inc.
Entity Central Index Key	1,315,257
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		21,116,559

Condensed Consolidated Statemen

Condensed Consolidated Statement of Operations and Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net sales		$ 406.1	$ 346.6
Cost of sales (excluding items below)		311.4	274.9
Depreciation and amortization		11.8	11.2
Impairment and restructuring charges		1.5	1.5
Selling, general and administrative expenses		38.1	30.9
Operating profit	[1]	43.3	28.1
Other income		0.2	1.5
Interest expense		10.5	10.6
Loss on extinguishment of debt		0	13.3
Income before income taxes		33	5.7
Income tax provision		9.2	1
Income from continuing operations		23.8	4.7
Loss from discontinued operations, net of tax benefit of $0.0		(0.1)	(0.1)
Net income		23.7	4.6
Net income attributable to noncontrolling interests		5.9	0.2
Net income attributable to Koppers		$ 17.8	$ 4.4
Earnings per common share attributable to Koppers common shareholders:
Basic -		$ 0.86	$ 0.21
Diluted -		$ 0.81	$ 0.20
Comprehensive income		$ 16.2	$ 12.3
Comprehensive income attributable to noncontrolling interests		6.1	0.2
Comprehensive income attributable to Koppers		$ 10.1	$ 12.1
Weighted average shares outstanding (in thousands):
Basic		20,894	20,722
Diluted		22,158	21,746
[1]	Operating loss for Corporate includes primarily general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc.

Condensed Consolidated Stateme3

Condensed Consolidated Statement of Operations and Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Loss from discontinued operations, net of tax benefit	$ 0	$ 0

Condensed Consolidated Balance

Condensed Consolidated Balance Sheet - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 52.2	$ 60.3
Accounts receivable, net of allowance of $2.5	212.4	159.2
Income tax receivable	2	1.7
Inventories, net	243.2	236.9
Other current assets	39.9	48.6
Total current assets	549.7	506.7
Property, plant and equipment, net	352.9	328
Goodwill	222.5	188.2
Intangible assets, net	145.1	129.6
Deferred tax assets	21	18.4
Other assets	24.8	29.3
Total assets	1,316	1,200.2
Liabilities
Accounts payable	148	141.9
Accrued liabilities	109.8	127.9
Current maturities of long-term debt	7.9	11.4
Total current liabilities	265.7	281.2
Long-term debt	782.9	665.6
Accrued postretirement benefits	46.4	46.3
Deferred tax liabilities	7.5	7.3
Other long-term liabilities	94.9	94
Total liabilities	1,197.4	1,094.4
Commitments and contingent liabilities (Note 18)
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; 22,901,622 and 22,384,476 shares issued	0.2	0.2
Additional paid-in capital	194.7	190.6
Retained earnings	21.6	7.4
Accumulated other comprehensive loss	(44.2)	(40.1)
Treasury stock, at cost, 1,785,063 and 1,606,028 shares	(65.6)	(58.2)
Total Koppers shareholders’ equity	106.7	99.9
Noncontrolling interests	11.9	5.9
Total equity	118.6	105.8
Total liabilities and equity	$ 1,316	$ 1,200.2

Condensed Consolidated Balance5

Condensed Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Accounts receivable, allowance	$ 2.5	$ 2.5
Senior Convertible Preferred Stock, par value	$ 0.01	$ 0.01
Senior Convertible Preferred Stock, shares authorized	10,000,000	10,000,000
Senior Convertible Preferred Stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	80,000,000	80,000,000
Common Stock, shares issued	22,901,622	22,384,476
Treasury stock, shares	1,785,063	1,606,028

Condensed Consolidated Stateme6

Condensed Consolidated Statement of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash provided by (used in) operating activities:
Net income	$ 23.7	$ 4.6
Adjustments to reconcile net cash provided by (used in) operating activities:
Depreciation and amortization	11.8	11.2
Loss on extinguishment of debt	0	13.3
Gain on disposal of assets and investment	0.1	(1.3)
Deferred income taxes	(0.1)	0.1
Change in other liabilities	(1.4)	(2.3)
Non-cash interest expense	0.5	0.5
Stock-based compensation	2.9	2.3
Other - net	3.2	(1.2)
Changes in working capital:
Accounts receivable	(41.7)	(27.8)
Inventories	(10.7)	(8.5)
Accounts payable	2.4	(7.8)
Accrued liabilities	(20.2)	(9.8)
Other working capital	0.5	2.6
Net cash used in operating activities	(29)	(24.1)
Cash (used in) provided by investing activities:
Capital expenditures	(22.5)	(14.9)
Acquisitions, net of cash acquired	(62.9)	0
Repayments received on loan	0	9.5
Net cash provided by divestitures and asset sales	0.3	0.5
Net cash used in investing activities	(85.1)	(4.9)
Cash provided by (used in) financing activities:
Net increase in revolving credit facility borrowings	116.9	80.7
Borrowings of long-term debt	0.3	500
Repayments of long-term debt	(4.1)	(538.5)
Issuances of Common Stock	1.3	1.6
Repurchases of Common Stock	(7.4)	(1.3)
Payment of debt issuance costs	(1.1)	(11)
Net cash (used in) provided by financing activities	105.9	31.5
Effect of exchange rate changes on cash	0.1	0.1
Net (decrease) increase in cash and cash equivalents	(8.1)	2.6
Cash and cash equivalents at beginning of period	60.3	20.8
Cash and cash equivalents at end of period	$ 52.2	$ 23.4

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	1. Basis of Presentation The accompanying unaudited condensed consolidated financial statements and related disclosures have been prepared in accordance with accounting principles generally accepted in the United States applicable to interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation of Koppers Holdings Inc.’s and its subsidiaries’ (“Koppers”, “Koppers Holdings” or the “Company”) financial position and interim results as of and for the periods presented have been included. All such adjustments are of a normal recurring nature unless disclosed otherwise. Because the Company’s business is seasonal, results for interim periods are not necessarily indicative of those that may be expected for a full year. The Condensed Consolidated Balance Sheet for December 31, 2017 has been summarized from the audited balance sheet contained in the Annual Report on Form 10-K for the year ended December 31, 2017. Certain prior period amounts in the notes to the consolidated financial statements have been reclassified to conform to the current period’s presentation. The financial information included herein should be read in conjunction with the Company’s audited consolidated financial statements and related notes included in its Annual Report on Form 10-K for the year ended December 31, 2017.

New Accounting Pronouncements

New Accounting Pronouncements	3 Months Ended
	Mar. 31, 2018
Accounting Changes And Error Corrections [Abstract]
New Accounting Pronouncements	2. New Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) or services. Subsequent to the issuance of ASU 2014-09, the FASB issued multiple ASUs which either amended or clarified ASU 2014-09. Collectively, the revenue recognition ASUs were effective for annual reporting periods beginning after December 15, 2017. The Company elected to use the modified retrospective method for transition in which the cumulative effect was recognized at our January 1, 2018 date of adoption with no restatement of comparative periods presented. The implementation of the guidance had no material impact on the measurement of recognition of revenue of prior periods; however, additional disclosures have been added in accordance with the ASU. In August 2017, the FASB issued ASU No. 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities.” This ASU amends and simplifies existing guidance in order to allow companies to more accurately present the economic effects of risk management activities in the financial statements. The Company adopted this ASU effective January 1, 2018 and the Company reclassified a $3.6 million unrealized gain, net of tax, from retained earnings to accumulated other comprehensive loss upon adoption. In March 2017, the FASB issued ASU 2017-07, “Compensation – Retirement Benefits (Topic 715)”, in order to improve the presentation of net periodic pension and postretirement costs. The amendment requires that an employer report the service cost component in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The amendments in this update related to income statement activity are applied. As a practical expedient, the Company has used the amounts disclosed in its pension and post-retirement benefits footnote as the estimation basis for applying the retrospective presentation requirements. The Company adopted this ASU effective January 1, 2018, and for retrospective presentation, reclassified $0.4 million In January 2017, the FASB issued ASU No. 2017-04, “Simplifying the Test for Goodwill Impairment (Topic 350).” The update is intended to simplify how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. The amendments in this update are effective for periods beginning after December 15, 2019. Entities are required to apply the amendments in this update prospectively from the date of adoption, with early adoption permitted. The Company adopted this ASU effective January 1, 2018. In August 2016, the FASB The Company adopted this ASU effective January 1, 2018 In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842).” ASU 2016-02 requires an entity to recognize a right-of-use asset and lease liability for all leases with terms of more than one year. Recognition, measurement and presentation of expenses will depend on classification as a finance or operating lease. The standard is effective January 1, 2019 and requires a modified retrospective adoption. The Company has a project team analyzing all of its leases to determine the impact of the adoption of ASU 2016-02 will have on its consolidated financial statements expected to be completed during the third quarter of 2018, but anticipates that it will result in a significant right-of-use asset and related lease liability to be recognized on our consolidated balance sheet as certain of our manufacturing facilities, offices and equipment are currently categorized as operating leases.

Plant Closures and Divestitures

Plant Closures and Divestitures	3 Months Ended
	Mar. 31, 2018
Discontinued Operations And Disposal Groups [Abstract]
Plant Closures and Divestitures	3. Plant Closures and Divestitures 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 at its Follansbee, West Virginia coal tar distillation facility in the second half of 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 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 Site demolition Other Total (Dollars in millions) Reserve at December 31, 2016 $ 1.4 $ 1.5 $ 10.0 $ 3.2 $ 16.1 Accrual 0.9 2.1 4.7 6.9 14.6 Cost charged against assets 0.0 0.0 0.0 (6.3 ) (6.3 ) Reversal of accrued charges (0.3 ) 0.0 (1.8 ) 0.0 (2.1 ) Cash paid (0.3 ) (1.1 ) (2.4 ) (1.0 ) (4.8 ) Currency translation 0.0 0.2 0.1 0.5 0.8 Reserve at December 31, 2017 $ 1.7 $ 2.7 $ 10.6 $ 3.3 $ 18.3 Accrual 0.0 0.9 0.3 1.2 2.4 Cost charged against assets 0.0 0.0 0.0 (1.1 ) (1.1 ) Cash paid 0.0 (0.2 ) (1.8 ) (0.1 ) (2.1 ) Currency translation 0.0 (0.1 ) 0.0 0.0 (0.1 ) Reserve at March 31, 2018 $ 1.7 $ 3.3 $ 9.1 $ 3.3 $ 17.4

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
Acquisitions	4. Acquisitions On February 28, 2018, Koppers Inc. acquired M.A. Energy Resources, LLC. (“MAER”) for cash consideration of $66.1 million. The purchase price was funded by borrowings on Koppers Inc.’s credit facility. MAER is a vertically-integrated company that provides material recovery services for crossties that have been taken out of service and other biomass material. MAER converts this recovered material into alternative fuels, such as crosstie-derived fuel or biomass-derived fuel, that is used as a substitute for conventional higher-cost carbon-based fuel. MAER currently operates three processing facilities, each of which is located to serve its Class I railroad customer base. MAER’s revenues were $30 million for the year ended December 31, 2017. The Company has completed a preliminary valuation analysis to determine the fair values of MAER’s assets and liabilities. Accordingly, the financial statements include a preliminary fair value determination based on assumptions and estimates that, while considered reasonable, are subject to changes, which may be material. Upon completion of detailed valuation analyses, there may be additional increases or decreases to the recorded fair values of the acquired assets and liabilities, including but not limited to receivables, inventories, trademarks, customer relationships and other intangible assets, and property, plant and equipment that could give rise to future amounts of depreciation and amortization expense and changes in related deferred taxes that are not reflected in the information contained in this unaudited condensed consolidated information. Accordingly, once the necessary valuation analyses have been performed and the final fair value determination has been completed, actual results may differ materially from the information presented in this unaudited condensed consolidated financial information. The preliminary valuation of identifiable assets acquired and liabilities assumed upon the acquisition of MAER are shown in the table below. February 28, 2018 (Dollars in millions) Cash and cash equivalents $ 3.2 Accounts receivable 4.9 Other current assets 0.3 Property, plant and equipment 6.6 Intangibles 19.3 Goodwill 34.1 Total assets acquired 68.4 Accounts payable & accrued expenses 2.3 Net assets acquired $ 66.1 Goodwill of $34.1 million has been allocated to our Railroad and Utility Products and Services segment. The Company expects that a significant portion of the goodwill recognized will be deductible for tax purposes, but this determination is dependent upon the finalization of the purchase price allocation process. Net assets acquired included intangible assets with respect to customer relationships of $18.7 million which will be amortized over a period of 12 years and a tradename of $0.6 million which will be amortized over a period of two years. The intangible assets other than goodwill are classified in “Intangible assets, net” in the condensed consolidated balance sheet. Events subsequent to March 31, 2018 Cox Industries – On April 10, 2018, Koppers Inc. acquired Cox Industries, Inc. (“Cox”) in a cash transaction for approximately $200 million. The transaction was funded by borrowings on Koppers Inc.’s revolving credit facility discussed in “Note 14 - Debt.” Cox is a manufacturer of treated utility transmission and distribution poles for utility companies and cooperative utility companies. It is also a manufacturer of pilings used for construction and marine applications. Cox manufactures and sells poles and pilings through a network of eight manufacturing facilities and 19 distribution yards located throughout the United States. Cox treats its products with a variety of wood protection chemicals, including copper chromium arsenate and creosote which is produced by the Company’s Performance Chemicals and CMC segments, respectively.

Revenue Recognition

Revenue Recognition	3 Months Ended
	Mar. 31, 2018
Revenue From Contract With Customer [Abstract]
Revenue Recognition	5. Revenue Recognition On January 1, 2018, we adopted the new accounting standard Topic 606, and all the related amendments to all contracts using the modified retrospective method. We recognized the cumulative effect of initially applying the new revenue standard as an adjustment to the opening balance of retained earnings. The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. The Company has identified certain contracts with customers where revenue has been accelerated upon adoption of ASU 2014-09 as the related performance obligations under the contract have been satisfied and control of the goods or services have been transferred to the customer. The Company calculated the cumulative effect to the opening balance of retained earnings recognized at January 1, 2018 to be an increase of $0.3 million, including $5.3 million in revenue not previously recognized during the year ended December 31, 2017. Revenue accelerated for the three months ending March 31, 2018 from the adoption of ASC 606 was $4.0 million and, as such, the net impact of adopting ASC 606 for the three months ending March 31, 2018 was a decrease in revenue and cost of goods sold of $1.3 million and $1.2 million, respectively, and was 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. Refer to “Note 9 – Segment Information” for relevant disaggregation of revenue. Revenue is recognized upon the completion of performance obligations under the Company’s contracts with customers and when control of a good or service is transferred to the customer. Substantially all of the Company’s contracts with its customers are ship and invoice arrangements where revenue is recognized when we transfer control to the customer which is at the time of shipment or delivery. Contract Balances The timing of revenue recognition in accordance with ASC 606 and subsequent billings related to such revenue recognized results in both billed accounts receivable and unbilled receivables (contract assets), both classified as accounts receivable, net of allowance within the condensed consolidated balance sheet. For certain contracts with customers within our RUPS and CMC segments, amounts are billed as specific performance obligations are fulfilled in accordance with agreed-upon contractual terms. For these contracts with customers, revenue is recognized prior to billings, resulting in contract assets. Contract assets recorded within accounts receivable, net of allowance within the condensed consolidated balance sheet as of March 31, 2018 and January 1, 2018 due to performance obligations being fulfilled prior to billing was $18.7 million and $5.3 million, respectively.

Comprehensive Income and Equity

Comprehensive Income and Equity	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Comprehensive Income and Equity	6. Comprehensive Income and Equity Total comprehensive income for the three months ended March 31, 2018 and 2017 is summarized in the table below: Three Months Ended March 31, 2018 2017 (Dollars in millions) Net income $ 23.7 $ 4.6 Other comprehensive income: Change in currency translation adjustment 1.2 6.1 Unrealized (loss) gain on cash flow hedges, net of tax benefit (expense) of $4.9 and $(0.9) (9.3 ) 1.3 Change in accounting standard 0.3 0.0 Unrecognized pension net loss, net of tax expense of $0.1 and $0.2 0.3 0.3 Total comprehensive income 16.2 12.3 Less: Comprehensive income attributable to noncontrolling interests 6.1 0.2 Comprehensive income attributable to Koppers $ 10.1 $ 12.1 Amounts reclassified from accumulated other comprehensive loss to net income consist of amounts shown for changes in unrecognized pension net loss. This component of accumulated other comprehensive income is included in the computation of net periodic pension cost as disclosed in “Note 13 – Pensions and Postretirement Benefit Plans”. Other amounts reclassified from accumulated other comprehensive loss include income related to derivative financial instruments, net of tax, of $2.5 million The following tables present the change in equity for the three months ended March 31, 2018 and 2017, respectively: (Dollars in millions) Total Koppers Shareholders’ Equity Noncontrolling Interests Total Equity Balance at December 31, 2017 $ 99.9 $ 5.9 $ 105.8 Net income 17.8 5.9 23.7 Issuance of common stock 1.3 0.0 1.3 Employee stock plans 2.8 0.0 2.8 Other comprehensive (loss) income (7.7 ) 0.1 (7.6 ) Repurchases of common stock (7.4 ) 0.0 (7.4 ) Balance at March 31, 2018 $ 106.7 $ 11.9 $ 118.6 (Dollars in millions) Total Koppers Shareholders’ Equity Noncontrolling Interests Total Equity Balance at December 31, 2016 $ 30.4 $ 4.2 $ 34.6 Net income 4.4 0.2 4.6 Issuance of common stock 1.6 0.0 1.6 Employee stock plans 2.4 0.0 2.4 Other comprehensive income 7.7 0.0 7.7 Repurchases of common stock (1.3 ) 0.0 (1.3 ) Balance at March 31, 2017 $ 45.2 $ 4.4 $ 49.6

Earnings per Common Share

Earnings per Common Share	3 Months Ended
	Mar. 31, 2018
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 per common share: Three Months Ended March 31, 2018 2017 (Dollars in millions, except share amounts, in thousands, and per share amounts) Net income attributable to Koppers $ 17.8 $ 4.4 Less: Loss from discontinued operations (0.1 ) (0.1 ) Income from continuing operations attributable to Koppers $ 17.9 $ 4.5 Weighted average common shares outstanding: Basic 20,894 20,722 Effect of dilutive securities 1,264 1,024 Diluted 22,158 21,746 Income per common share – continuing operations: Basic income per common share $ 0.86 $ 0.21 Diluted income per common share 0.81 0.20 Other data: Antidilutive securities excluded from computation of diluted earnings per common share 8 128

Stock-based Compensation

Stock-based Compensation	3 Months Ended
	Mar. 31, 2018
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, 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 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 prior to 2016 have vesting based upon a performance condition. These performance stock units generally have three-year performance objectives and all performance stock units have a three-year period for vesting (if the applicable performance objective is achieved). For awards granted prior to 2016, 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 2015 exceeded the maximum value creation and vested at 200 percent in March 2018. Performance stock units granted in 2016 and thereafter 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 & Poor’s 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 March 2016 Grant Grant date price per share of performance award $ 41.60 $ 44.10 $ 18.11 Expected dividend yield per share 0.00 % 0.00 % 0.00 % Expected volatility 39.40 % 43.50 % 40.86 % Risk-free interest rate 2.35 % 1.54 % 0.96 % Look-back period in years 2.84 2.83 2.84 Grant date fair value per share of performance award $ 47.12 $ 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 March 31, 2018: Performance Period Minimum Shares Target Shares Maximum Shares 2016 – 2018 0 256,628 513,256 2017 – 2019 0 115,098 230,196 2018 – 2020 0 123,133 246,266 The following table shows a summary of the status and activity of non-vested stock units for the three months ended March 31, 2018: Restricted Stock Units Performance Stock Units Total Stock Units Weighted Grant Date Fair Value per Unit Non-vested at December 31, 2017 238,140 581,551 819,691 $ 29.14 Granted 85,346 124,262 209,608 $ 44.78 Performance share adjustment 0 204,866 204,866 $ 17.57 Vested (73,576 ) (409,732 ) (483,308 ) $ 18.64 Forfeited (3,965 ) (6,088 ) (10,053 ) $ 37.74 Non-vested at March 31, 2018 245,945 494,859 740,804 $ 37.09 Stock Options Stock options to most executive officers vest and become exercisable in four equal annual installments. The stock options have a term of ten years. In the event of termination of employment, other than retirement, death or disability, any non-vested options are forfeited. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the options over the service period will result. There are special vesting provisions for the stock options related to a change in control. 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 2016 Grant March 2015 Grant Grant date price per share of stock option award $ 41.60 $ 44.10 $ 18.11 $ 17.57 Expected dividend yield per share 0.00 % 0.00 % 0.00 % 3.40 % Expected life in years 5.73 5.77 5.96 5.75 Expected volatility 37.05 % 39.70 % 40.86 % 42.27 % Risk-free interest rate 2.67 % 2.13 % 1.45 % 1.73 % Grant date fair value per share of option award $ 16.38 $ 17.90 $ 7.41 $ 5.20 The Company suspended its dividend in February 2015 and does not expect to declare any dividends for the foreseeable future. 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 three months ended March 31, 2018: Options Weighted Exercise Price per Option Weighted Average Remaining Contractual Term (in years) Aggregate Value (in millions) Outstanding at December 31, 2017 942,537 $ 27.59 Granted 139,012 $ 41.60 Exercised (32,568 ) $ 39.41 Outstanding at March 31, 2018 1,048,981 $ 29.08 6.49 $ 13.1 Exercisable at March 31, 2018 653,320 $ 27.88 5.55 $ 8.8 Stock Compensation Expense Total stock-based compensation expense recognized for three months ended March 31, 2018 and 2017 is as follows: Three Months Ended March 31, 2018 2017 (Dollars in millions) Stock-based compensation expense recognized: Selling, general and administrative expenses $ 2.9 $ 2.3 Less related income tax benefit 1.0 0.9 Decrease in net income attributable to Koppers $ 1.9 $ 1.4 Intrinsic value of exercised stock options $ 0.2 $ 0.7 Cash received from the exercise of stock options $ 0.9 $ 1.6 As of March 31, 2018, total future gross compensation expense related to non-vested stock-based compensation arrangements, which are expected to vest, totaled $23.7 million and the weighted-average period over which this cost is expected to be recognized is approximately 30 months.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2018
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 and a business related to the recovery of used crossties. Utility products include the treating of transmission and distribution poles and pilings. In February 2018, the Company acquired MAER, recovered material into alternative fuels, such as crosstie-derived fuel or biomass-derived fuel, that is used as a substitute for conventional higher-cost carbon-based fuel. 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 as disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. Refer to “Note 5 – Revenue Recognition” for accounting policies specific to revenue recognition. 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: Three Months Ended March 31, 2018 2017 (Dollars in millions) Revenues from external customers: Railroad and Utility Products and Services $ 108.4 $ 135.5 Performance Chemicals 97.4 96.7 Carbon Materials and Chemicals 200.3 114.4 Total $ 406.1 $ 346.6 Intersegment revenues: Performance Chemicals $ 1.8 $ 1.7 Carbon Materials and Chemicals 18.2 18.9 Total $ 20.0 $ 20.6 Depreciation and amortization expense: Railroad and Utility Products and Services $ 3.0 $ 3.0 Performance Chemicals 4.4 4.4 Carbon Materials and Chemicals 4.4 3.8 Total $ 11.8 $ 11.2 Operating profit (loss): Railroad and Utility Products and Services $ 1.1 $ 9.3 Performance Chemicals 5.6 18.6 Carbon Materials and Chemicals 37.2 0.6 Corporate (a) (0.6 ) (0.4 ) Total $ 43.3 $ 28.1 (a) Operating loss for Corporate includes primarily general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc. The following table sets forth revenues for significant product lines, net of all intersegment transactions, for the Company’s segments for the periods indicated: Three Months Ended March 31, 2018 2017 (Dollars in millions) Railroad and Utility Products and Services: Railroad treated products $ 79.4 $ 108.7 Utility poles 11.5 10.8 Rail joints 8.3 7.4 Railroad infrastructure services 7.0 8.6 Other products 2.2 0.0 108.4 135.5 Performance Chemicals: Wood preservative products 95.0 93.6 Other products 2.4 3.1 97.4 96.7 Carbon Materials and Chemicals: Pitch and related products 129.2 48.2 Creosote and distillates 22.9 20.5 Phthalic anhydride and other chemicals 22.2 20.3 Naphthalene 13.1 9.1 Other products 12.9 16.3 200.3 114.4 Total $ 406.1 $ 346.6 The following table sets forth certain tangible and intangible assets allocated to each of the Company’s segments as of the dates indicated: March 31, 2018 December 31, 2017 (Dollars in millions) Segment assets: Railroad and Utility Products and Services $ 330.2 $ 249.7 Performance Chemicals 496.0 494.0 Carbon Materials and Chemicals 447.0 414.2 All other 42.8 42.3 Total $ 1,316.0 $ 1,200.2 Goodwill: Railroad and Utility Products and Services $ 44.5 $ 10.5 Performance Chemicals 178.0 177.7 Total $ 222.5 $ 188.2

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes Effective Tax Rate The income tax provision for interim periods is comprised of an estimated annual effective income tax rate applied to current year ordinary income and tax associated with discrete items. These discrete items generally relate to excess stock compensation deductions, changes in tax laws, adjustments to uncertain tax positions and changes of estimated tax to the actual liability determined upon filing tax returns. To determine the annual effective tax rate, management is required to make estimates of annual pretax income in each domestic and foreign jurisdiction in which the Company conducts business. Entities that have historical pre-tax losses and current year estimated pre-tax losses that are not projected to generate a future benefit are excluded from the estimated annual effective income tax rate. 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 with changes that are effective in 2017 and 2018. Changes in tax rates and tax laws and their impact on deferred taxes are accounted for in the period of legislative enactment. In March 2018, the FASB issued Accounting Standards Update (ASU) 2018-05, which codified guidance provided in SEC Staff Accounting Bulletin 118. ASU 2018-05 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. ASU 2018-05 applies to measuring the impact of tax laws effecting the period of enactment, such as the change in the corporate income The Tax Act imposes a one-time transition tax on unrepatriated earnings of foreign subsidiaries through December 31, 2017 that have not previously been subject to federal tax. The Company estimated this one-time transition tax and recorded a provisional charge to income tax expense of $13.1 million in 2017. This amount has been further reduced by domestic losses and other tax credits resulting in an estimated cash payment of approximately $4.7 million that the Company expects to elect to pay in installments over the next eight years. The Company has not yet completed its calculation of the total post-1986 unrepatriated earnings for its foreign subsidiaries and this calculation will not be finalized until the Company’s 2017 federal income tax return is filed. Further, the transition tax is based in part on the amount of those earnings held in cash and other specified assets, which is a defined term under the Tax Act and other provisions that remain subject to interpretation. The Company continues its analysis of the effects of the Tax Act and will continue to gather additional information related to these provisional amounts. Such additional analysis includes collecting and refining necessary data and interpreting additional guidance issued by the tax authorities and other standard-setting bodies. During the three months ended March 31, 2018, there were no changes made to the provisional amounts recorded in 2017. Any adjustments to the Company’s estimates may materially impact its income tax expense in the period in which the adjustments are made. The Tax Act introduces a new provision for U.S. taxation of 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. This GILTI provision is effective for 2018. The Company has elected to treat the effect of this GILTI provision as a period expense in the year incurred and has included an estimate of the impact in its estimated annual effective income tax rate. We will continue to analyze this GILTI provision and any tax planning opportunities that may be available to reduce the impact of the GILTI provision. As a result, it is possible that our current estimate of the impact of this GILTI provision may materially change. The Tax Act introduces other new provisions that are effective for 2018 and changes how certain provisions are calculated beginning in 2018. Other than the GILTI provision, we do not expect that any of these new provisions or changes will have a material impact to the Company’s tax expense. The estimated annual effective income tax rate, excluding discrete items discussed above, was 34.4 percent and 27.0 percent for the three months ended March 31, 2018 and 2017, respectively. The estimated annual effective income tax rate differs from the U.S. federal statutory tax rate due to: March 31, 2018 March 31, 2017 Federal income tax rate 21.0 % 35.0 % State income taxes, net of federal tax benefit 0.9 1.7 Foreign earnings taxed at different rates 3.5 (11.3 ) Valuation allowance adjustments (5.7 ) 0.0 Change in tax contingency reserves 0.1 0.2 GILTI inclusion (net of foreign tax credits) 13.1 0.0 Other 1.5 1.4 Estimated annual effective income tax rate 34.4 % 27.0 % The estimated annual effective income tax rate includes the benefit of a valuation allowance adjustment for one of our Chinese entities. Management determined that sufficient positive evidence exists to support that this entity’s net operating losses are more likely than not to be realized. Income taxes as a percentage of pretax income were 27.9 percent for the three months ended March 31, 2018. This is lower than the estimated annual effective income tax rate due to discrete items. Discrete items included in income taxes for the three months ended March 31, 2018 were a net benefit of $2.2 million, which is primarily related to excess tax benefits for stock-based compensation. Income taxes as a percentage of pretax income were 17.5 percent for the three months ended March 31, 2017. This is lower than the estimated annual effective income tax rate due to discrete items, but also because the estimated annual effective income tax rate is applied to pre-tax earnings excluding the results of our Chinese entities that were not expected to generate a future tax benefit. Discrete items included in income taxes for the three months ended March 31, 2017 were a net benefit of $0.4 million, which includes excess tax benefits for stock-based compensation of $0.8 million offset by additional accruals for uncertain tax positions of $0.4 million. During the year, management regularly updates estimates of pre-tax income and income tax expense based on changes in pre-tax income projections by taxable jurisdiction, repatriation of foreign earnings, uncertain tax positions and other tax matters. To the extent that actual results vary from these estimates, the actual annual effective income tax rate at the end of the year could be materially different from the estimated annual effective income tax rate for the three months ended March 31, 2018. Uncertain Tax Positions 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, state and local, or non-U.S. income tax examinations by tax authorities for years prior to 2014. Unrecognized tax benefits totaled $8.8 million and $8.7 million as of March 31, 2018 and December 31, 2017, respectively. As of March 31, 2018 and December 31, 2017, the total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate, was approximately $4.5 million and $4.4 million, respectively. The Company recognizes interest expense and any related penalties from uncertain tax positions in income tax expense. As of March 31, 2018 and December 31, 2017, the Company had accrued approximately $3.8 million and $3.6 million for interest and penalties, 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 Company does not anticipate significant increases to the amount of unrecognized tax benefits within the next twelve months.

Inventories

Inventories	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Inventories	11. Inventories Net inventories as of March 31, 2018 and December 31, 2017 are summarized in the table below: March 31, 2018 December 31, 2017 (Dollars in millions) Raw materials $ 180.1 $ 173.6 Work in process 10.9 11.2 Finished goods 100.1 98.4 $ 291.1 $ 283.2 Less revaluation to LIFO 47.9 46.3 Net $ 243.2 $ 236.9

Property, Plant and Equipment

Property, Plant and Equipment	3 Months Ended
	Mar. 31, 2018
Property Plant And Equipment [Abstract]
Property, Plant and Equipment	12. Property, Plant and Equipment Property, plant and equipment as of March 31, 2018 and December 31, 2017 are summarized in the table below: March 31, 2018 December 31, 2017 (Dollars in millions) Land $ 17.7 $ 17.6 Buildings 64.4 63.4 Machinery and equipment 790.4 756.6 $ 872.5 $ 837.6 Less accumulated depreciation 519.6 509.6 Net $ 352.9 $ 328.0 Impairments – There were no impairment charges incurred for the three months ended March 31, 2018 and 2017.

Pensions and Post-Retirement Be

Pensions and Post-Retirement Benefit Plans	3 Months Ended
	Mar. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Pensions and Post-Retirement Benefit Plans	13. 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. The following table provides the components of net periodic benefit cost for the pension plans for the three months ended March 31, 2018 and 2017: Three Months Ended March 31, 2018 2017 (Dollars in millions) Service cost $ 0.5 $ 0.5 Interest cost 1.8 2.4 Expected return on plan assets (2.1 ) (2.5 ) Amortization of net loss 0.4 0.5 Net periodic benefit cost $ 0.6 $ 0.9 Defined contribution plan expense $ 2.0 $ 2.2

Debt

Debt	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Debt	14. Debt Debt as of March 31, 2018 and December 31, 2017 was as follows: Weighted Average Interest Rate Maturity March 31, 2018 December 31, 2017 (Dollars in millions) Revolving Credit Facility 4.34 % 2022 $ 271.9 $ 155.0 Construction and other loans 4.78 % 2020 31.1 33.7 Senior Notes due 2025 6.00 % 2025 500.0 500.0 Debt 803.0 688.7 Less short-term debt and current maturities of long-term debt 7.9 11.4 Less unamortized debt issuance costs 12.2 11.7 Long-term debt $ 782.9 $ 665.6 Senior Notes due 2025 The 2025 Notes are senior obligations, are unsecured and are guaranteed by Koppers Holdings Inc. and certain of Koppers Inc.’s domestic subsidiaries. The 2025 Notes pay interest semi-annually in arrears on February 15 and August 15 beginning on August 15, 2017 and will mature on February 15, 2025 unless earlier redeemed or repurchased. On or after February 15, 2020, the Company is entitled to redeem all or a portion of the 2025 Senior Notes at a redemption price of 104.5 percent of principal value, declining to a redemption price of 101.5 percent on or after February 15, 2022 until the redemption price is equivalent to the principal value on 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 original maturity date was 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. On February 26, 2018, the Company amended its $400.0 million Revolving Credit Facility to increase its capacity to $600.0 million. Terms under the amended Revolving Credit Facility are substantially consistent with the original Revolving Credit Facility. As of March 31, 2018, the Company had $268.1 million of unused revolving credit availability for working capital purposes after restrictions from certain letter of credit commitments and other covenants. As of March 31, 2018, $35.4 million of commitments were utilized by outstanding letters of credit. Loss on Extinguishment of Debt In February 2017, all of the outstanding Koppers Inc. senior notes due 2019 were repurchased at a premium to carrying value and accordingly, the Company realized a loss on extinguishment of debt totaling $10.0 million consisting of $7.3 million for bond premium and bond tender expenses and $2.7 million for the write-off of unamortized debt issuance costs. Also in February 2017, Koppers Inc. repaid its term loan in full and entered into a new Revolving Credit Facility. Accordingly, the Company realized a loss of $3.3 million for the write-off of unamortized debt issuance costs. Construction Loans The Company’s 75-percent owned subsidiary 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. Events subsequent to March 31, 2018 On April 10, 2018, the Company amended its $600.0 million Revolving Credit Facility to enter into a new Secured Term Loan Facility. The new Secured Term Loan Facility includes the $600.0 million Revolving Credit Facility and a secured term loan of $100.0 million with a quarterly amortization of $2.5 million and a five-year maturity. In addition, the maturity date of the amended Revolving Credit Facility is extended one year to February 2023. The interest rate on the amended Revolving Credit Facility is variable and is based on LIBOR. The initial average borrowing rates under both facilities are expected to be approximately five percent. Terms under the amended Revolving Credit Facility are substantially consistent with the original Revolving Credit Facility.

Asset Retirement Obligations

Asset Retirement Obligations	3 Months Ended
	Mar. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	15. Asset Retirement Obligations The Company recognizes asset retirement obligations for the removal and disposal of residues; dismantling of certain tanks required by governmental authorities; cleaning and dismantling costs for owned rail cars; cleaning costs for leased rail cars and barges; and site demolition, when required by governmental authorities or by contract. The following table reflects changes in the carrying values of asset retirement obligations: March 31, 2018 December 31, 2017 (Dollars in millions) Asset retirement obligation at beginning of year $ 37.1 $ 36.0 Accretion expense 0.4 2.4 Revision in estimated cash flows 0.0 9.4 Cash expenditures (2.1 ) (10.9 ) Currency translation 0.1 0.2 Balance at end of period $ 35.5 $ 37.1

Deferred Revenue

Deferred Revenue	3 Months Ended
	Mar. 31, 2018
Deferred Revenue Disclosure [Abstract]
Deferred Revenue	16. Deferred Revenue The Company defers revenues associated with extended product warranty liabilities based on historical loss experience and sales of extended warranties on certain products. The following table reflects changes in the carrying values of deferred revenue: March 31, 2018 December 31, 2017 (Dollars in millions) Balance at beginning of year $ 28.1 $ 27.2 Revenue earned (0.2 ) (0.7 ) Currency translation 0.8 1.6 Balance at end of period $ 28.7 $ 28.1 Deferred revenue classified in other long-term liabilities in the consolidated balance sheet totaled $27.9 million as of March 31, 2018 and $27.2 million as of December 31, 2017 with the remainder classified in accrued liabilities.

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2018
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	17. Derivative Financial Instruments The Company utilizes derivative instruments to manage exposures to risks that have been identified and measured and are capable of being controlled. The primary risks managed by the company by using derivative instruments are commodity price risk associated with copper and foreign currency exchange risk associated with a number of currencies, principally the U.S. dollar, the Canadian dollar, the New Zealand dollar, the Euro and British pounds. Swap contracts on copper are used to manage the price risk associated with forecasted purchases of materials used in the Company’s manufacturing processes. Generally, the Company will not hedge cash flow exposures for durations longer than 36 months and the Company has hedged certain volumes of copper through December 2019. The Company enters into foreign currency forward contracts to manage foreign currency risk associated with the Company’s receivable and payable balances and foreign currency denominated sales. Generally, the Company enters into master netting arrangements with the counterparties and offsets net derivative positions with the same counterparties. Currently, the Company’s agreements do not require cash collateral. ASC Topic 815-10, “Derivatives and Hedging,” requires companies to recognize all derivative instruments as either assets or liabilities at fair value in the balance sheet. Derivative instruments’ fair value is determined using significant other observable inputs, or Level 2 in the fair value hierarchy. In accordance with ASC Topic 815-10, the Company designates certain of its commodity swaps as cash flow hedges of forecasted purchases of commodities and certain of its foreign currency swaps as cash flow hedges of forecasted sales. For derivative instruments that are designated and qualify as cash flow hedges, the effective portion of the gain or loss on the derivative is reported as a component of other comprehensive income and is reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative instruments representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current earnings. The amount of hedge ineffectiveness charged to profit and loss is reported in the table below. For those commodity and foreign currency swaps which are not designated as cash flow hedges, the fair value of the swap is recognized as an asset or liability in the consolidated balance sheet and the related gain or loss on the derivative is reported in current earnings. As of March 31, 2018 and December 31, 2017, the Company has outstanding copper swap contracts of the following amounts: Units Outstanding (in Pounds) Net Fair Value - Asset March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 (Amounts in millions) Cash flow hedges 39.8 37.8 $ 13.8 $ 25.5 Not designated as hedges 12.9 11.3 1.0 4.5 Total 52.7 49.1 $ 14.8 $ 30.0 As of March 31, 2018 and December 31, 2017, the fair value of the outstanding copper swap contracts is recorded in the balance sheet as follows: March 31, 2018 December 31, 2017 (Dollars in millions) Other current assets $ 12.7 $ 21.8 Other assets 3.5 8.2 Accrued liabilities (1.4 ) 0.0 Net asset on balance sheet $ 14.8 $ 30.0 Accumulated other comprehensive gain, net of tax $ 10.5 $ 15.8 Based upon contracts outstanding at March 31, 2018, in the next twelve months the Company estimates that $7.7 million of unrealized gains, net of tax, related to commodity price hedging will be reclassified from other comprehensive income into earnings. See Note 6 – Comprehensive Income and Equity, for amounts recorded in other comprehensive income and for amounts reclassified from accumulated other comprehensive income to net income for the periods specified below. For the three months ended March 31, 2018 and 2017, the following amounts were recognized in earnings related to copper swap contracts: Three Months Ended March 31, 2018 2017 (Dollars in millions) Gain from ineffectiveness of cash flow hedges $ 0.0 $ 1.9 (Loss) gain from contracts not designated as hedges (3.5 ) 0.7 Net $ (3.5 ) $ 2.6 The fair value associated with forward contracts related to foreign currency that are not designated as hedges are immediately charged to earnings. These amounts are classified in cost of sales in the Condensed Consolidated Statement of Operations and Comprehensive Income. As of March 31, 2018, the Company has outstanding foreign currency forward contracts consisting of a gross derivative liability of $0.5 million (recognized in accrued liabilities in the balance sheet) and a gross derivative asset of $0.7 million (recognized in other current assets in the balance sheet). As of December 31, 2017, the Company has outstanding currency forward contracts with a net fair value totaling $0.1 million, consisting of a gross derivative liability of $0.2 million (recognized in accrued liabilities in the balance sheet) and a gross derivative asset of $0.3 million (recognized in other current assets in the balance sheet). As of March 31, 2018 and December 31, 2017, the net currency units outstanding for these contracts were: March 31, 2018 December 31, 2017 (In millions) British Pounds GBP 5.8 GBP 7.0 New Zealand Dollars NZD 15.8 NZD 15.5 United States Dollars USD 8.1 USD 12.5 Canadian Dollars CAD 2.5 CAD 2.5 Euro EUR 0.5 EUR 0.0

Commitments and Contingent Liab

Commitments and Contingent Liabilities	3 Months Ended
	Mar. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities	18. Commitments and Contingent Liabilities The Company and its subsidiaries are involved in litigation and various proceedings relating to environmental laws and regulations, toxic tort, product liability and other matters. Certain of these matters are discussed below. The ultimate resolution of these contingencies is subject to significant uncertainty and should the Company or its subsidiaries fail to prevail in any of these legal matters or should several of these legal matters be resolved against the Company or its subsidiaries in the same reporting period, these legal matters could, individually or in the aggregate, be material to the consolidated financial statements. Legal Proceedings Coal Tar Pitch Cases . Koppers Inc. is one of several defendants in lawsuits filed in two states in which the plaintiffs claim they suffered a variety of illnesses (including cancer) as a result of exposure to coal tar pitch sold by the defendants. There are 85 plaintiffs in 47 cases pending as of March 31, 2018, compared to 87 plaintiffs in 48 cases as of December 31, 2017. As of March 31, 2018, there are 46 cases pending in state court in Pennsylvania, and one case pending in state court in Tennessee. The plaintiffs in all 47 pending cases seek to recover compensatory damages. Plaintiffs in 43 of those cases also seek to recover punitive damages. The plaintiffs in the 46 cases filed in Pennsylvania seek unspecified damages in excess of the court’s minimum jurisdictional limit. The plaintiff in the Tennessee state court case seeks damages of $15.0 million. The other defendants in these lawsuits vary from case to case and include companies such as Beazer East, Inc. (“Beazer East”), Honeywell International Inc., Graftech International Holdings, Dow Chemical Company, UCAR Carbon Company, Inc., and SGL Carbon Corporation. Discovery is proceeding in these cases. No trial dates have been set in any of these cases. The Company has not provided a reserve for these lawsuits because, at this time, the Company cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. The timing of resolution of these cases cannot be reasonably determined. Although Koppers Inc. is vigorously defending these cases, an unfavorable resolution of these matters may have a material adverse effect on the Company’s business, financial condition, cash flows and results of operations. Environmental and Other Litigation Matters The Company and its subsidiaries are subject to federal, state, local and foreign laws and regulations and potential liabilities relating to the protection of the environment and human health and safety including, among other things, the cleanup of contaminated sites, the treatment, storage and disposal of wastes, the discharge of effluent into waterways, the emission of substances into the air and various health and safety matters. The Company’s subsidiaries expect to incur substantial costs for ongoing compliance with such laws and regulations. The Company’s subsidiaries may also face governmental or third-party claims, or otherwise incur costs, relating to cleanup of, or for injuries resulting from, contamination at sites associated with past and present operations. The Company accrues for environmental liabilities when a determination can be made that a liability is probable and reasonably estimable. Environmental and Other Liabilities Retained or Assumed by Others. The Company’s subsidiaries have agreements with former owners of certain of their operating locations under which the former owners retained, assumed and/or agreed to indemnify such subsidiaries against certain environmental and other liabilities. The most significant of these agreements was entered into at Koppers Inc.’s formation on December 29, 1988 (the “Acquisition”). Under the related asset purchase agreement between Koppers Inc. and Beazer East, subject to certain limitations, Beazer East retained the responsibility for and agreed to indemnify Koppers Inc. against certain liabilities, damages, losses and costs, including, with certain limited exceptions, liabilities under and costs to comply with environmental laws to the extent attributable to acts or omissions occurring prior to the Acquisition and liabilities related to products sold by Beazer East prior to the Acquisition (the “Indemnity”). Beazer Limited, the parent company of Beazer East, unconditionally guaranteed Beazer East’s performance of the Indemnity pursuant to a guarantee (the “Guarantee”). The Indemnity provides different mechanisms, subject to certain limitations, by which Beazer East is obligated to indemnify Koppers Inc. with regard to certain environmental, product and other liabilities and imposes certain conditions on Koppers Inc. before receiving such indemnification, including, in some cases, certain limitations regarding the time period as to which claims for indemnification can be brought. In July 2004, Koppers Inc. and Beazer East agreed to amend the environmental indemnification provisions of the December 29, 1988 asset purchase agreement to extend the indemnification period for pre-closing environmental liabilities through July 2019. As consideration for the amendment, Koppers Inc. paid Beazer East a total of $7.0 million and agreed to share toxic tort litigation defense costs arising from any sites acquired from Beazer East. The July 2004 amendment did not change the provisions of the Indemnity with respect to indemnification for non-environmental claims, such as product liability claims, which claims may continue to be asserted after July 2019. Qualified expenditures under the Indemnity are not subject to a monetary limit. Qualified expenditures under the Indemnity include (i) environmental cleanup liabilities required by third parties, such as investigation, remediation and closure costs, relating to pre-December 29, 1988 (“Pre-Closing”) acts or omissions of Beazer East or its predecessors; (ii) environmental claims by third parties for personal injuries, property damages and natural resources damages relating to Pre-Closing acts or omissions of Beazer East or its predecessors; (iii) punitive damages for the acts or omissions of Beazer East and its predecessors without regard to the date of the alleged conduct and (iv) product liability claims for products sold by Beazer East or its predecessors without regard to the date of the alleged conduct. If the third-party claims described in sections (i) and (ii) above are not made by July 2019, Beazer East will not be required to pay the costs arising from such claims under the Indemnity. However, with respect to any such claims which are made by July 2019, Beazer East will continue to be responsible for such claims under the Indemnity beyond July 2019. The Indemnity provides for the resolution of issues between Koppers Inc. and Beazer East by an arbitrator on an expedited basis upon the request of either party. The arbitrator could be asked, among other things, to make a determination regarding the allocation of environmental responsibilities between Koppers Inc. and Beazer East. Arbitration decisions under the Indemnity are final and binding on the parties. Contamination has been identified at most manufacturing and other sites of the Company’s subsidiaries. One site currently owned and operated by Koppers Inc. in the United States is listed on the National Priorities List promulgated under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, as amended (“CERCLA”). Currently, at the properties acquired from Beazer East (which includes the National Priorities List site and all but one of the sites permitted under the Resource Conservation and Recovery Act (“RCRA”)), a significant portion of all investigative, cleanup and closure activities are being conducted and paid for by Beazer East pursuant to the terms of the Indemnity. In addition, other of Koppers Inc.’s sites are or have been operated under RCRA and various other environmental permits, and remedial and closure activities are being conducted at some of these sites. To date, the parties that retained, assumed and/or agreed to indemnify the Company against the liabilities referred to above, including Beazer East, have performed their obligations in all material respects. The Company believes that, for the last three years ended December 31, 2017, amounts paid by Beazer East as a result of its environmental remediation obligations under the Indemnity have averaged, in total, approximately $10 million per year. Periodically, issues have arisen between Koppers Inc. and Beazer East and/or other indemnitors that have been resolved without arbitration. Koppers Inc. and Beazer East engage in discussions from time to time that involve, among other things, the allocation of environmental costs related to certain operating and closed facilities. If for any reason (including disputed coverage or financial incapability) one or more of such parties fail to perform their obligations and the Company or its subsidiaries are held liable for or otherwise required to pay all or part of such liabilities without reimbursement, the imposition of such liabilities on the Company or its subsidiaries could have a material adverse effect on its business, financial condition, cash flows and results of operations. Furthermore, the Company could be required to record a contingent liability on its balance sheet with respect to such matters, which could result in a negative impact to the Company’s business, financial condition, cash flows and results of operations. Domestic Environmental Matters. 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 March 31, 2018, 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 March 31, 2018, the Company’s estimated environmental remediation liability for these acquired sites totals $2.7 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 $3.3 million as of March 31, 2018. Environmental Reserves Rollforward. The following table reflects changes in the accrued liability for environmental matters, of which $5.7 million and $5.1 million are classified as current liabilities at March 31, 2018 and December 31, 2017, respectively: Period ended March 31, 2018 December 31, 2017 (Dollars in millions) Balance at beginning of year $ 13.9 $ 12.9 Expense 1.0 3.2 Reversal of reserves 0.0 (0.7 ) Cash expenditures (0.4 ) (1.8 ) Currency translation 0.0 0.3 Balance at end of period $ 14.5 $ 13.9

Subsidiary Guarantor Informatio

Subsidiary Guarantor Information for Koppers Inc. Shelf Registration	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Subsidiary Guarantor Information for Koppers Inc. Shelf Registration	19. Subsidiary Guarantor Information for Koppers Inc. Shelf Registration Under a registration statement on Form S-3, Koppers Holdings may sell a combination of securities, including common stock, debt securities, preferred stock, depository shares, warrants, purchase contracts and units, from time to time in one or more offerings. In addition, Koppers Inc. may sell debt securities from time to time under the registration statement. Debt securities may be fully and unconditionally guaranteed, on a joint and several basis, by Koppers Holdings, Koppers Inc., Koppers Asia LLC, Koppers World-Wide Ventures Corporation, Koppers Concrete Products, Inc., Concrete Partners, Inc., Koppers Delaware, Inc., Koppers Ventures, Inc., Koppers Performance Chemicals Inc., Koppers-Nevada Limited Liability Company, Koppers NZ LLC, Koppers Railroad Structures Inc., Wood Protection LP and Wood Management LLC. Non-guarantor subsidiaries are owned directly or indirectly by Koppers Inc. or are owned directly or indirectly by Koppers World-Wide Ventures Corporation. The guarantor subsidiaries that issue guarantees, if any, will be determined when a debt offering actually occurs under the registration statement and accordingly, the condensed consolidating financial information for subsidiary guarantors will be revised to identify the subsidiaries that actually provided guarantees. These guarantees will be governed pursuant to a 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 March 31, 2018, Koppers Inc.’s assets exceeded its liabilities by $106.4 million. The amount of restricted net assets unavailable for distribution to Koppers Holdings Inc. by Koppers Inc. totals $31.0 million as of March 31, 2018. Cash dividends paid to Koppers Holdings Inc. by its subsidiaries totaled $7.4 million and $0.3 million for the three months ended March 31, 2018 and 2017, respectively. Condensed Consolidating Statement of Operations For the Three Months Ended March 31, 2018 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 131.1 $ 77.5 $ 215.7 $ (18.2 ) $ 406.1 Cost of sales including depreciation and amortization 0.0 122.9 62.3 157.7 (18.2 ) 324.7 Selling, general and administrative 0.6 12.1 12.0 13.4 0.0 38.1 Operating profit (loss) (0.6 ) (3.9 ) 3.2 44.6 0.0 43.3 Other income 0.0 (0.4 ) 0.4 0.2 0.0 0.2 Equity income (loss) of subsidiaries 18.3 36.5 33.6 0.0 (88.4 ) 0.0 Interest expense 0.0 9.9 0.0 0.6 0.0 10.5 Income taxes (0.1 ) 4.0 0.9 4.4 0.0 9.2 Income from continuing operations 17.8 18.3 36.3 39.8 (88.4 ) 23.8 Discontinued operations 0.0 0.0 0.0 (0.1 ) 0.0 (0.1 ) Noncontrolling interests 0.0 0.0 0.0 5.9 0.0 5.9 Net income attributable to Koppers $ 17.8 $ 18.3 $ 36.3 $ 33.8 $ (88.4 ) $ 17.8 Comprehensive income attributable to Koppers $ 10.1 $ 10.6 $ 28.0 $ 34.6 $ (73.2 ) $ 10.1 Condensed Consolidating Statement of Operations For the Three Months Ended March 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 150.9 $ 81.2 $ 136.4 $ (21.9 ) $ 346.6 Cost of sales including depreciation and amortization 0.0 147.7 54.0 105.8 (19.9 ) 287.6 Selling, general and administrative 0.5 10.6 10.2 9.6 0.0 30.9 Operating profit (loss) (0.5 ) (7.4 ) 17.0 21.0 (2.0 ) 28.1 Other income (loss) 0.0 (0.6 ) 0.6 1.7 (0.2 ) 1.5 Equity income (loss) of subsidiaries 4.9 26.3 17.4 0.0 (48.6 ) 0.0 Interest expense 0.0 9.7 0.1 0.9 (0.1 ) 10.6 Loss on extinguishment of debt 0.0 13.3 0.0 0.0 0.0 13.3 Income taxes 0.0 (9.6 ) 6.5 4.1 0.0 1.0 Income (loss) from continuing operations 4.4 4.9 28.4 17.7 (50.7 ) 4.7 Discontinued operations 0.0 0.0 0.0 (0.1 ) 0.0 (0.1 ) Noncontrolling interests 0.0 0.0 0.0 0.2 0.0 0.2 Net income attributable to Koppers $ 4.4 $ 4.9 $ 28.4 $ 17.4 $ (50.7 ) $ 4.4 Comprehensive income (loss) attributable to Koppers $ 12.1 $ 12.6 $ 35.9 $ 23.5 $ (72.0 ) $ 12.1 Condensed Consolidating Balance Sheet March 31, 2018 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 $ 52.2 $ 0.0 $ 52.2 Receivables, net 0.0 60.8 33.9 119.7 0.0 214.4 Affiliated receivables 1.1 18.5 3.1 7.5 (30.2 ) 0.0 Inventories, net 0.0 85.1 43.5 116.6 (2.0 ) 243.2 Other current assets 0.0 6.2 14.5 18.8 0.4 39.9 Total current assets 1.1 170.6 95.0 314.8 (31.8 ) 549.7 Equity investments 105.7 810.6 311.2 (0.1 ) (1,227.4 ) 0.0 Property, plant and equipment, net 0.0 171.7 46.9 134.3 0.0 352.9 Goodwill 0.0 0.8 153.1 68.6 0.0 222.5 Intangible assets, net 0.0 7.0 94.1 44.0 0.0 145.1 Deferred tax assets 0.0 29.3 (10.4 ) 2.1 0.0 21.0 Affiliated loan receivables 0.0 41.2 137.0 4.6 (182.8 ) 0.0 Other assets 0.0 4.4 9.2 11.2 0.0 24.8 Total assets $ 106.8 $ 1,235.6 $ 836.1 $ 579.5 $ (1,442.0 ) $ 1,316.0 LIABILITIES AND EQUITY Accounts payable 0.1 69.5 32.8 45.6 0.0 148.0 Affiliated payables 0.0 14.5 1.5 15.1 (31.1 ) 0.0 Accrued liabilities 0.0 55.9 14.1 39.8 0.0 109.8 Current maturities of long-term debt 0.0 0.1 0.1 7.7 0.0 7.9 Total current liabilities 0.1 140.0 48.5 108.2 (31.1 ) 265.7 Long-term debt 0.0 759.7 0.2 23.0 0.0 782.9 Affiliated debt 0.0 137.4 32.8 12.6 (182.8 ) 0.0 Other long-term liabilities 0.0 92.1 14.4 42.2 0.1 148.8 Total liabilities 0.1 1,129.2 95.9 186.0 (213.8 ) 1,197.4 Koppers shareholders’ equity 106.7 106.4 740.2 381.6 (1,228.2 ) 106.7 Noncontrolling interests 0.0 0.0 0.0 11.9 0.0 11.9 Total liabilities and equity $ 106.8 $ 1,235.6 $ 836.1 $ 579.5 $ (1,442.0 ) $ 1,316.0 Condensed Consolidating Balance Sheet December 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) ASSETS Cash and cash equivalents $ 0.0 $ 0.7 $ 0.0 $ 59.6 $ 0.0 $ 60.3 Receivables, net 0.0 48.6 27.7 84.6 0.0 160.9 Affiliated receivables 0.6 19.4 (83.0 ) (12.1 ) 75.1 0.0 Inventories, net 0.0 80.4 40.5 117.9 (1.9 ) 236.9 Deferred tax assets 0.0 0.0 0.0 (0.1 ) 0.1 0.0 Other current assets 0.0 6.6 23.0 18.8 0.2 48.6 Total current assets 0.6 155.7 8.2 268.7 73.5 506.7 Equity investments 99.3 716.3 276.8 (0.1 ) (1,092.3 ) 0.0 Property, plant and equipment, net 0.0 155.2 47.3 125.5 0.0 328.0 Goodwill 0.0 0.8 153.1 34.3 0.0 188.2 Intangible assets, net 0.0 7.2 96.7 25.7 0.0 129.6 Deferred tax assets 0.0 29.4 (13.2 ) 2.2 0.0 18.4 Affiliated loan receivables 0.0 34.9 224.3 21.4 (280.6 ) 0.0 Other assets 0.0 4.4 15.3 9.6 0.0 29.3 Total assets $ 99.9 $ 1,103.9 $ 808.5 $ 487.3 $ (1,299.4 ) $ 1,200.2 LIABILITIES AND EQUITY Accounts payable $ 0.0 $ 65.1 $ 32.4 $ 44.4 $ 0.0 $ 141.9 Affiliated payables 0.0 (90.3 ) 13.8 2.2 74.3 0.0 Accrued liabilities 0.0 59.9 16.4 51.6 0.0 127.9 Current maturities of long-term debt 0.0 0.1 0.0 11.3 0.0 11.4 Total current liabilities 0.0 34.8 62.6 109.5 74.3 281.2 Long-term debt 0.0 643.3 0.0 22.3 0.0 665.6 Affiliated debt 0.0 233.7 19.3 27.6 (280.6 ) 0.0 Other long-term liabilities 0.0 92.0 14.4 41.2 0.0 147.6 Total liabilities 0.0 1,003.8 96.3 200.6 (206.3 ) 1,094.4 Koppers shareholders’ equity 99.9 100.1 712.2 280.8 (1,093.1 ) 99.9 Noncontrolling interests 0.0 0.0 0.0 5.9 0.0 5.9 Total liabilities and equity $ 99.9 $ 1,103.9 $ 808.5 $ 487.3 $ (1,299.4 ) $ 1,200.2 Condensed Consolidating Statement of Cash Flows For the Three Months Ended March 31, 2018 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ 6.1 $ (30.0 ) $ (3.5 ) $ 5.8 $ (7.4 ) $ (29.0 ) Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (82.0 ) (1.1 ) (2.3 ) 0.0 (85.4 ) Repayments (loans to) from affiliates 0.0 (0.1 ) 4.0 (0.7 ) (3.2 ) 0.0 Net cash provided by divestitures and asset sales 0.0 0.0 0.0 0.3 0.0 0.3 Net cash (used in) provided by investing activities 0.0 (82.1 ) 2.9 (2.7 ) (3.2 ) (85.1 ) Cash provided by (used in) financing activities: Borrowings (repayments) of long-term debt 0.0 116.8 0.3 (4.0 ) 0.0 113.1 Borrowings (repayments) of affiliated debt 0.0 3.1 0.3 (6.6 ) 3.2 0.0 Debt issuance costs 0.0 (1.1 ) 0.0 0.0 0.0 (1.1 ) Dividends paid 0.0 (7.4 ) 0.0 0.0 7.4 0.0 Stock repurchased (6.1 ) 0.0 0.0 0.0 0.0 (6.1 ) Net cash provided by (used in) financing activities (6.1 ) 111.4 0.6 (10.6 ) 10.6 105.9 Effect of exchange rates on cash 0.0 0.0 0.0 0.1 0.0 0.1 Net increase in cash and cash equivalents 0.0 (0.7 ) 0.0 (7.4 ) 0.0 (8.1 ) Cash and cash equivalents at beginning of year 0.0 0.7 0.0 59.6 0.0 60.3 Cash and cash equivalents at end of period $ 0.0 $ 0.0 $ 0.0 $ 52.2 $ 0.0 $ 52.2 Condensed Consolidating Statement of Cash Flows For the Three Months Ended March 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ (0.3 ) $ (26.9 ) $ 7.1 $ (3.7 ) $ (0.3 ) $ (24.1 ) Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (9.7 ) (3.7 ) (1.5 ) 0.0 (14.9 ) Repayments (loans to) from affiliates 0.0 5.6 3.0 0.4 (9.0 ) 0.0 Repayment of loan 0.0 0.0 0.0 9.5 0.0 9.5 Net cash proceeds from divestitures and asset sales 0.0 0.0 0.2 0.3 0.0 0.5 Net cash (used in) provided by investing activities 0.0 (4.1 ) (0.5 ) 8.7 (9.0 ) (4.9 ) Cash provided by (used in) financing activities: Repayments of long-term debt 0.0 43.2 0.0 (1.0 ) 0.0 42.2 Borrowings (repayments) of affiliated debt 0.0 (0.9 ) (6.6 ) (1.5 ) 9.0 0.0 Deferred financing cost 0.0 (11.0 ) 0.0 0.0 0.0 (11.0 ) Dividends paid 0.0 (0.3 ) 0.0 0.0 0.3 0.0 Stock repurchased 0.3 0.0 0.0 0.0 0.0 0.3 Net cash provided by (used in) financing activities 0.3 31.0 (6.6 ) (2.5 ) 9.3 31.5 Effect of exchange rates on cash 0.0 0.0 0.0 0.1 0.0 0.1 Net decrease in cash and cash equivalents 0.0 0.0 0.0 2.6 0.0 2.6 Cash and cash equivalents at beginning of year 0.0 0.0 0.0 20.8 0.0 20.8 Cash and cash equivalents at end of period $ 0.0 $ 0.0 $ 0.0 $ 23.4 $ 0.0 $ 23.4

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	20. Related Party Transactions During 2016, the Company sold its 30 percent interest in TKK. Refer to “Note 14 – 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	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	21. Fair Value Measurements Carrying amounts and the related estimated fair values of the Company’s financial instruments as of March 31, 2018 and December 31, 2017 are as follows: March 31, 2018 December 31, 2017 Fair Value Carrying Value Fair Value Carrying Value (Dollars in millions) Financial assets: Cash and cash equivalents, including restricted cash $ 52.2 $ 52.2 $ 60.3 $ 60.3 Investments and other assets (a) 1.1 1.1 1.1 1.1 Financial liabilities: Long-term debt (including current portion) $ 820.8 $ 803.0 $ 706.9 $ 688.7 (a) Excludes equity method investments. Cash and cash equivalents – The carrying value approximates fair value because of the short maturity of those instruments. Investments and other assets – Represents the broker-quoted cash surrender value on universal life insurance policies. This asset is classified as Level 2 in the valuation hierarchy and is measured from values received from financial institutions. Debt – The fair value of the Company’s long-term debt is estimated based on the market prices for the same or similar issues or on the current rates offered to the Company for debt of the same remaining maturities (Level 2). The fair value of the Company’s revolving credit facility approximates carrying value due to the variable rate nature of this instrument.

New Accounting Pronouncements (

New Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Changes And Error Corrections [Abstract]
New Accounting Pronouncements	In May 2014, the Financial Accounting Standards Board (“FASB”) or services. Subsequent to the issuance of ASU 2014-09, the FASB issued multiple ASUs which either amended or clarified ASU 2014-09. Collectively, the revenue recognition ASUs were effective for annual reporting periods beginning after December 15, 2017. The Company elected to use the modified retrospective method for transition in which the cumulative effect was recognized at our January 1, 2018 date of adoption with no restatement of comparative periods presented. The implementation of the guidance had no material impact on the measurement of recognition of revenue of prior periods; however, additional disclosures have been added in accordance with the ASU. In August 2017, the FASB issued ASU No. 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities.” This ASU amends and simplifies existing guidance in order to allow companies to more accurately present the economic effects of risk management activities in the financial statements. The Company adopted this ASU effective January 1, 2018 and the Company reclassified a $3.6 million unrealized gain, net of tax, from retained earnings to accumulated other comprehensive loss upon adoption. In March 2017, the FASB issued ASU 2017-07, “Compensation – Retirement Benefits (Topic 715)”, in order to improve the presentation of net periodic pension and postretirement costs. The amendment requires that an employer report the service cost component in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The amendments in this update related to income statement activity are applied. As a practical expedient, the Company has used the amounts disclosed in its pension and post-retirement benefits footnote as the estimation basis for applying the retrospective presentation requirements. The Company adopted this ASU effective January 1, 2018, and for retrospective presentation, reclassified $0.4 million In January 2017, the FASB issued ASU No. 2017-04, “Simplifying the Test for Goodwill Impairment (Topic 350).” The update is intended to simplify how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. The amendments in this update are effective for periods beginning after December 15, 2019. Entities are required to apply the amendments in this update prospectively from the date of adoption, with early adoption permitted. The Company adopted this ASU effective January 1, 2018. In August 2016, the FASB The Company adopted this ASU effective January 1, 2018 In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842).” ASU 2016-02 requires an entity to recognize a right-of-use asset and lease liability for all leases with terms of more than one year. Recognition, measurement and presentation of expenses will depend on classification as a finance or operating lease. The standard is effective January 1, 2019 and requires a modified retrospective adoption. The Company has a project team analyzing all of its leases to determine the impact of the adoption of ASU 2016-02 will have on its consolidated financial statements expected to be completed during the third quarter of 2018, but anticipates that it will result in a significant right-of-use asset and related lease liability to be recognized on our consolidated balance sheet as certain of our manufacturing facilities, offices and equipment are currently categorized as operating leases.

Plant Closures and Divestitur29

Plant Closures and Divestitures (Tables)	3 Months Ended
	Mar. 31, 2018
Discontinued Operations And Disposal Groups [Abstract]
Summary of Restructuring Activities and Related Reserves	Details of the restructuring activities and related reserves are as follows: Severance employee Environmental remediation Site demolition Other Total (Dollars in millions) Reserve at December 31, 2016 $ 1.4 $ 1.5 $ 10.0 $ 3.2 $ 16.1 Accrual 0.9 2.1 4.7 6.9 14.6 Cost charged against assets 0.0 0.0 0.0 (6.3 ) (6.3 ) Reversal of accrued charges (0.3 ) 0.0 (1.8 ) 0.0 (2.1 ) Cash paid (0.3 ) (1.1 ) (2.4 ) (1.0 ) (4.8 ) Currency translation 0.0 0.2 0.1 0.5 0.8 Reserve at December 31, 2017 $ 1.7 $ 2.7 $ 10.6 $ 3.3 $ 18.3 Accrual 0.0 0.9 0.3 1.2 2.4 Cost charged against assets 0.0 0.0 0.0 (1.1 ) (1.1 ) Cash paid 0.0 (0.2 ) (1.8 ) (0.1 ) (2.1 ) Currency translation 0.0 (0.1 ) 0.0 0.0 (0.1 ) Reserve at March 31, 2018 $ 1.7 $ 3.3 $ 9.1 $ 3.3 $ 17.4

Acquisitions (Tables)

Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
Summary of Preliminary Valuation of Identifiable Assets Acquired and Liabilities Assumed Upon Acquisition	The preliminary valuation of identifiable assets acquired and liabilities assumed upon the acquisition of MAER are shown in the table below. February 28, 2018 (Dollars in millions) Cash and cash equivalents $ 3.2 Accounts receivable 4.9 Other current assets 0.3 Property, plant and equipment 6.6 Intangibles 19.3 Goodwill 34.1 Total assets acquired 68.4 Accounts payable & accrued expenses 2.3 Net assets acquired $ 66.1

Comprehensive Income and Equi31

Comprehensive Income and Equity (Tables)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Schedule of Comprehensive Income	Total comprehensive income for the three months ended March 31, 2018 and 2017 is summarized in the table below: Three Months Ended March 31, 2018 2017 (Dollars in millions) Net income $ 23.7 $ 4.6 Other comprehensive income: Change in currency translation adjustment 1.2 6.1 Unrealized (loss) gain on cash flow hedges, net of tax benefit (expense) of $4.9 and $(0.9) (9.3 ) 1.3 Change in accounting standard 0.3 0.0 Unrecognized pension net loss, net of tax expense of $0.1 and $0.2 0.3 0.3 Total comprehensive income 16.2 12.3 Less: Comprehensive income attributable to noncontrolling interests 6.1 0.2 Comprehensive income attributable to Koppers $ 10.1 $ 12.1
Schedule of Change in Equity	The following tables present the change in equity for the three months ended March 31, 2018 and 2017, respectively: (Dollars in millions) Total Koppers Shareholders’ Equity Noncontrolling Interests Total Equity Balance at December 31, 2017 $ 99.9 $ 5.9 $ 105.8 Net income 17.8 5.9 23.7 Issuance of common stock 1.3 0.0 1.3 Employee stock plans 2.8 0.0 2.8 Other comprehensive (loss) income (7.7 ) 0.1 (7.6 ) Repurchases of common stock (7.4 ) 0.0 (7.4 ) Balance at March 31, 2018 $ 106.7 $ 11.9 $ 118.6 (Dollars in millions) Total Koppers Shareholders’ Equity Noncontrolling Interests Total Equity Balance at December 31, 2016 $ 30.4 $ 4.2 $ 34.6 Net income 4.4 0.2 4.6 Issuance of common stock 1.6 0.0 1.6 Employee stock plans 2.4 0.0 2.4 Other comprehensive income 7.7 0.0 7.7 Repurchases of common stock (1.3 ) 0.0 (1.3 ) Balance at March 31, 2017 $ 45.2 $ 4.4 $ 49.6

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Earnings per Common Share	The following table sets forth the computation of basic and diluted earnings per common share: Three Months Ended March 31, 2018 2017 (Dollars in millions, except share amounts, in thousands, and per share amounts) Net income attributable to Koppers $ 17.8 $ 4.4 Less: Loss from discontinued operations (0.1 ) (0.1 ) Income from continuing operations attributable to Koppers $ 17.9 $ 4.5 Weighted average common shares outstanding: Basic 20,894 20,722 Effect of dilutive securities 1,264 1,024 Diluted 22,158 21,746 Income per common share – continuing operations: Basic income per common share $ 0.86 $ 0.21 Diluted income per common share 0.81 0.20 Other data: Antidilutive securities excluded from computation of diluted earnings per common share 8 128

Stock-based Compensation (Table

Stock-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options And Performance Award Fair Value Assumptions	The Company calculated the fair value of stock options on the date of grant using the Black-Scholes-Merton model and the assumptions listed below: March March March 2016 Grant March 2015 Grant Grant date price per share of stock option award $ 41.60 $ 44.10 $ 18.11 $ 17.57 Expected dividend yield per share 0.00 % 0.00 % 0.00 % 3.40 % Expected life in years 5.73 5.77 5.96 5.75 Expected volatility 37.05 % 39.70 % 40.86 % 42.27 % Risk-free interest rate 2.67 % 2.13 % 1.45 % 1.73 % Grant date fair value per share of option award $ 16.38 $ 17.90 $ 7.41 $ 5.20
Summary of Performance Stock Units	The following table shows a summary of the performance stock units as of March 31, 2018: Performance Period Minimum Shares Target Shares Maximum Shares 2016 – 2018 0 256,628 513,256 2017 – 2019 0 115,098 230,196 2018 – 2020 0 123,133 246,266
Summary of Status and Activity of Non-Vested Stock Units	The following table shows a summary of the status and activity of non-vested stock units for the three months ended March 31, 2018: Restricted Stock Units Performance Stock Units Total Stock Units Weighted Grant Date Fair Value per Unit Non-vested at December 31, 2017 238,140 581,551 819,691 $ 29.14 Granted 85,346 124,262 209,608 $ 44.78 Performance share adjustment 0 204,866 204,866 $ 17.57 Vested (73,576 ) (409,732 ) (483,308 ) $ 18.64 Forfeited (3,965 ) (6,088 ) (10,053 ) $ 37.74 Non-vested at March 31, 2018 245,945 494,859 740,804 $ 37.09
Summary of Status and Activity of Stock Options	The following table shows a summary of the status and activity of stock options for the three months ended March 31, 2018: Options Weighted Exercise Price per Option Weighted Average Remaining Contractual Term (in years) Aggregate Value (in millions) Outstanding at December 31, 2017 942,537 $ 27.59 Granted 139,012 $ 41.60 Exercised (32,568 ) $ 39.41 Outstanding at March 31, 2018 1,048,981 $ 29.08 6.49 $ 13.1 Exercisable at March 31, 2018 653,320 $ 27.88 5.55 $ 8.8
Schedule of Stock-based Compensation Expense Recognized	Stock Compensation Expense Total stock-based compensation expense recognized for three months ended March 31, 2018 and 2017 is as follows: Three Months Ended March 31, 2018 2017 (Dollars in millions) Stock-based compensation expense recognized: Selling, general and administrative expenses $ 2.9 $ 2.3 Less related income tax benefit 1.0 0.9 Decrease in net income attributable to Koppers $ 1.9 $ 1.4 Intrinsic value of exercised stock options $ 0.2 $ 0.7 Cash received from the exercise of stock options $ 0.9 $ 1.6
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 March 2016 Grant Grant date price per share of performance award $ 41.60 $ 44.10 $ 18.11 Expected dividend yield per share 0.00 % 0.00 % 0.00 % Expected volatility 39.40 % 43.50 % 40.86 % Risk-free interest rate 2.35 % 1.54 % 0.96 % Look-back period in years 2.84 2.83 2.84 Grant date fair value per share of performance award $ 47.12 $ 64.02 $ 23.70

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Summary of Results of Segment Operations	The following table sets forth certain sales and operating data, net of all intersegment transactions, for the Company’s segments for the periods indicated: Three Months Ended March 31, 2018 2017 (Dollars in millions) Revenues from external customers: Railroad and Utility Products and Services $ 108.4 $ 135.5 Performance Chemicals 97.4 96.7 Carbon Materials and Chemicals 200.3 114.4 Total $ 406.1 $ 346.6 Intersegment revenues: Performance Chemicals $ 1.8 $ 1.7 Carbon Materials and Chemicals 18.2 18.9 Total $ 20.0 $ 20.6 Depreciation and amortization expense: Railroad and Utility Products and Services $ 3.0 $ 3.0 Performance Chemicals 4.4 4.4 Carbon Materials and Chemicals 4.4 3.8 Total $ 11.8 $ 11.2 Operating profit (loss): Railroad and Utility Products and Services $ 1.1 $ 9.3 Performance Chemicals 5.6 18.6 Carbon Materials and Chemicals 37.2 0.6 Corporate (a) (0.6 ) (0.4 ) Total $ 43.3 $ 28.1 (a) Operating loss for Corporate includes primarily general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc.
Schedule of Segment Revenues for Significant Product Lines	The following table sets forth revenues for significant product lines, net of all intersegment transactions, for the Company’s segments for the periods indicated: Three Months Ended March 31, 2018 2017 (Dollars in millions) Railroad and Utility Products and Services: Railroad treated products $ 79.4 $ 108.7 Utility poles 11.5 10.8 Rail joints 8.3 7.4 Railroad infrastructure services 7.0 8.6 Other products 2.2 0.0 108.4 135.5 Performance Chemicals: Wood preservative products 95.0 93.6 Other products 2.4 3.1 97.4 96.7 Carbon Materials and Chemicals: Pitch and related products 129.2 48.2 Creosote and distillates 22.9 20.5 Phthalic anhydride and other chemicals 22.2 20.3 Naphthalene 13.1 9.1 Other products 12.9 16.3 200.3 114.4 Total $ 406.1 $ 346.6
Summary of Tangible and Intangible Assets by Segments	The following table sets forth certain tangible and intangible assets allocated to each of the Company’s segments as of the dates indicated: March 31, 2018 December 31, 2017 (Dollars in millions) Segment assets: Railroad and Utility Products and Services $ 330.2 $ 249.7 Performance Chemicals 496.0 494.0 Carbon Materials and Chemicals 447.0 414.2 All other 42.8 42.3 Total $ 1,316.0 $ 1,200.2 Goodwill: Railroad and Utility Products and Services $ 44.5 $ 10.5 Performance Chemicals 178.0 177.7 Total $ 222.5 $ 188.2

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Summary of Income Taxes Reconciled with Federal Statutory Rate	The estimated annual effective income tax rate differs from the U.S. federal statutory tax rate due to: March 31, 2018 March 31, 2017 Federal income tax rate 21.0 % 35.0 % State income taxes, net of federal tax benefit 0.9 1.7 Foreign earnings taxed at different rates 3.5 (11.3 ) Valuation allowance adjustments (5.7 ) 0.0 Change in tax contingency reserves 0.1 0.2 GILTI inclusion (net of foreign tax credits) 13.1 0.0 Other 1.5 1.4 Estimated annual effective income tax rate 34.4 % 27.0 %

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Components of Inventories	Net inventories as of March 31, 2018 and December 31, 2017 are summarized in the table below: March 31, 2018 December 31, 2017 (Dollars in millions) Raw materials $ 180.1 $ 173.6 Work in process 10.9 11.2 Finished goods 100.1 98.4 $ 291.1 $ 283.2 Less revaluation to LIFO 47.9 46.3 Net $ 243.2 $ 236.9

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	3 Months Ended
	Mar. 31, 2018
Property Plant And Equipment [Abstract]
Property, Plant and Equipment	Property, plant and equipment as of March 31, 2018 and December 31, 2017 are summarized in the table below: March 31, 2018 December 31, 2017 (Dollars in millions) Land $ 17.7 $ 17.6 Buildings 64.4 63.4 Machinery and equipment 790.4 756.6 $ 872.5 $ 837.6 Less accumulated depreciation 519.6 509.6 Net $ 352.9 $ 328.0

Pensions and Post-Retirement 38

Pensions and Post-Retirement Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Components of Net Periodic Benefit Cost for Pension Plans	The following table provides the components of net periodic benefit cost for the pension plans for the three months ended March 31, 2018 and 2017: Three Months Ended March 31, 2018 2017 (Dollars in millions) Service cost $ 0.5 $ 0.5 Interest cost 1.8 2.4 Expected return on plan assets (2.1 ) (2.5 ) Amortization of net loss 0.4 0.5 Net periodic benefit cost $ 0.6 $ 0.9 Defined contribution plan expense $ 2.0 $ 2.2

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Schedule of Long-Term Debt Instruments	Debt as of March 31, 2018 and December 31, 2017 was as follows: Weighted Average Interest Rate Maturity March 31, 2018 December 31, 2017 (Dollars in millions) Revolving Credit Facility 4.34 % 2022 $ 271.9 $ 155.0 Construction and other loans 4.78 % 2020 31.1 33.7 Senior Notes due 2025 6.00 % 2025 500.0 500.0 Debt 803.0 688.7 Less short-term debt and current maturities of long-term debt 7.9 11.4 Less unamortized debt issuance costs 12.2 11.7 Long-term debt $ 782.9 $ 665.6

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	3 Months Ended
	Mar. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Changes in Carrying Values of Asset Retirement Obligations	The following table reflects changes in the carrying values of asset retirement obligations: March 31, 2018 December 31, 2017 (Dollars in millions) Asset retirement obligation at beginning of year $ 37.1 $ 36.0 Accretion expense 0.4 2.4 Revision in estimated cash flows 0.0 9.4 Cash expenditures (2.1 ) (10.9 ) Currency translation 0.1 0.2 Balance at end of period $ 35.5 $ 37.1

Deferred Revenue (Tables)

Deferred Revenue (Tables)	3 Months Ended
	Mar. 31, 2018
Deferred Revenue Disclosure [Abstract]
Deferred Revenue from Extended Product Warranty Liabilities	The following table reflects changes in the carrying values of deferred revenue: March 31, 2018 December 31, 2017 (Dollars in millions) Balance at beginning of year $ 28.1 $ 27.2 Revenue earned (0.2 ) (0.7 ) Currency translation 0.8 1.6 Balance at end of period $ 28.7 $ 28.1

Derivative Financial Instrume42

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Schedule of Outstanding Copper Swap Contracts	As of March 31, 2018 and December 31, 2017, the Company has outstanding copper swap contracts of the following amounts: Units Outstanding (in Pounds) Net Fair Value - Asset March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 (Amounts in millions) Cash flow hedges 39.8 37.8 $ 13.8 $ 25.5 Not designated as hedges 12.9 11.3 1.0 4.5 Total 52.7 49.1 $ 14.8 $ 30.0
Schedule of Fair Value of Outstanding Copper Swap Contracts Recorded in Balance Sheet	As of March 31, 2018 and December 31, 2017, the fair value of the outstanding copper swap contracts is recorded in the balance sheet as follows: March 31, 2018 December 31, 2017 (Dollars in millions) Other current assets $ 12.7 $ 21.8 Other assets 3.5 8.2 Accrued liabilities (1.4 ) 0.0 Net asset on balance sheet $ 14.8 $ 30.0 Accumulated other comprehensive gain, net of tax $ 10.5 $ 15.8
Summary of Amount Recognized in Earnings Related to Copper Swap Contracts	See Note 6 – Comprehensive Income and Equity, for amounts recorded in other comprehensive income and for amounts reclassified from accumulated other comprehensive income to net income for the periods specified below. For the three months ended March 31, 2018 and 2017, the following amounts were recognized in earnings related to copper swap contracts: Three Months Ended March 31, 2018 2017 (Dollars in millions) Gain from ineffectiveness of cash flow hedges $ 0.0 $ 1.9 (Loss) gain from contracts not designated as hedges (3.5 ) 0.7 Net $ (3.5 ) $ 2.6
Summary of Net Currency Units Outstanding	As of March 31, 2018 and December 31, 2017, the net currency units outstanding for these contracts were: March 31, 2018 December 31, 2017 (In millions) British Pounds GBP 5.8 GBP 7.0 New Zealand Dollars NZD 15.8 NZD 15.5 United States Dollars USD 8.1 USD 12.5 Canadian Dollars CAD 2.5 CAD 2.5 Euro EUR 0.5 EUR 0.0

Commitments and Contingent Li43

Commitments and Contingent Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Changes in Accrued Liability for Environmental Matters	The following table reflects changes in the accrued liability for environmental matters, of which $5.7 million and $5.1 million are classified as current liabilities at March 31, 2018 and December 31, 2017, respectively: Period ended March 31, 2018 December 31, 2017 (Dollars in millions) Balance at beginning of year $ 13.9 $ 12.9 Expense 1.0 3.2 Reversal of reserves 0.0 (0.7 ) Cash expenditures (0.4 ) (1.8 ) Currency translation 0.0 0.3 Balance at end of period $ 14.5 $ 13.9

Subsidiary Guarantor Informat44

Subsidiary Guarantor Information for Koppers Inc. Shelf Registration (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Condensed Consolidating Statement of Operations	Condensed Consolidating Statement of Operations For the Three Months Ended March 31, 2018 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 131.1 $ 77.5 $ 215.7 $ (18.2 ) $ 406.1 Cost of sales including depreciation and amortization 0.0 122.9 62.3 157.7 (18.2 ) 324.7 Selling, general and administrative 0.6 12.1 12.0 13.4 0.0 38.1 Operating profit (loss) (0.6 ) (3.9 ) 3.2 44.6 0.0 43.3 Other income 0.0 (0.4 ) 0.4 0.2 0.0 0.2 Equity income (loss) of subsidiaries 18.3 36.5 33.6 0.0 (88.4 ) 0.0 Interest expense 0.0 9.9 0.0 0.6 0.0 10.5 Income taxes (0.1 ) 4.0 0.9 4.4 0.0 9.2 Income from continuing operations 17.8 18.3 36.3 39.8 (88.4 ) 23.8 Discontinued operations 0.0 0.0 0.0 (0.1 ) 0.0 (0.1 ) Noncontrolling interests 0.0 0.0 0.0 5.9 0.0 5.9 Net income attributable to Koppers $ 17.8 $ 18.3 $ 36.3 $ 33.8 $ (88.4 ) $ 17.8 Comprehensive income attributable to Koppers $ 10.1 $ 10.6 $ 28.0 $ 34.6 $ (73.2 ) $ 10.1 Condensed Consolidating Statement of Operations For the Three Months Ended March 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Net sales $ 0.0 $ 150.9 $ 81.2 $ 136.4 $ (21.9 ) $ 346.6 Cost of sales including depreciation and amortization 0.0 147.7 54.0 105.8 (19.9 ) 287.6 Selling, general and administrative 0.5 10.6 10.2 9.6 0.0 30.9 Operating profit (loss) (0.5 ) (7.4 ) 17.0 21.0 (2.0 ) 28.1 Other income (loss) 0.0 (0.6 ) 0.6 1.7 (0.2 ) 1.5 Equity income (loss) of subsidiaries 4.9 26.3 17.4 0.0 (48.6 ) 0.0 Interest expense 0.0 9.7 0.1 0.9 (0.1 ) 10.6 Loss on extinguishment of debt 0.0 13.3 0.0 0.0 0.0 13.3 Income taxes 0.0 (9.6 ) 6.5 4.1 0.0 1.0 Income (loss) from continuing operations 4.4 4.9 28.4 17.7 (50.7 ) 4.7 Discontinued operations 0.0 0.0 0.0 (0.1 ) 0.0 (0.1 ) Noncontrolling interests 0.0 0.0 0.0 0.2 0.0 0.2 Net income attributable to Koppers $ 4.4 $ 4.9 $ 28.4 $ 17.4 $ (50.7 ) $ 4.4 Comprehensive income (loss) attributable to Koppers $ 12.1 $ 12.6 $ 35.9 $ 23.5 $ (72.0 ) $ 12.1
Condensed Consolidating Balance Sheet	Condensed Consolidating Balance Sheet March 31, 2018 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 $ 52.2 $ 0.0 $ 52.2 Receivables, net 0.0 60.8 33.9 119.7 0.0 214.4 Affiliated receivables 1.1 18.5 3.1 7.5 (30.2 ) 0.0 Inventories, net 0.0 85.1 43.5 116.6 (2.0 ) 243.2 Other current assets 0.0 6.2 14.5 18.8 0.4 39.9 Total current assets 1.1 170.6 95.0 314.8 (31.8 ) 549.7 Equity investments 105.7 810.6 311.2 (0.1 ) (1,227.4 ) 0.0 Property, plant and equipment, net 0.0 171.7 46.9 134.3 0.0 352.9 Goodwill 0.0 0.8 153.1 68.6 0.0 222.5 Intangible assets, net 0.0 7.0 94.1 44.0 0.0 145.1 Deferred tax assets 0.0 29.3 (10.4 ) 2.1 0.0 21.0 Affiliated loan receivables 0.0 41.2 137.0 4.6 (182.8 ) 0.0 Other assets 0.0 4.4 9.2 11.2 0.0 24.8 Total assets $ 106.8 $ 1,235.6 $ 836.1 $ 579.5 $ (1,442.0 ) $ 1,316.0 LIABILITIES AND EQUITY Accounts payable 0.1 69.5 32.8 45.6 0.0 148.0 Affiliated payables 0.0 14.5 1.5 15.1 (31.1 ) 0.0 Accrued liabilities 0.0 55.9 14.1 39.8 0.0 109.8 Current maturities of long-term debt 0.0 0.1 0.1 7.7 0.0 7.9 Total current liabilities 0.1 140.0 48.5 108.2 (31.1 ) 265.7 Long-term debt 0.0 759.7 0.2 23.0 0.0 782.9 Affiliated debt 0.0 137.4 32.8 12.6 (182.8 ) 0.0 Other long-term liabilities 0.0 92.1 14.4 42.2 0.1 148.8 Total liabilities 0.1 1,129.2 95.9 186.0 (213.8 ) 1,197.4 Koppers shareholders’ equity 106.7 106.4 740.2 381.6 (1,228.2 ) 106.7 Noncontrolling interests 0.0 0.0 0.0 11.9 0.0 11.9 Total liabilities and equity $ 106.8 $ 1,235.6 $ 836.1 $ 579.5 $ (1,442.0 ) $ 1,316.0 Condensed Consolidating Balance Sheet December 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) ASSETS Cash and cash equivalents $ 0.0 $ 0.7 $ 0.0 $ 59.6 $ 0.0 $ 60.3 Receivables, net 0.0 48.6 27.7 84.6 0.0 160.9 Affiliated receivables 0.6 19.4 (83.0 ) (12.1 ) 75.1 0.0 Inventories, net 0.0 80.4 40.5 117.9 (1.9 ) 236.9 Deferred tax assets 0.0 0.0 0.0 (0.1 ) 0.1 0.0 Other current assets 0.0 6.6 23.0 18.8 0.2 48.6 Total current assets 0.6 155.7 8.2 268.7 73.5 506.7 Equity investments 99.3 716.3 276.8 (0.1 ) (1,092.3 ) 0.0 Property, plant and equipment, net 0.0 155.2 47.3 125.5 0.0 328.0 Goodwill 0.0 0.8 153.1 34.3 0.0 188.2 Intangible assets, net 0.0 7.2 96.7 25.7 0.0 129.6 Deferred tax assets 0.0 29.4 (13.2 ) 2.2 0.0 18.4 Affiliated loan receivables 0.0 34.9 224.3 21.4 (280.6 ) 0.0 Other assets 0.0 4.4 15.3 9.6 0.0 29.3 Total assets $ 99.9 $ 1,103.9 $ 808.5 $ 487.3 $ (1,299.4 ) $ 1,200.2 LIABILITIES AND EQUITY Accounts payable $ 0.0 $ 65.1 $ 32.4 $ 44.4 $ 0.0 $ 141.9 Affiliated payables 0.0 (90.3 ) 13.8 2.2 74.3 0.0 Accrued liabilities 0.0 59.9 16.4 51.6 0.0 127.9 Current maturities of long-term debt 0.0 0.1 0.0 11.3 0.0 11.4 Total current liabilities 0.0 34.8 62.6 109.5 74.3 281.2 Long-term debt 0.0 643.3 0.0 22.3 0.0 665.6 Affiliated debt 0.0 233.7 19.3 27.6 (280.6 ) 0.0 Other long-term liabilities 0.0 92.0 14.4 41.2 0.0 147.6 Total liabilities 0.0 1,003.8 96.3 200.6 (206.3 ) 1,094.4 Koppers shareholders’ equity 99.9 100.1 712.2 280.8 (1,093.1 ) 99.9 Noncontrolling interests 0.0 0.0 0.0 5.9 0.0 5.9 Total liabilities and equity $ 99.9 $ 1,103.9 $ 808.5 $ 487.3 $ (1,299.4 ) $ 1,200.2
Condensed Consolidating Statement of Cash Flows	Condensed Consolidating Statement of Cash Flows For the Three Months Ended March 31, 2018 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ 6.1 $ (30.0 ) $ (3.5 ) $ 5.8 $ (7.4 ) $ (29.0 ) Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (82.0 ) (1.1 ) (2.3 ) 0.0 (85.4 ) Repayments (loans to) from affiliates 0.0 (0.1 ) 4.0 (0.7 ) (3.2 ) 0.0 Net cash provided by divestitures and asset sales 0.0 0.0 0.0 0.3 0.0 0.3 Net cash (used in) provided by investing activities 0.0 (82.1 ) 2.9 (2.7 ) (3.2 ) (85.1 ) Cash provided by (used in) financing activities: Borrowings (repayments) of long-term debt 0.0 116.8 0.3 (4.0 ) 0.0 113.1 Borrowings (repayments) of affiliated debt 0.0 3.1 0.3 (6.6 ) 3.2 0.0 Debt issuance costs 0.0 (1.1 ) 0.0 0.0 0.0 (1.1 ) Dividends paid 0.0 (7.4 ) 0.0 0.0 7.4 0.0 Stock repurchased (6.1 ) 0.0 0.0 0.0 0.0 (6.1 ) Net cash provided by (used in) financing activities (6.1 ) 111.4 0.6 (10.6 ) 10.6 105.9 Effect of exchange rates on cash 0.0 0.0 0.0 0.1 0.0 0.1 Net increase in cash and cash equivalents 0.0 (0.7 ) 0.0 (7.4 ) 0.0 (8.1 ) Cash and cash equivalents at beginning of year 0.0 0.7 0.0 59.6 0.0 60.3 Cash and cash equivalents at end of period $ 0.0 $ 0.0 $ 0.0 $ 52.2 $ 0.0 $ 52.2 Condensed Consolidating Statement of Cash Flows For the Three Months Ended March 31, 2017 Parent Koppers Inc. Domestic Guarantor Subsidiaries Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated (Dollars in millions) Cash provided by (used in) operating activities $ (0.3 ) $ (26.9 ) $ 7.1 $ (3.7 ) $ (0.3 ) $ (24.1 ) Cash provided by (used in) investing activities: Capital expenditures and acquisitions 0.0 (9.7 ) (3.7 ) (1.5 ) 0.0 (14.9 ) Repayments (loans to) from affiliates 0.0 5.6 3.0 0.4 (9.0 ) 0.0 Repayment of loan 0.0 0.0 0.0 9.5 0.0 9.5 Net cash proceeds from divestitures and asset sales 0.0 0.0 0.2 0.3 0.0 0.5 Net cash (used in) provided by investing activities 0.0 (4.1 ) (0.5 ) 8.7 (9.0 ) (4.9 ) Cash provided by (used in) financing activities: Repayments of long-term debt 0.0 43.2 0.0 (1.0 ) 0.0 42.2 Borrowings (repayments) of affiliated debt 0.0 (0.9 ) (6.6 ) (1.5 ) 9.0 0.0 Deferred financing cost 0.0 (11.0 ) 0.0 0.0 0.0 (11.0 ) Dividends paid 0.0 (0.3 ) 0.0 0.0 0.3 0.0 Stock repurchased 0.3 0.0 0.0 0.0 0.0 0.3 Net cash provided by (used in) financing activities 0.3 31.0 (6.6 ) (2.5 ) 9.3 31.5 Effect of exchange rates on cash 0.0 0.0 0.0 0.1 0.0 0.1 Net decrease in cash and cash equivalents 0.0 0.0 0.0 2.6 0.0 2.6 Cash and cash equivalents at beginning of year 0.0 0.0 0.0 20.8 0.0 20.8 Cash and cash equivalents at end of period $ 0.0 $ 0.0 $ 0.0 $ 23.4 $ 0.0 $ 23.4

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Company's Financial Instruments	Carrying amounts and the related estimated fair values of the Company’s financial instruments as of March 31, 2018 and December 31, 2017 are as follows: March 31, 2018 December 31, 2017 Fair Value Carrying Value Fair Value Carrying Value (Dollars in millions) Financial assets: Cash and cash equivalents, including restricted cash $ 52.2 $ 52.2 $ 60.3 $ 60.3 Investments and other assets (a) 1.1 1.1 1.1 1.1 Financial liabilities: Long-term debt (including current portion) $ 820.8 $ 803.0 $ 706.9 $ 688.7 (a) Excludes equity method investments.

New Accounting Pronouncements -

New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Cost of goods sold	$ (311.4)	$ (274.9)
Selling, general and administrative expenses	(38.1)	(30.9)
ASU No. 2017-12 [Member]
Summary Of Significant Accounting Policies [Line Items]
Reclassification of unrealized gain from retained earnings to accumulated other comprehensive loss	$ 3.6
ASU No. 2017-07 [Member] | Scenario, Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Cost of goods sold		0.4
Selling, general and administrative expenses		$ 0.1

Plant Closures and Divestitur47

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

Plant Closures and Divestitur48

Plant Closures and Divestitures - Summary of Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	$ 18.3	$ 16.1
Accrual	2.4	14.6
Cost charged against assets	(1.1)	(6.3)
Reversal of accrued charges		(2.1)
Cash paid	(2.1)	(4.8)
Currency translation	(0.1)	0.8
Reserve, Ending Balance	17.4	18.3
Severance and Employee Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	1.7	1.4
Accrual	0	0.9
Cost charged against assets	0	0
Reversal of accrued charges		(0.3)
Cash paid	0	(0.3)
Currency translation	0	0
Reserve, Ending Balance	1.7	1.7
Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	2.7	1.5
Accrual	0.9	2.1
Cost charged against assets	0	0
Reversal of accrued charges		0
Cash paid	(0.2)	(1.1)
Currency translation	(0.1)	0.2
Reserve, Ending Balance	3.3	2.7
Site Demolition [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	10.6	10
Accrual	0.3	4.7
Cost charged against assets	0	0
Reversal of accrued charges		(1.8)
Cash paid	(1.8)	(2.4)
Currency translation	0	0.1
Reserve, Ending Balance	9.1	10.6
Other [Member]
Restructuring Cost and Reserve [Line Items]
Reserve, Beginning Balance	3.3	3.2
Accrual	1.2	6.9
Cost charged against assets	(1.1)	(6.3)
Reversal of accrued charges		0
Cash paid	(0.1)	(1)
Currency translation	0	0.5
Reserve, Ending Balance	$ 3.3	$ 3.3

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) $ in Millions	Apr. 10, 2018USD ($)FacilityYard	Feb. 28, 2018USD ($)Facility	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Goodwill			$ 222.5	$ 188.2
M.A. Energy Resources, LLC [Member]
Business Acquisition [Line Items]
Cash consideration		$ 66.1
Number of processing facilities | Facility		3
Revenues				$ 30
Goodwill		$ 34.1
Intangibles assets		19.3
Acquisition expenses			$ 2.1
M.A. Energy Resources, LLC [Member] | Railroad and Utility Products and Services [Member]
Business Acquisition [Line Items]
Goodwill		34.1
M.A. Energy Resources, LLC [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangibles assets		$ 18.7
Intangibles assets, amortized period		12 years
M.A. Energy Resources, LLC [Member] | Trade Name [Member]
Business Acquisition [Line Items]
Intangibles assets		$ 0.6
Intangibles assets, amortized period		2 years
Cox Industries, Inc. [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Cash consideration	$ 200
Number of manufacturing facilities | Facility	8
Number of distribution yards | Yard	19

Acquisitions - Summary of Preli

Acquisitions - Summary of Preliminary Valuation of Identifiable Assets Acquired and Liabilities Assumed Upon Acquisition (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Feb. 28, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 222.5		$ 188.2
M.A. Energy Resources, LLC [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		$ 3.2
Accounts receivable		4.9
Other current assets		0.3
Property, plant and equipment		6.6
Intangibles		19.3
Goodwill		34.1
Total assets acquired		68.4
Accounts payable & accrued expenses		2.3
Net assets acquired		$ 66.1

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Disaggregation Of Revenue [Line Items]
Cost of sales (excluding items below)	$ 311.4	$ 274.9
Accounting Standards Update 2014-09 [Member]
Disaggregation Of Revenue [Line Items]
Cumulative increase to opening balance of retained earnings				$ 0.3
Impact of restatement on revenue not previously recognized				$ 5.3
Effect on revenue	4
Accounting Standards Update 2014-09 [Member] | Accounts Receivable, Net
Disaggregation Of Revenue [Line Items]
Contract assets	18.7		$ 5.3
Accounting Standards Update 2014-09 [Member] | Impact of Changes in Accounting Policies, Effect of Change [Member] | RUPS [Member]
Disaggregation Of Revenue [Line Items]
Effect on revenue	1.3
Cost of sales (excluding items below)	$ 1.2

Comprehensive Income and Equi52

Comprehensive Income and Equity - Schedule of Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Net income	$ 23.7	$ 4.6
Other comprehensive income:
Change in currency translation adjustment	1.2	6.1
Unrealized (loss) gain on cash flow hedges, net of tax benefit (expense) of $4.9 and $(0.9)	(9.3)	1.3
Change in accounting standard	0.3	0
Unrecognized pension net loss, net of tax expense of $0.1 and $0.2	0.3	0.3
Total comprehensive income	16.2	12.3
Less: Comprehensive income attributable to noncontrolling interests	6.1	0.2
Comprehensive income attributable to Koppers	$ 10.1	$ 12.1

Comprehensive Income and Equi53

Comprehensive Income and Equity - Schedule of Comprehensive Income (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Tax (benefit) expense, unrealized gains on cash flow hedges	$ 4.9	$ (0.9)
Tax expense, unrecognized pension net income	$ 0.1	$ 0.2

Comprehensive Income and Equi54

Comprehensive Income and Equity - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Income related to derivative instrument	$ 2.5	$ 1.3

Comprehensive Income and Equi55

Comprehensive Income and Equity - Schedule of Change in Equity (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	$ 105.8	$ 34.6
Net income	23.7	4.6
Issuance of common stock	1.3	1.6
Employee stock plans	2.8	2.4
Other comprehensive (loss) income	(7.6)	7.7
Repurchases of common stock	(7.4)	(1.3)
Balance	118.6	49.6
Total Koppers Shareholders' Equity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	99.9	30.4
Net income	17.8	4.4
Issuance of common stock	1.3	1.6
Employee stock plans	2.8	2.4
Other comprehensive (loss) income	(7.7)	7.7
Repurchases of common stock	(7.4)	(1.3)
Balance	106.7	45.2
Noncontrolling Interests [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	5.9	4.2
Net income	5.9	0.2
Issuance of common stock	0	0
Employee stock plans	0	0
Other comprehensive (loss) income	0.1	0
Repurchases of common stock	0	0
Balance	$ 11.9	$ 4.4

Earnings per Common Share - Sch

Earnings per Common Share - Schedule of Computation of Basic and Diluted Earnings per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to Koppers	$ 17.8	$ 4.4
Less: Loss from discontinued operations	(0.1)	(0.1)
Income from continuing operations attributable to Koppers	$ 17.9	$ 4.5
Weighted average common shares outstanding:
Basic	20,894	20,722
Effect of dilutive securities	1,264	1,024
Diluted	22,158	21,746
Income per common share – continuing operations:
Basic income per common share	$ 0.86	$ 0.21
Diluted income per common share	$ 0.81	$ 0.20
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share	8	128

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future gross compensation expense related to non-vested stock-based compensation arrangements, which are expected to vest	$ 23.7
Future compensation expense, weighted-average expected period of recognition in months	30 months
Restricted Stock Units (RSUs) [Member] | Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	1 year
Restricted Stock Units (RSUs) [Member] | Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	4 years
Restricted Stock Units (RSUs) [Member] | Employee [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	2 years
Performance Stock Units [Member] | March 2016 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period		3 years
Vesting performance stock units if minimum performance criteria are not achieved		0
Stock options, term in years		3 years
Vesting Percentage	200.00%
Performance Stock Units [Member] | March 2016 and Thereafter Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	3 years
Vesting performance stock units if minimum performance criteria are not achieved	0
Stock options, term in years	3 years
Performance Stock Units [Member] | Maximum [Member] | March 2016 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants		200.00%
Performance Stock Units [Member] | Maximum [Member] | March 2016 and Thereafter Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants	200.00%
Performance Stock Units [Member] | Minimum [Member] | March 2016 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants		0.00%
Performance Stock Units [Member] | Minimum [Member] | March 2016 and Thereafter Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants	0.00%
Employee Stock Option [Member] | Grants in March 2015 and Thereafter [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, term in years	10 years
Employee Stock Option [Member] | Executive Officer | Grants in March 2015 and Thereafter [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	4 years

Stock-based Compensation - Perf

Stock-based Compensation - Performance Award Fair Value Assumptions (Detail)	3 Months Ended
	Mar. 31, 2018$ / shares
March 2018 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 41.60
Expected dividend yield per share	0.00%
Expected volatility	37.05%
Risk-free interest rate	2.67%
Grant date fair value per share	$ 16.38
March 2018 Grant [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 41.60
Expected dividend yield per share	0.00%
Expected volatility	39.40%
Risk-free interest rate	2.35%
Look-back period in years	2 years 10 months 2 days
Grant date fair value per share	$ 47.12
March 2017 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 44.10
Expected dividend yield per share	0.00%
Expected volatility	39.70%
Risk-free interest rate	2.13%
Grant date fair value per share	$ 17.90
March 2017 Grant [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 44.10
Expected dividend yield per share	0.00%
Expected volatility	43.50%
Risk-free interest rate	1.54%
Look-back period in years	2 years 9 months 29 days
Grant date fair value per share	$ 64.02
March 2016 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 18.11
Expected dividend yield per share	0.00%
Expected volatility	40.86%
Risk-free interest rate	1.45%
Grant date fair value per share	$ 7.41
March 2016 Grant [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 18.11
Expected dividend yield per share	0.00%
Expected volatility	40.86%
Risk-free interest rate	0.96%
Look-back period in years	2 years 10 months 2 days
Grant date fair value per share	$ 23.70

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Performance Stock Units (Detail) - shares	Mar. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	740,804	819,691
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	494,859	581,551
Minimum [Member] | 2016 - 2018 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	0
Minimum [Member] | 2017 - 2019 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	0
Minimum [Member] | 2018 - 2020 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	0
Target Shares [Member] | 2016 - 2018 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	256,628
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	115,098
Target Shares [Member] | 2018 - 2020 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	123,133
Maximum [Member] | 2016 - 2018 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	513,256
Maximum [Member] | 2017 - 2019 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	230,196
Maximum [Member] | 2018 - 2020 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	246,266

Stock-based Compensation - Su60

Stock-based Compensation - Summary of Status and Activity of Non-Vested Stock Units (Detail)	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	819,691
Granted	209,608
Performance share adjustment	204,866
Vested	(483,308)
Forfeited	(10,053)
Non-vested, Ending Balance	740,804
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit | $ / shares	$ 29.14
Granted, Weighted Average Grant Date Fair Value per Unit | $ / shares	44.78
Performance share adjustment | $ / shares	17.57
Vested, Weighted Average Grant Date Fair Value per Unit | $ / shares	18.64
Forfeited, Weighted Average Grant Date Fair Value per Unit | $ / shares	37.74
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit | $ / shares	$ 37.09
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	238,140
Granted	85,346
Performance share adjustment	0
Vested	(73,576)
Forfeited	(3,965)
Non-vested, Ending Balance	245,945
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	581,551
Granted	124,262
Performance share adjustment	204,866
Vested	(409,732)
Forfeited	(6,088)
Non-vested, Ending Balance	494,859

Stock-based Compensation - Stoc

Stock-based Compensation - Stock Options Fair Value Assumptions (Detail)	3 Months Ended
	Mar. 31, 2018$ / shares
March 2018 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 41.60
Expected dividend yield per share	0.00%
Expected life in years	5 years 8 months 23 days
Expected volatility	37.05%
Risk-free interest rate	2.67%
Grant date fair value per share	$ 16.38
March 2017 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 44.10
Expected dividend yield per share	0.00%
Expected life in years	5 years 9 months 7 days
Expected volatility	39.70%
Risk-free interest rate	2.13%
Grant date fair value per share	$ 17.90
March 2016 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 18.11
Expected dividend yield per share	0.00%
Expected life in years	5 years 11 months 15 days
Expected volatility	40.86%
Risk-free interest rate	1.45%
Grant date fair value per share	$ 7.41
March 2015 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share	$ 17.57
Expected dividend yield per share	3.40%
Expected life in years	5 years 9 months
Expected volatility	42.27%
Risk-free interest rate	1.73%
Grant date fair value per share	$ 5.20

Stock-based Compensation - Su62

Stock-based Compensation - Summary of Status and Activity of Stock Options (Detail) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options, Outstanding at December 31, 2017 | shares	942,537
Options, Granted | shares	139,012
Options, Exercised | shares	(32,568)
Options, Outstanding at March 30, 2018 | shares	1,048,981
Options, Exercisable at March 30, 2018 | shares	653,320
Weighted Average Exercise Price per Option, Outstanding at December 31, 2017 | $ / shares	$ 27.59
Weighted Average Exercise Price per Option, Granted | $ / shares	41.60
Weighted Average Exercise Price per Option, Exercised | $ / shares	39.41
Weighted Average Exercise Price per Option, Outstanding at March 30, 2018 | $ / shares	29.08
Weighted Average Exercise Price per Option, Exercisable at March 30, 2018 | $ / shares	$ 27.88
Weighted Average Remaining Contractual Term, Outstanding at March 30, 2018	6 years 5 months 26 days
Weighted Average Remaining Contractual Term, Exercisable at March 30, 2018	5 years 6 months 18 days
Aggregate Intrinsic Value, Outstanding at March 30, 2018 | $	$ 13.1
Aggregate Intrinsic Value, Exercisable at March 30, 2018 | $	$ 8.8

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock-based compensation expense recognized:
Less related income tax benefit	$ 1	$ 0.9
Decrease in net income attributable to Koppers	1.9	1.4
Intrinsic value of exercised stock options	0.2	0.7
Cash received from the exercise of stock options	0.9	1.6
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense recognized:
Stock-based compensation expense	$ 2.9	$ 2.3

Segment Information - Additiona

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018Segment
Segment Reporting [Abstract]
Number of reportable segments	3

Segment Information - Summary o

Segment Information - Summary of Results of Segment Operations (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Revenues from external customers:
Net sales		$ 406.1	$ 346.6
Depreciation and amortization expense		11.8	11.2
Operating profit (loss)	[1]	43.3	28.1
Railroad and Utility Products and Services [Member]
Revenues from external customers:
Net sales		108.4	135.5
Performance Chemicals [Member]
Revenues from external customers:
Net sales		97.4	96.7
Carbon Materials and Chemicals [Member]
Revenues from external customers:
Net sales		200.3	114.4
Operating Segments [Member] | Railroad and Utility Products and Services [Member]
Revenues from external customers:
Net sales		108.4	135.5
Depreciation and amortization expense		3	3
Operating profit (loss)		1.1	9.3
Operating Segments [Member] | Performance Chemicals [Member]
Revenues from external customers:
Net sales		97.4	96.7
Depreciation and amortization expense		4.4	4.4
Operating profit (loss)		5.6	18.6
Operating Segments [Member] | Carbon Materials and Chemicals [Member]
Revenues from external customers:
Net sales		200.3	114.4
Depreciation and amortization expense		4.4	3.8
Operating profit (loss)		37.2	0.6
Intersegment [Member]
Revenues from external customers:
Net sales		20	20.6
Intersegment [Member] | Performance Chemicals [Member]
Revenues from external customers:
Net sales		1.8	1.7
Intersegment [Member] | Carbon Materials and Chemicals [Member]
Revenues from external customers:
Net sales		18.2	18.9
Corporate, Non-Segment [Member]
Revenues from external customers:
Operating profit (loss)		$ (0.6)	$ (0.4)
[1]	Operating loss for Corporate includes primarily general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc.

Segment Information - Schedule

Segment Information - Schedule of Segment Revenues for Significant Product Lines (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 406.1	$ 346.6
Railroad and Utility Products and Services [Member]
Segment Reporting Information [Line Items]
Net sales	108.4	135.5
Railroad and Utility Products and Services [Member] | Railroad Treated Products [Member]
Segment Reporting Information [Line Items]
Net sales	79.4	108.7
Railroad and Utility Products and Services [Member] | Utility Poles [Member]
Segment Reporting Information [Line Items]
Net sales	11.5	10.8
Railroad and Utility Products and Services [Member] | Rail Joints [Member]
Segment Reporting Information [Line Items]
Net sales	8.3	7.4
Railroad and Utility Products and Services [Member] | Railroad Infrastructure Services [Member]
Segment Reporting Information [Line Items]
Net sales	7	8.6
Railroad and Utility Products and Services [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	2.2	0
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	97.4	96.7
Performance Chemicals [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	2.4	3.1
Performance Chemicals [Member] | Wood Preservative Products [Member]
Segment Reporting Information [Line Items]
Net sales	95	93.6
Carbon Materials and Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	200.3	114.4
Carbon Materials and Chemicals [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	12.9	16.3
Carbon Materials and Chemicals [Member] | Pitch and Related Products [Member]
Segment Reporting Information [Line Items]
Net sales	129.2	48.2
Carbon Materials and Chemicals [Member] | Phthalic Anhydride and Other Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	22.2	20.3
Carbon Materials and Chemicals [Member] | Creosote and Distillates [Member]
Segment Reporting Information [Line Items]
Net sales	22.9	20.5
Carbon Materials and Chemicals [Member] | Naphthalene [Member]
Segment Reporting Information [Line Items]
Net sales	$ 13.1	$ 9.1

Segment Information - Summary67

Segment Information - Summary of Tangible and Intangible Assets by Segments (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 1,316	$ 1,200.2
Goodwill	222.5	188.2
Railroad and Utility Products and Services [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	330.2	249.7
Goodwill	44.5	10.5
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	496	494
Goodwill	178	177.7
Carbon Materials and Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	447	414.2
All Other [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 42.8	$ 42.3

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Taxes [Line Items]
Corporate income tax rate	21.00%	35.00%
Provisional charge recorded to income tax expense related to one-time transition tax on unrepatriated foreign earnings			$ 13,100,000
Domestic losses and other tax credits resulting in estimated cash payment	$ 4,700,000
Provisional charge recorded to income tax expense related to corporate income tax rate reduction	$ 0
Estimated annual effective income tax rate	34.40%	27.00%
Income taxes as a percentage of pretax income	27.90%	17.50%
Net tax benefit included in income taxes, discrete items	$ 2,200,000	$ 400,000
Excess tax benefits from stock based compensation		800,000
Additional accruals for uncertain tax positions		$ 400,000
Unrecognized tax benefits with impact on the effective tax rate	4,500,000		4,400,000
Unrecognized tax benefits	8,800,000		8,700,000
Accrued interest expense and penalties	3,800,000		$ 3,600,000
Decrease in unrecognized tax benefits	$ 4,000,000
Maximum [Member]
Income Taxes [Line Items]
One-time transition tax expected payment in installments period	8 years

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Taxes Reconciled with Federal Statutory Rate (Detail)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Federal income tax rate	21.00%	35.00%
State income taxes, net of federal tax benefit	0.90%	1.70%
Foreign earnings taxed at different rates	3.50%	(11.30%)
Valuation allowance adjustments	(5.70%)	0.00%
Change in tax contingency reserves	0.10%	0.20%
GILTI inclusion (net of foreign tax credits)	13.10%	0.00%
Other	1.50%	1.40%
Estimated annual effective income tax rate	34.40%	27.00%

Inventories - Components of Net

Inventories - Components of Net Inventories (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 180.1	$ 173.6
Work in process	10.9	11.2
Finished goods	100.1	98.4
Inventories, gross	291.1	283.2
Less revaluation to LIFO	47.9	46.3
Net	$ 243.2	$ 236.9

Property, Plant and Equipment -

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 872.5	$ 837.6
Less accumulated depreciation	519.6	509.6
Net	352.9	328
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	17.7	17.6
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	64.4	63.4
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 790.4	$ 756.6

Property, Plant and Equipment72

Property, Plant and Equipment - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property Plant And Equipment [Abstract]
Impairment charges	$ 0	$ 0

Pensions and Post-Retirement 73

Pensions and Post-Retirement Benefit Plans - Additional Information (Detail)	Mar. 31, 2018Plan
Defined Benefit Plan Disclosure [Line Items]
Number of domestic non-qualified defined benefit plans	3
Salaried and Hourly Employees [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of domestic non-qualified defined benefit plans	2

Pensions and Post-Retirement 74

Pensions and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Postemployment Benefits [Abstract]
Service cost	$ 0.5	$ 0.5
Interest cost	1.8	2.4
Expected return on plan assets	(2.1)	(2.5)
Amortization of net loss	0.4	0.5
Net periodic benefit cost	0.6	0.9
Defined contribution plan expense	$ 2	$ 2.2

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt Instruments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Debt	$ 803	$ 688.7
Less short-term debt and current maturities of long-term debt	7.9	11.4
Less unamortized debt issuance costs	12.2	11.7
Long-term debt	$ 782.9	665.6
Senior Secured Credit Facilities [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.34%
Debt, Maturity	2,022
Debt	$ 271.9	155
Committed Loan Facility Agreements [Member] | Construction Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.78%
Debt, Maturity	2,020
Debt	$ 31.1	33.7
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
Debt	$ 500	$ 500

Debt - Additional Information (

Debt - Additional Information (Detail) ¥ in Millions	Feb. 15, 2022	Apr. 10, 2018USD ($)	Feb. 28, 2017USD ($)	Mar. 31, 2018USD ($)Installment	Mar. 31, 2017USD ($)	Mar. 31, 2018CNY (¥)Installment	Feb. 26, 2018USD ($)
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ 10,000,000	$ 0	$ 13,300,000
Bond premium and bond tender expenses			7,300,000
Write-off unamortized debt issuance cost			2,700,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility			$ 400,000,000				$ 600,000,000
Revolving credit facility, maturity period			2022-02
Revolving credit facility, variable interest rate basis			LIBOR
Write-off unamortized debt issuance cost			$ 3,300,000
Revolving Credit Facility [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Revolving credit facility		$ 600,000,000
Revolving credit facility, variable interest rate basis		LIBOR
Revolving credit facility, extended maturity period		1 year
Revolving credit facility, extended maturity date		2023-02
Initial average borrowing rate		5.00%
Secured Term Loan Facility [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Secured term loan		$ 100,000,000
Quarterly amortization		$ 2,500,000
Secured term loan maturity period		5 years
Initial average borrowing rate		5.00%
6.00 percent Senior Notes due 2025 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
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				$ 35,400,000
Senior Secured Credit Facilities [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, unused borrowing capacity				$ 268,100,000
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%

Asset Retirement Obligations -

Asset Retirement Obligations - Schedule of Changes in Carrying Values of Asset Retirement Obligations (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]
Asset retirement obligation at beginning of year	$ 37.1	$ 36
Accretion expense	0.4	2.4
Revision in estimated cash flows	0	9.4
Cash expenditures	(2.1)	(10.9)
Currency translation	0.1	0.2
Balance at end of period	$ 35.5	$ 37.1

Deferred Revenue - Summary of C

Deferred Revenue - Summary of Changes in Carrying Values of Deferred Revenue (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Deferred Revenue Disclosure [Abstract]
Deferred revenue at beginning of year	$ 28.1	$ 27.2
Revenue earned	(0.2)	(0.7)
Currency translation	0.8	1.6
Deferred revenue at end of year	$ 28.7	$ 28.1

Deferred Revenue - Additional I

Deferred Revenue - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Deferred Revenue Disclosure [Abstract]
Deferred revenue	$ 27.9	$ 27.2

Derivative Financial Instrume80

Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Maximum period hedged in cash flow hedge	36 months
Unrealized gains, reclassification period	12 months
Unrealized gains, net of tax, expected to be reclassified from other comprehensive income into earnings	$ 7.7
Forward Contracts [Member]
Derivative [Line Items]
Not designated net fair value - asset (liability)		$ 0.1
Accrued Liabilities [Member] | Forward Contracts [Member]
Derivative [Line Items]
Not designated gross derivative liability	0.5	0.2
Other Current Assets [Member] | Forward Contracts [Member]
Derivative [Line Items]
Not designated gross derivative assets	$ 0.7	$ 0.3

Derivative Financial Instrume81

Derivative Financial Instruments - Schedule of Outstanding Copper Swap Contracts (Detail) - Copper Swap Contracts [Member] £ in Millions, $ in Millions	Mar. 31, 2018USD ($)	Mar. 31, 2018GBP (£)	Dec. 31, 2017USD ($)	Dec. 31, 2017GBP (£)
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding | £		£ 52.7		£ 49.1
Net Fair Value - Asset | $	$ 14.8		$ 30
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding | £		39.8		37.8
Net Fair Value - Asset | $	13.8		25.5
Not Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding | £		£ 12.9		£ 11.3
Net Fair Value - Asset | $	$ 1		$ 4.5

Derivative Financial Instrume82

Derivative Financial Instruments - Schedule of Fair Value of Outstanding Copper Swap Contracts Recorded in Balance Sheet (Detail) - Copper Swap Contracts [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Net Fair Value - Asset	$ 14.8	$ 30
Accumulated other comprehensive gain, net of tax	10.5	15.8
Other Current Assets [Member]
Derivative [Line Items]
Net Fair Value - Asset	12.7	21.8
Other Assets [Member]
Derivative [Line Items]
Net Fair Value - Asset	3.5	8.2
Accrued Liabilities [Member]
Derivative [Line Items]
Net Fair Value - Asset	$ (1.4)	$ 0

Derivative Financial Instrume83

Derivative Financial Instruments - Schedule of Amounts Recognized In Earnings Related To Copper Swap Contracts (Detail) - Copper Swap Contracts [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
(Loss) gain from contracts not designated as hedges	$ (3.5)	$ 0.7
Net	(3.5)	2.6
Cash Flow Hedging [Member]
Derivative [Line Items]
Gain from ineffectiveness of cash flow hedges	$ 0	$ 1.9

Derivative Financial Instrume84

Derivative Financial Instruments - Summary of Net Currency Units Outstanding (Detail)	Mar. 31, 2018USD ($)	Mar. 31, 2018GBP (£)	Mar. 31, 2018NZD ($)	Mar. 31, 2018CAD ($)	Mar. 31, 2018EUR (€)	Dec. 31, 2017USD ($)	Dec. 31, 2017GBP (£)	Dec. 31, 2017NZD ($)	Dec. 31, 2017CAD ($)	Dec. 31, 2017EUR (€)
Offsetting [Abstract]
Net currency units outstanding	$ 8,100,000	£ 5,800,000	$ 15,800,000	$ 2,500,000	€ 500,000	$ 12,500,000	£ 7,000,000	$ 15,500,000	$ 2,500,000	€ 0

Commitments and Contingent Li85

Commitments and Contingent Liabilities - Additional Information (Detail)	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2004USD ($)	Mar. 31, 2018USD ($)StatePlaintiffCasesitePartyPlant	Dec. 31, 2017USD ($)PlaintiffCase	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Number of states with new claims filed | State		2
Number of plaintiffs | Plaintiff		85	87
Environmental remediation and regulation liability		$ 14,500,000	$ 13,900,000	$ 12,900,000
Accrued liability for environmental matters, current		5,700,000	$ 5,100,000
Portland Harbor and Newark Bay CERCLA sites [Member]
Loss Contingencies [Line Items]
Costs of participating in PRP group		$ 2,100,000
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		47
Punitive Damages [Member]
Loss Contingencies [Line Items]
Number of cases | Case		43
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		47	48
Reserve for legal proceedings		$ 0
Pennsylvania [Member]
Loss Contingencies [Line Items]
Number of cases | Case		46
Pennsylvania [Member] | Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases | Case		46
Tennessee [Member] | Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases | Case		1
Compensatory damages		$ 15,000,000
Oregon [Member] | Portland Harbor CERCLA site [Member]
Loss Contingencies [Line Items]
Number of potential responsible parties | Party		80
Net present value of selected remedy estimation		$ 1,100,000,000
Undiscounted cost of selected remedy estimation		1,700,000,000
United States [Member] | Performance Chemicals [Member]
Loss Contingencies [Line Items]
Environmental remediation and regulation liability		$ 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		$ 2,700,000
Number of plant sites | Plant		2
Australia [Member] | Continental Carbon facility [Member]
Loss Contingencies [Line Items]
Environmental remediation and regulation liability		$ 3,300,000

Commitments and Contingent Li86

Commitments and Contingent Liabilities - Changes in Accrued Liability for Environmental Matters (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Balance at beginning of year	$ 13.9	$ 12.9
Expense	1	3.2
Reversal of reserves	0	(0.7)
Cash expenditures	(0.4)	(1.8)
Currency translation	0	0.3
Balance at end of period	$ 14.5	$ 13.9

Subsidiary Guarantor Informat87

Subsidiary Guarantor Information for Koppers Inc. Shelf Registration - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Koppers Inc. [Member]
Debt Instrument [Line Items]
Amount of restricted net assets unavailable for distribution	$ 31
Domestic Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Cash dividends paid	7.4	$ 0.3
Senior Notes [Member] | Koppers Inc. [Member]
Debt Instrument [Line Items]
Amount of assets exceeded liabilities	$ 106.4

Subsidiary Guarantor Informat88

Subsidiary Guarantor Information for Koppers Inc. Shelf Registration - Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Millions		1 Months Ended	3 Months Ended
		Feb. 28, 2017	Mar. 31, 2018	Mar. 31, 2017
Condensed Statement Of Income Captions [Line Items]
Net sales			$ 406.1	$ 346.6
Cost of sales including depreciation and amortization			324.7	287.6
Selling, general and administrative			38.1	30.9
Operating profit	[1]		43.3	28.1
Other income (loss)			0.2	1.5
Equity income (loss) of subsidiaries			0	0
Interest expense			10.5	10.6
Loss on extinguishment of debt		$ 10	0	13.3
Income taxes			9.2	1
Income from continuing operations			23.8	4.7
Discontinued operations			(0.1)	(0.1)
Noncontrolling interests			5.9	0.2
Net income attributable to Koppers			17.8	4.4
Comprehensive income (loss) attributable to Koppers			10.1	12.1
Consolidation Eliminations [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales			(18.2)	(21.9)
Cost of sales including depreciation and amortization			(18.2)	(19.9)
Selling, general and administrative			0	0
Operating profit			0	(2)
Other income (loss)			0	(0.2)
Equity income (loss) of subsidiaries			(88.4)	(48.6)
Interest expense			0	(0.1)
Loss on extinguishment of debt				0
Income taxes			0	0
Income from continuing operations			(88.4)	(50.7)
Discontinued operations			0	0
Noncontrolling interests			0	0
Net income attributable to Koppers			(88.4)	(50.7)
Comprehensive income (loss) attributable to Koppers			(73.2)	(72)
Parent [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales			0	0
Cost of sales including depreciation and amortization			0	0
Selling, general and administrative			0.6	0.5
Operating profit			(0.6)	(0.5)
Other income (loss)			0	0
Equity income (loss) of subsidiaries			18.3	4.9
Interest expense			0	0
Loss on extinguishment of debt				0
Income taxes			(0.1)	0
Income from continuing operations			17.8	4.4
Discontinued operations			0	0
Noncontrolling interests			0	0
Net income attributable to Koppers			17.8	4.4
Comprehensive income (loss) attributable to Koppers			10.1	12.1
Koppers Inc. [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales			131.1	150.9
Cost of sales including depreciation and amortization			122.9	147.7
Selling, general and administrative			12.1	10.6
Operating profit			(3.9)	(7.4)
Other income (loss)			(0.4)	(0.6)
Equity income (loss) of subsidiaries			36.5	26.3
Interest expense			9.9	9.7
Loss on extinguishment of debt				13.3
Income taxes			4	(9.6)
Income from continuing operations			18.3	4.9
Discontinued operations			0	0
Noncontrolling interests			0	0
Net income attributable to Koppers			18.3	4.9
Comprehensive income (loss) attributable to Koppers			10.6	12.6
Domestic Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales			77.5	81.2
Cost of sales including depreciation and amortization			62.3	54
Selling, general and administrative			12	10.2
Operating profit			3.2	17
Other income (loss)			0.4	0.6
Equity income (loss) of subsidiaries			33.6	17.4
Interest expense			0	0.1
Loss on extinguishment of debt				0
Income taxes			0.9	6.5
Income from continuing operations			36.3	28.4
Discontinued operations			0	0
Noncontrolling interests			0	0
Net income attributable to Koppers			36.3	28.4
Comprehensive income (loss) attributable to Koppers			28	35.9
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Statement Of Income Captions [Line Items]
Net sales			215.7	136.4
Cost of sales including depreciation and amortization			157.7	105.8
Selling, general and administrative			13.4	9.6
Operating profit			44.6	21
Other income (loss)			0.2	1.7
Equity income (loss) of subsidiaries			0	0
Interest expense			0.6	0.9
Loss on extinguishment of debt				0
Income taxes			4.4	4.1
Income from continuing operations			39.8	17.7
Discontinued operations			(0.1)	(0.1)
Noncontrolling interests			5.9	0.2
Net income attributable to Koppers			33.8	17.4
Comprehensive income (loss) attributable to Koppers			$ 34.6	$ 23.5
[1]	Operating loss for Corporate includes primarily general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc.

Subsidiary Guarantor Informat89

Subsidiary Guarantor Information for Koppers Inc. Shelf Registration - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 52.2	$ 60.3	$ 23.4	$ 20.8
Receivables, net	214.4	160.9
Affiliated receivables	0	0
Inventories, net	243.2	236.9
Deferred tax assets		0
Other current assets	39.9	48.6
Total current assets	549.7	506.7
Equity investments	0	0
Property, plant and equipment, net	352.9	328
Goodwill	222.5	188.2
Intangible assets, net	145.1	129.6
Deferred tax assets	21	18.4
Affiliated loan receivables	0	0
Other assets	24.8	29.3
Total assets	1,316	1,200.2
LIABILITIES AND EQUITY
Accounts payable	148	141.9
Affiliated payables	0	0
Accrued liabilities	109.8	127.9
Current maturities of long-term debt	7.9	11.4
Total current liabilities	265.7	281.2
Long-term debt	782.9	665.6
Affiliated debt	0	0
Other long-term liabilities	148.8	147.6
Total liabilities	1,197.4	1,094.4
Koppers shareholders’ equity	106.7	99.9
Noncontrolling interests	11.9	5.9
Total liabilities and equity	1,316	1,200.2
Consolidation Eliminations [Member]
Assets
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0
Affiliated receivables	(30.2)	75.1
Inventories, net	(2)	(1.9)
Deferred tax assets		0.1
Other current assets	0.4	0.2
Total current assets	(31.8)	73.5
Equity investments	(1,227.4)	(1,092.3)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Deferred tax assets	0	0
Affiliated loan receivables	(182.8)	(280.6)
Other assets	0	0
Total assets	(1,442)	(1,299.4)
LIABILITIES AND EQUITY
Accounts payable	0	0
Affiliated payables	(31.1)	74.3
Accrued liabilities	0	0
Current maturities of long-term debt	0	0
Total current liabilities	(31.1)	74.3
Long-term debt	0	0
Affiliated debt	(182.8)	(280.6)
Other long-term liabilities	0.1	0
Total liabilities	(213.8)	(206.3)
Koppers shareholders’ equity	(1,228.2)	(1,093.1)
Noncontrolling interests	0	0
Total liabilities and equity	(1,442)	(1,299.4)
Parent [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0
Affiliated receivables	1.1	0.6
Inventories, net	0	0
Deferred tax assets		0
Other current assets	0	0
Total current assets	1.1	0.6
Equity investments	105.7	99.3
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	106.8	99.9
LIABILITIES AND EQUITY
Accounts payable	0.1	0
Affiliated payables	0	0
Accrued liabilities	0	0
Current maturities of long-term debt	0	0
Total current liabilities	0.1	0
Long-term debt	0	0
Affiliated debt	0	0
Other long-term liabilities	0	0
Total liabilities	0.1	0
Koppers shareholders’ equity	106.7	99.9
Noncontrolling interests	0	0
Total liabilities and equity	106.8	99.9
Koppers Inc. [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0	0.7	0	0
Receivables, net	60.8	48.6
Affiliated receivables	18.5	19.4
Inventories, net	85.1	80.4
Deferred tax assets		0
Other current assets	6.2	6.6
Total current assets	170.6	155.7
Equity investments	810.6	716.3
Property, plant and equipment, net	171.7	155.2
Goodwill	0.8	0.8
Intangible assets, net	7	7.2
Deferred tax assets	29.3	29.4
Affiliated loan receivables	41.2	34.9
Other assets	4.4	4.4
Total assets	1,235.6	1,103.9
LIABILITIES AND EQUITY
Accounts payable	69.5	65.1
Affiliated payables	14.5	(90.3)
Accrued liabilities	55.9	59.9
Current maturities of long-term debt	0.1	0.1
Total current liabilities	140	34.8
Long-term debt	759.7	643.3
Affiliated debt	137.4	233.7
Other long-term liabilities	92.1	92
Total liabilities	1,129.2	1,003.8
Koppers shareholders’ equity	106.4	100.1
Noncontrolling interests	0	0
Total liabilities and equity	1,235.6	1,103.9
Domestic Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0	0	0	0
Receivables, net	33.9	27.7
Affiliated receivables	3.1	(83)
Inventories, net	43.5	40.5
Deferred tax assets		0
Other current assets	14.5	23
Total current assets	95	8.2
Equity investments	311.2	276.8
Property, plant and equipment, net	46.9	47.3
Goodwill	153.1	153.1
Intangible assets, net	94.1	96.7
Deferred tax assets	(10.4)	(13.2)
Affiliated loan receivables	137	224.3
Other assets	9.2	15.3
Total assets	836.1	808.5
LIABILITIES AND EQUITY
Accounts payable	32.8	32.4
Affiliated payables	1.5	13.8
Accrued liabilities	14.1	16.4
Current maturities of long-term debt	0.1	0
Total current liabilities	48.5	62.6
Long-term debt	0.2	0
Affiliated debt	32.8	19.3
Other long-term liabilities	14.4	14.4
Total liabilities	95.9	96.3
Koppers shareholders’ equity	740.2	712.2
Noncontrolling interests	0	0
Total liabilities and equity	836.1	808.5
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	52.2	59.6	$ 23.4	$ 20.8
Receivables, net	119.7	84.6
Affiliated receivables	7.5	(12.1)
Inventories, net	116.6	117.9
Deferred tax assets		(0.1)
Other current assets	18.8	18.8
Total current assets	314.8	268.7
Equity investments	(0.1)	(0.1)
Property, plant and equipment, net	134.3	125.5
Goodwill	68.6	34.3
Intangible assets, net	44	25.7
Deferred tax assets	2.1	2.2
Affiliated loan receivables	4.6	21.4
Other assets	11.2	9.6
Total assets	579.5	487.3
LIABILITIES AND EQUITY
Accounts payable	45.6	44.4
Affiliated payables	15.1	2.2
Accrued liabilities	39.8	51.6
Current maturities of long-term debt	7.7	11.3
Total current liabilities	108.2	109.5
Long-term debt	23	22.3
Affiliated debt	12.6	27.6
Other long-term liabilities	42.2	41.2
Total liabilities	186	200.6
Koppers shareholders’ equity	381.6	280.8
Noncontrolling interests	11.9	5.9
Total liabilities and equity	$ 579.5	$ 487.3

Subsidiary Guarantor Informat90

Subsidiary Guarantor Information for Koppers Inc. Shelf Registration - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	$ (29)	$ (24.1)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(85.4)	(14.9)
Repayments (loans to) from affiliates	0	0
Repayment of loan	0	9.5
Net cash proceeds from divestitures and asset sales	0.3	0.5
Net cash used in investing activities	(85.1)	(4.9)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	113.1	42.2
Borrowings (repayments) of affiliated debt	0	0
Deferred financing cost		(11)
Payment of debt issuance costs	(1.1)	(11)
Dividends paid	0	0
Stock repurchased	(6.1)	0.3
Net cash (used in) provided by financing activities	105.9	31.5
Effect of exchange rates on cash	0.1	0.1
Net (decrease) increase in cash and cash equivalents	(8.1)	2.6
Cash and cash equivalents at beginning of period	60.3	20.8
Cash and cash equivalents at end of period	52.2	23.4
Consolidation Eliminations [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	(7.4)	(0.3)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0
Repayments (loans to) from affiliates	(3.2)	(9)
Repayment of loan		0
Net cash proceeds from divestitures and asset sales	0	0
Net cash used in investing activities	(3.2)	(9)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	0	0
Borrowings (repayments) of affiliated debt	3.2	9
Deferred financing cost		0
Payment of debt issuance costs	0
Dividends paid	7.4	0.3
Stock repurchased	0	0
Net cash (used in) provided by financing activities	10.6	9.3
Effect of exchange rates on cash	0	0
Net (decrease) increase in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Parent [Member] | Reportable Legal Entities [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	6.1	(0.3)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0
Repayments (loans to) from affiliates	0	0
Repayment of loan		0
Net cash proceeds from divestitures and asset sales	0	0
Net cash used in investing activities	0	0
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	0	0
Borrowings (repayments) of affiliated debt	0	0
Deferred financing cost		0
Payment of debt issuance costs	0
Dividends paid	0	0
Stock repurchased	(6.1)	0.3
Net cash (used in) provided by financing activities	(6.1)	0.3
Effect of exchange rates on cash	0	0
Net (decrease) increase in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Koppers Inc. [Member] | Reportable Legal Entities [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	(30)	(26.9)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(82)	(9.7)
Repayments (loans to) from affiliates	(0.1)	5.6
Repayment of loan		0
Net cash proceeds from divestitures and asset sales	0	0
Net cash used in investing activities	(82.1)	(4.1)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	116.8	43.2
Borrowings (repayments) of affiliated debt	3.1	(0.9)
Deferred financing cost		(11)
Payment of debt issuance costs	(1.1)
Dividends paid	(7.4)	(0.3)
Stock repurchased	0	0
Net cash (used in) provided by financing activities	111.4	31
Effect of exchange rates on cash	0	0
Net (decrease) increase in cash and cash equivalents	(0.7)	0
Cash and cash equivalents at beginning of period	0.7	0
Cash and cash equivalents at end of period	0	0
Domestic Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	(3.5)	7.1
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(1.1)	(3.7)
Repayments (loans to) from affiliates	4	3
Repayment of loan		0
Net cash proceeds from divestitures and asset sales	0	0.2
Net cash used in investing activities	2.9	(0.5)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	0.3	0
Borrowings (repayments) of affiliated debt	0.3	(6.6)
Deferred financing cost		0
Payment of debt issuance costs	0
Dividends paid	0	0
Stock repurchased	0	0
Net cash (used in) provided by financing activities	0.6	(6.6)
Effect of exchange rates on cash	0	0
Net (decrease) increase in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	5.8	(3.7)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(2.3)	(1.5)
Repayments (loans to) from affiliates	(0.7)	0.4
Repayment of loan		9.5
Net cash proceeds from divestitures and asset sales	0.3	0.3
Net cash used in investing activities	(2.7)	8.7
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	(4)	(1)
Borrowings (repayments) of affiliated debt	(6.6)	(1.5)
Deferred financing cost		0
Payment of debt issuance costs	0
Dividends paid	0	0
Stock repurchased	0	0
Net cash (used in) provided by financing activities	(10.6)	(2.5)
Effect of exchange rates on cash	0.1	0.1
Net (decrease) increase in cash and cash equivalents	(7.4)	2.6
Cash and cash equivalents at beginning of period	59.6	20.8
Cash and cash equivalents at end of period	$ 52.2	$ 23.4

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016
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		Mar. 31, 2018	Dec. 31, 2017
Fair Value [Member]
Financial assets:
Cash and cash equivalents, including restricted cash		$ 52.2	$ 60.3
Investments and other assets	[1]	1.1	1.1
Financial liabilities:
Long-term debt (including current portion)		820.8	706.9
Carrying Value [Member]
Financial assets:
Cash and cash equivalents, including restricted cash		52.2	60.3
Investments and other assets	[1]	1.1	1.1
Financial liabilities:
Long-term debt (including current portion)		$ 803	$ 688.7
[1]	Excludes equity method investments.