Koppers (KOP) 10-Q 7 May 14 2014 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2014	Apr. 30, 2014
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Entity Registrant Name	'Koppers Holdings Inc.	'
Entity Central Index Key	'0001315257	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	20,453,942

Condensed_Consolidated_Stateme

Condensed Consolidated Statement of Comprehensive Income (USD $)	3 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Income Statement [Abstract]	'	'
Net sales	$331.40	$370.40
Cost of sales (excluding items below)	285.1	320.5
Depreciation and amortization	8.9	7.3
Impairment and restructuring charges	15.5	0
Selling, general and administrative expenses	21.4	17.7
Operating profit	0.5	24.9
Other income	0.2	0.5
Interest expense	6.8	6.9
(Loss) income before income taxes	-6.1	18.5
Income taxes	-6	7.1
(Loss) income from continuing operations	-0.1	11.4
Income from discontinued operations, net of tax expense of $0.0 and $0.1	0	0.1
Net (loss) income	-0.1	11.5
Net (loss) income attributable to noncontrolling interests	-2.3	0.5
Net income attributable to Koppers	2.2	11
Basic -	'	'
Continuing operations	$0.11	$0.53
Discontinued operations	$0	$0
Earnings per basic common share	$0.11	$0.53
Diluted -	'	'
Continuing operations	$0.11	$0.53
Discontinued operations	$0	$0
Earnings per diluted common share	$0.11	$0.53
Comprehensive income	2.6	9.8
Comprehensive (loss) income attributable to noncontrolling interests	-2.7	0.5
Comprehensive income attributable to Koppers	$5.30	$9.30
Weighted average shares outstanding (in thousands):	'	'
Basic	20,384	20,667
Diluted	20,588	20,925
Dividends declared per common share	$0.25	$0.25

Condensed_Consolidated_Stateme1

Condensed Consolidated Statement of Comprehensive Income (Parenthetical) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Income Statement [Abstract]	'	'
Income from discontinued operations, tax expense	$0	$0.10

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheet (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Assets	'	'
Cash and cash equivalents	$54.70	$82.20
Accounts receivable, net of allowance of $3.6 and $3.6	157.3	157.9
Income tax receivable	11.1	9
Inventories, net	193.2	168.8
Deferred tax assets	12.4	10
Loan to related party	9.5	9.5
Other current assets	31.4	35.7
Total current assets	469.6	473.1
Equity in non-consolidated investments	6.7	6.6
Property, plant and equipment, net	202.5	197
Goodwill	75	72.7
Deferred tax assets	14.7	9.3
Other assets	32.7	26.2
Total assets	801.2	784.9
Liabilities	'	'
Accounts payable	91.8	107.6
Accrued liabilities	83.4	82.4
Dividends payable	5.1	5.1
Total current liabilities	180.3	195.1
Long-term debt	340	303.1
Accrued postretirement benefits	37.2	41.6
Deferred tax liabilities	15.2	14.7
Other long-term liabilities	42.1	40.6
Total liabilities	614.8	595.1
Commitments and contingent liabilities (Note 17)	'	'
Equity	'	'
Senior Convertible Preferred Stock, $0.01 par value per share; 10,000,000 shares authorized; no shares issued	0	0
Common Stock, $0.01 par value per share; 40,000,000 shares authorized; 21,897,190 and 21,722,492 shares issued	0.2	0.2
Additional paid-in capital	160.1	158.9
Retained earnings	68.3	71.3
Accumulated other comprehensive loss	-7	-10.2
Treasury stock, at cost, 1,443,248 and 1,390,494 shares	-52.4	-50.4
Total Koppers shareholders' equity	169.2	169.8
Noncontrolling interests	17.2	20
Total equity	186.4	189.8
Total liabilities and equity	$801.20	$784.90

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheet (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, except Share data, unless otherwise specified
Statement Of Financial Position [Abstract]	'	'
Accounts receivable, allowance	$3.60	$3.60
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	40,000,000	40,000,000
Common Stock, shares issued	21,897,190	21,722,492
Treasury stock, shares	1,443,248	1,390,494

Condensed_Consolidated_Stateme2

Condensed Consolidated Statement of Cash Flows (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Cash provided by (used in) operating activities:	'	'
Net (loss) income	($0.10)	$11.50
Adjustments to reconcile net cash provided by operating activities:	'	'
Depreciation and amortization	8.9	7.3
Impairment charges	4.7	0
Deferred income taxes	-7.2	0.7
Equity income, net of dividends received	0	-0.2
Change in other liabilities	-2.8	-3.6
Non-cash interest expense	0.4	0.4
Stock-based compensation	1.2	1.4
Other	0.2	0.1
(Increase) decrease in working capital:	'	'
Accounts receivable	2.1	-12.7
Inventories	-6.6	1.9
Accounts payable	-16.8	-2.5
Accrued liabilities and other working capital	2.3	1.4
Net cash provided by (used in) operating activities	-13.7	5.7
Cash provided by (used in) investing activities:	'	'
Capital expenditures	-14.8	-6.4
Acquisitions	-29.6	0
Net cash proceeds from divestitures and asset sales	0	0.2
Net cash provided by (used in) investing activities	-44.4	-6.2
Cash provided by (used in) financing activities:	'	'
Borrowings of revolving credit	67.5	36.5
Repayments of revolving credit	-52.5	-36.5
Borrowings of long-term debt	22.2	0
Issuances of Common Stock	0	0.2
Repurchases of Common Stock	-2	-1.6
Payment of deferred financing costs	0	-1.1
Dividends paid	-5	-5
Net cash provided by (used in) financing activities	30.2	-7.5
Effect of exchange rate changes on cash	0.4	-2
Net decrease in cash and cash equivalents	-27.5	-10
Cash and cash equivalents at beginning of year	82.2	66.7
Cash and cash equivalents at end of period	$54.70	$56.70

Basis_of_Presentation_and_New_

Basis of Presentation and New Accounting Standards	3 Months Ended
	Mar. 31, 2014
Accounting Policies [Abstract]	'
Basis of Presentation and New Accounting Standards	'
	1. Basis of Presentation and New Accounting Standards
	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, 2013 has been summarized from the audited balance sheet contained in the Annual Report on Form 10-K for the year ended December 31, 2013.
	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, 2013.

Dividends

Dividends	3 Months Ended
	Mar. 31, 2014
Text Block [Abstract]	'
Dividends	'
	2. Dividends
	On May 2, 2014, the Company’s board of directors declared a quarterly dividend of 25 cents per common share, payable on July 7, 2014 to shareholders of record as of May 19, 2014.

Plant_Closures_and_Discontinue

Plant Closures and Discontinued Operations	3 Months Ended
	Mar. 31, 2014
Discontinued Operations And Disposal Groups [Abstract]	'
Plant Closures and Discontinued Operations	'
	3. Plant Closures and Discontinued Operations
	On January 22, 2014, the Company announced its decision to discontinue coal tar distillation activities at its facility located in Uithoorn, the Netherlands. The decision was made as a result of a detailed analysis of its overall European manufacturing asset footprint in light of deteriorating market conditions in Europe and a variety of other factors, including regulatory requirements for significant capital expenditures at the facility. The Company is ramping down production at the Uithoorn facility over the first six months of 2014 as it transitions production to other Company-owned European facilities. The Company expects to discontinue distillation activities by mid-2014 and to complete closure at the site by the end of 2015. For the three months ended March 31, 2014, the Company recorded closure costs of $10.8 million for severance and site demolition liabilities. In the fourth quarter of 2013, the Company recorded an asset impairment charge of $6.9 million related to the facility.
	In December 2011, the Company ceased manufacturing operations at its carbon black facility located in Kurnell, Australia. This decision was made as a result of deteriorating business conditions including raw material availability and cost, competition in the export markets due to the strength of the Australian dollar and a variety of other factors. The Company estimates that total future closure costs related to this facility will be approximately $0.3 million. The closure is expected to be completed during 2015. The facility is part of the Carbon Materials and Chemicals segment. Operating profit from this discontinued operation totaled $0.0 million and $0.2 million for the three months ended March 31, 2014 and 2013, respectively.
	Details of the restructuring activities and related reserves are as follows:
		Severance and			Environmental			Site			Other			Total
		employee benefits			remediation			demolition
	(Dollars in millions)
	Reserve at December 31, 2012	$	0.2		$	6.7		$	6.3		$	0.1		$	13.3
	Reversal of accrued charges		(0.1	)		0			(0.3	)		0			(0.4	)
	Cash paid		0			(0.1	)		(2.0	)		(0.1	)		(2.2	)
	Currency translation		0			(1.0	)		(0.7	)		0			(1.7	)
	Reserve at December 31, 2013	$	0.1		$	5.6		$	3.3		$	0		$	9
	Accrual		10			0			0.8			0			10.8
	Cash paid		(0.2	)		0			0			0			(0.2	)
	Currency translation		0.1			0.2			0.2			0			0.5
	Reserve at March 31, 2014	$	10		$	5.8		$	4.3		$	0		$	20.1

Business_Acquisitions

Business Acquisitions	3 Months Ended
	Mar. 31, 2014
Business Combinations [Abstract]	'
Business Acquisitions	'
	4. Business Acquisitions
	Koppers Ashcroft – On January 20, 2014, the Company acquired the crosstie treating business and related manufacturing facility of Tolko Industries Ltd. located in Ashcroft, British Columbia, Canada. The purchase price was $29.6 million, subject to post-closing adjustments, and was funded primarily by available cash. The preliminary allocation of purchase price to acquired assets primarily consisted of inventory totaling $16.0 million, plant and equipment totaling $3.6 million, intangible assets consisting primarily of customer relationships totaling $7.4 million and Canadian tax deductible goodwill of $1.6 million. The goodwill is allocated to the Railroad and Utility Products and Services segment and the customer contracts will be amortized over a period of 12 years.
	Subsequent event – On April 13, 2014, Koppers Inc. signed an agreement to acquire the wood preservation and railroad services businesses of Osmose Holdings, Inc. (Osmose). Osmose’s wood preservation business develops, manufactures and sells wood preservation chemicals and wood treatment technologies for infrastructure, residential and commercial construction, and agricultural markets. The wood preservation business has operations and sales in North America, South America, Europe, and Australasia. Osmose’s railroad services business is a provider of railroad infrastructure services, including bridge inspection, engineering, maintenance and repair, and construction services for the Class I and shortline railroads in North America. Revenues for the acquired businesses in 2013 were approximately $390 million.
	The base purchase price is $460 million and is subject to certain closing adjustments. The base purchase price includes the value of an anticipated 338(h)(10) tax election that is expected to provide cash tax savings over the next 15 years. Koppers plans to finance the purchase through new and existing bank debt, including a new term loan and an increase to the Company’s existing revolving credit facility. The transaction is expected to close in the third quarter of 2014, subject to regulatory filings and customary closing conditions.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	5. Fair Value Measurements
	Carrying amounts and the related estimated fair values of the Company’s financial instruments as of March 31, 2014 and December 31, 2013 are as follows:
			March 31, 2014				December 31, 2013
			Fair Value		Carrying		Fair Value		Carrying
					Value				Value
	(Dollars in millions)
	Financial assets:
	Cash and cash equivalents, including restricted cash		$	54.7	$	54.7	$	82.2	$	82.2
	Investments and other assets(a)			1.4		1.4		1.4		1.4
	Financial liabilities:
	Long-term debt (including current portion)		$	365.1	$	340	$	331.2	$	303.1
	(a)	Excludes equity method investments.
	Cash and cash equivalents – The carrying amount 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 values of the revolving credit facility and construction loans approximate carrying value due to the variable rate nature of these instruments.

Comprehensive_Income_and_Equit

Comprehensive Income and Equity	3 Months Ended
	Mar. 31, 2014
Equity [Abstract]	'
Comprehensive Income and Equity	'
	6. Comprehensive Income and Equity
	Total comprehensive income for the three months ended March 31, 2014 and 2013 is summarized in the table below:
		Three Months Ended March 31,
		2014			2013
	(Dollars in millions)
	Net (loss) income	$	(0.1	)	$	11.5
	Other comprehensive income (loss):
	Change in currency translation adjustment		(0.3	)		(3.5	)
	Change in foreign currency transactions of long-term subsidiary investments		2.4			0.7
	Change in unrecognized pension net loss, net of tax expense of $0.2 and $0.6		0.6			1
	Change in unrecognized prior service cost, net of tax expense of $0.0 and $0.0		0			0.1
	Total comprehensive income		2.6			9.8
	Less: comprehensive (loss) income attributable to noncontrolling interests		(2.7	)		0.5
	Comprehensive income attributable to Koppers	$	5.3		$	9.3
	Amounts reclassified from accumulated other comprehensive income to net income consist of amounts shown for changes in unrecognized pension net loss, unrecognized prior service cost and unrecognized transition asset. These components of accumulated other comprehensive income are included in the computation of net periodic pension cost as disclosed in Note 13 – Pensions and Postretirement Benefit Plans.
	The following tables present the change in equity for the three months ended March 31, 2014 and 2013, respectively:
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity
	Balance at December 31, 2013	$	169.8		$	20		$	189.8
	Net income (loss)		2.2			(2.3	)		(0.1	)
	Employee stock plans		1.2			0			1.2
	Other comprehensive income (loss)		3.2			(0.5	)		2.7
	Dividends		(5.2	)		0			(5.2	)
	Repurchases of common stock		(2.0	)		0			(2.0	)
	Balance at March 31, 2014	$	169.2		$	17.2		$	186.4
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity’
	Balance at December 31, 2012	$	150.6		$	17.5		$	168.1
	Net income		11			0.5			11.5
	Issuance of common stock		0.2			0			0.2
	Employee stock plans		1.6			0			1.6
	Other comprehensive income		(1.7	)		0			(1.7	)
	Dividends		(5.4	)		0			(5.4	)
	Repurchases of common stock		(1.6	)		0			(1.6	)
	Balance at March 31, 2013	$	154.7		$	18		$	172.7

Earnings_per_Common_Share

Earnings per Common Share	3 Months Ended
	Mar. 31, 2014
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 earnings per common share.
	The following table sets forth the computation of basic and diluted earnings per common share:
		Three Months Ended March 31,
		2014		2013
	(Dollars in millions, except share amounts, in thousands, and per share amounts)
	Net income attributable to Koppers	$	2.2	$	11
	Less: Income from discontinued operations		0		0.1
	Income from continuing operations attributable to Koppers	$	2.2	$	10.9
	Weighted average common shares outstanding:
	Basic		20,384		20,667
	Effect of dilutive securities		204		258
	Diluted		20,588		20,925
	Earnings per common share – continuing operations:
	Basic earnings per common share	$	0.11	$	0.53
	Diluted earnings per common share		0.11		0.53
	Other data:
	Antidilutive securities excluded from computation of diluted earnings per common share		235		181

Stockbased_Compensation

Stock-based Compensation	3 Months Ended
	Mar. 31, 2014
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.
	Under the LTIP, the board of directors granted restricted stock units and performance stock units to certain employee participants (collectively, the “stock units”) each year starting in 2007. The restricted stock units vest on the third anniversary of the grant date or ratably over three years, assuming continued employment by the participant. Performance stock units granted in 2011 have a two-year performance objective. Performance stock units granted after 2011 have three-year performance objectives. Regardless of whether the measurement period for the applicable performance objective is two or three years, all performance stock units have a three-year period for vesting (if the applicable performance objective is obtained). The applicable performance objective is based upon a multi-year cumulative value creation calculation 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 150 percent of the target award based upon actual performance. If minimum performance criteria are not achieved, no performance stock units will vest.
	Dividends declared on the Company’s common stock during the restriction period 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 for most participants. There are special vesting provisions for the stock units related to a change in control.
	Restricted stock units that vest immediately or 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 members of management in connection with employee compensation.
	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 stock units is the market price of the underlying common stock on the date of grant.
	The following table shows a summary of the performance stock units as of March 31, 2014:
	Performance Period	Minimum			Target			Maximum
		Shares			Shares			Shares
	2012 – 2014		0			92,847			139,271
	2013 – 2015		0			90,661			135,992
	2014 – 2016		0			108,506			162,759
	The following table shows a summary of the status and activity of non-vested stock awards for the three months ended March 31, 2014:
		Restricted			Performance			Total			Weighted Average
		Stock Units			Stock Units			Stock Units			Grant Date Fair
											Value per Unit
	Non-vested at December 31, 2013		148,836			319,984			468,820		$	40.3
	Granted		79,219			108,506			187,725		$	37.93
	Credited from dividends		3,470			8,425			11,895		$	38.44
	Vested		(42,381	)		(132,317	)		(174,698	)	$	40.08
	Forfeited		(2,485	)		(6,205	)		(8,690	)	$	40.26
	Non-vested at March 31, 2014		186,659			298,393			485,052		$	39.41
	Stock options to most executive officers vest and become exercisable upon the completion of a three-year service period commencing on the grant date. The stock options have a term of 10 years. In the event of termination of employment, other than retirement, death or disability, any non-vested options are forfeited for most participants. 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 for most participants. There are special vesting provisions for the stock options related to a change in control.
	In accordance with accounting standards, compensation expense for non-vested stock options is recorded over the vesting period based on the fair value at the date of grant. The fair value of stock options on the date of grant is calculated using the Black-Scholes-Merton model and the assumptions listed below:
		February 2014 Grant			February 2013 Grant			February 2012 Grant
	Grant date price per share of option award	$	37.93		$	42.76		$	38.21
	Expected dividend yield per share		2.75	%		2.75	%		2.75	%
	Expected life in years		6.5			6.5			6.5
	Expected volatility		52.14	%		53.77	%		55.06	%
	Risk-free interest rate		1.98	%		1.29	%		1.34	%
	Grant date fair value per share of option awards	$	15.26		$	17.28		$	15.82
	The dividend yield is based on the Company’s current and prospective dividend rate which calculates a continuous dividend yield based upon the market price of the underlying common stock. The expected life in years is based on the simplified method permitted under Securities and Exchange Commission Staff Accounting Bulletin No. 14d.2 which calculates the average of the weighted vesting term and the contractual term of the option. This method was selected due to the lack of historical exercise data with respect to 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, 2014:
		Options			Weighted Average			Weighted Average			Aggregate Intrinsic
					Exercise Price			Remaining			Value (in millions)
					per Option			Contractual Term
								(in years)
	Outstanding at December 31, 2013		421,080		$	35.96
	Granted		106,658		$	37.93
	Forfeited		(8,747	)	$	40.42
	Outstanding at March 31, 2014		518,991		$	36.29			7.25		$	2.7
	Exercisable at March 31, 2014		235,231		$	32.35			6.01		$	2.1
	Total stock-based compensation expense recognized for the three months ended March 31, 2014 and 2013 is as follows:
		Three Months Ended March 31,
		2014			2013
	(Dollars in millions)
	Stock-based compensation expense recognized:
	Selling, general and administrative expenses	$	1.2		$	1.4
	Less related income tax benefit		0.5			0.6
		$	0.7		$	0.8
	As of March 31, 2014, total future compensation expense related to non-vested stock-based compensation arrangements totaled $11.2 million and the weighted-average period over which this cost is expected to be recognized is approximately 26 months.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2014
Segment Reporting [Abstract]	'
Segment Information	'
	9. Segment Information
	The Company has two reportable segments: Carbon Materials and Chemicals and Railroad and Utility Products and Services. The Company’s reportable segments contain business units that offer different products. The reportable segments are each managed separately because they manufacture and distribute distinct products with different production processes. The business units have been aggregated into two reportable segments since management believes the long-term financial performance of these business units is affected by similar economic conditions.
	The Company’s Carbon Materials and Chemicals segment is primarily a manufacturer of carbon pitch, naphthalene, phthalic anhydride, creosote and carbon black feedstock. 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. Creosote is used in the treatment of wood and carbon black feedstock is used in the production of carbon black.
	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 include procuring and treating items such as crossties, switch ties and various types of lumber used for railroad bridges and crossings and the manufacture of rail joint bars. Utility products include transmission and distribution poles and pilings.
	The Company 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 or income taxes. Operating profit also excludes the operating costs of Koppers Holdings Inc., the parent company of Koppers Inc. The accounting policies of the reportable segments are the same as those described in the summary of significant accounting policies. Intersegment transactions are eliminated in consolidation.
	The following table sets forth certain sales and operating data, net of all intersegment transactions, for the Company’s segments for the periods indicated:
			Three Months Ended March 31,
			2014			2013
	(Dollars in millions)
	Revenues from external customers:
	Carbon Materials and Chemicals		$	202.6		$	230.5
	Railroad and Utility Products and Services			128.8			139.9
	Total		$	331.4		$	370.4
	Intersegment revenues:
	Carbon Materials and Chemicals		$	21.2		$	21.9
	Depreciation and amortization expense(a):
	Carbon Materials and Chemicals		$	6.1		$	4.5
	Railroad and Utility Products and Services			2.8			2.8
	Total		$	8.9		$	7.3
	Operating profit:
	Carbon Materials and Chemicals(b)		$	(8.8	)	$	13.1
	Railroad and Utility Products and Services			11.1			12.3
	Corporate(c)			(1.8	)		(0.5	)
	Total		$	0.5		$	24.9
	(a)	Excludes impairment charges of $4.7 million in 2014 for Carbon Materials and Chemicals.
	(b)	Includes plant closure costs of $10.8 million in 2014 for the Uithoorn, the Netherlands facility and impairment charges of $4.7 million in 2014 for the Tangshan, China facility.
	(c)	Operating loss for Corporate includes general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc.
	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,			December 31,
			2014			2013
	(Dollars in millions)
	Segment assets:
	Carbon Materials and Chemicals		$	523.7		$	535.5
	Railroad and Utility Products and Services			228.6			179.3
	All other			48.9			70.1
	Total		$	801.2		$	784.9
	Goodwill:
	Carbon Materials and Chemicals		$	68.7		$	68
	Railroad and Utility Products and Services			6.3			4.7
	Total		$	75		$	72.7

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	10. Income Taxes
	Effective Tax Rate
	The income tax provision for interim periods is based on an estimated annual effective tax rate, which requires management to make its best estimate of annual pretax income by domestic and foreign jurisdictions and other items that impact taxable income. Items that are not related to annual pretax ordinary income are recognized entirely in the interim period as a discrete item.
	Income taxes as a percentage of pretax ordinary income was 72.9 percent and 38.5 percent for each of the three months ended March 31, 2014 and 2013, respectively, before discrete items. Discrete items included in income taxes for the three months ended March 31, 2014 were a net tax benefit of $5.5 million which was primarily related to management’s decision that a deferred tax liability for certain undistributed earnings of its European subsidiaries was no longer necessary as these earnings are permanently reinvested. There were no material discrete items included in income taxes for the three months ended March 31, 2013.
	The effective tax rate for the three months ended on March 31, 2014 differs from the U.S. federal statutory rate of 35.0 percent due to the taxes on foreign earnings (+34.8 percent), state taxes (+3.6 percent), nondeductible expenses (+1.8 percent), and uncertain tax expenses (+1.1 percent) partially offset by the domestic manufacturing deduction (-3.4 percent). With respect to the three months ended on March 31, 2013, the effective tax rate differs from the U.S. federal statutory rate of 35.0 percent due to the taxes on foreign earnings (+2.4 percent), state taxes (+1.7 percent), uncertain tax expenses (+0.7 percent), and nondeductible expenses (+0.6 percent) partially offset by the domestic manufacturing deduction (-1.9 percent).
	During the year, management regularly updates estimates based on changes in various factors such as product prices, shipments, product mix, operating and administrative costs, earnings mix by taxable jurisdiction, repatriation of foreign earnings, uncertain tax positions and the ability to claim tax credits. To the extent that actual results vary from the estimates at the end of the first quarter, the actual tax provision recognized for 2014 could be materially different from the forecasted annual tax provision as of the end of the first quarter.
	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 before 2008.
	As of March 31, 2014 and December 31, 2013, the total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate, was approximately $4.6 million and $4.5 million, respectively. Unrecognized tax benefits totaled $6.1 million and $6.1 million as of March 31, 2014 and December 31, 2013, respectively. The Company recognizes interest expense and any related penalties from uncertain tax positions in income tax expense. As of March 31, 2014 and December 31, 2013 the Company had accrued approximately $1.3 million and $1.2 million for interest and penalties, respectively.

Inventories

Inventories	3 Months Ended
	Mar. 31, 2014
Inventory Disclosure [Abstract]	'
Inventories	'
	11. Inventories
	Net inventories as of March 31, 2014 and December 31, 2013 are summarized in the table below:
		March 31,		December 31,
		2014		2013
	(Dollars in millions)
	Raw materials	$	119.1	$	105.4
	Work in process		18.2		19.2
	Finished goods		107.5		94.8
			244.8		219.4
	Less revaluation to LIFO		51.6		50.6
	Net	$	193.2	$	168.8

Property_Plant_and_Equipment

Property, Plant and Equipment	3 Months Ended
	Mar. 31, 2014
Property Plant And Equipment [Abstract]	'
Property, Plant and Equipment	'
	12. Property, Plant and Equipment
	Property, plant and equipment as of March 31, 2014 and December 31, 2013 are summarized in the table below:
		March 31,		December 31,
		2014		2013
	(Dollars in millions)
	Land	$	9.6	$	9.1
	Buildings		31.1		30.6
	Machinery and equipment		624		608.1
			664.7		647.8
	Less accumulated depreciation		462.2		450.8
	Net	$	202.5	$	197
	Impairment – Impairment charges for the three months ended March 31, 2014 were $4.7 million ($2.8 million, net of non-controlling interest) and were related to the Carbon Material and Chemicals’ plant in Tangshan, China. This impairment charge was calculated using a probability-weighted discounted cash flow model.
	The impairment of the Company’s 60-percent owned plant in Tangshan, China is due to the forced closure of a neighboring metallurgical coke facility. In October 2013, the Company was informed by the Tangshan Municipal People’s Government (“Tangshan Government”) of its intention to close the two coke batteries owned and operated by the Tangshan Iron and Steel Group Co., Ltd (“TISCO”) in Tangshan, China. The Tangshan Government has ordered the closure of these coke batteries in an effort to improve the air quality in the Tangshan area. The Company was notified in March 2014 by TISCO that all coke batteries would cease production no later than the end of June 2014.
	The Company’s 60-percent owned subsidiary, Koppers (China) Carbon & Chemical Company Limited (“KCCC”) is located near to TISCO’s coke facililty and relies on its operations for a significant portion of raw material supply, utilities and other shared services. Closure of the TISCO coke batteries directly impacts KCCC’s ability to operate its coal tar distillation plant and the Company has determined that it is unable to continue coal tar distillation activities at the site once TISCO ceases production activities at the adjacent facility. The Company is continuing to evaluate its options, which include transitioning to a new location or entering into other strategic partnerships with other unrelated coal tar distillation companies.
	The closure of KCCC’s coal tar distillation facility would have a material adverse effect on the Company’s business, financial condition, cash flow and results of operations. For the most recent year ended December 31, 2013, KCCC contributed operating profit of approximately $3.3 million after deducting profit attributable to non-controlling interests and excluding asset impairment charges. As of March 31, 2014, the remaining net book value of fixed assets subject to impairment was $2.5 million. This amount will be reflected in depreciation expense over the next four months on an accelerated basis reflecting management’s estimate of the remaining useful life of the assets.
	The Company believes it would be able to continue fulfilling current domestic Chinese customers and its export commitments with capacity at Koppers (Jiangsu) Carbon Chemical Company Limited, which is scheduled for production start-up in mid-2014, its other 30-percent owned Chinese company and other commercial relationships in China. However, the Company’s margin on export sales may be negatively affected as a result of these actions.

Pensions_and_Postretirement_Be

Pensions and Postretirement Benefit Plans	3 Months Ended
	Mar. 31, 2014
Compensation And Retirement Disclosure [Abstract]	'
Pensions and Postretirement Benefit Plans	'
	13. Pensions and Postretirement 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.
	All qualified defined benefit pension plans for salaried employees have been closed to new participants and a number of plans, including most plans for hourly employees, have been frozen or are scheduled to be frozen in the next two years. Accordingly, these pension plans no longer accrue additional years of service or recognize future increases in compensation for benefit purposes. In addition, a number of pension plans are subject to a “soft” freeze which precludes new employees from entering the defined benefit pension plans.
	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 and other benefit plans for the three months ended March 31, 2014 and 2013:
		Three Months Ended March 31,
		2014			2013
	(Dollars in millions)
	Service cost	$	0.6		$	0.9
	Interest cost		2.9			2.7
	Expected return on plan assets		(3.5	)		(3.2	)
	Amortization of net loss		1			1.9
	Net periodic benefit cost for defined benefit plans	$	1		$	2.3
	Defined contribution plan expense	$	1.7		$	1.5
	Other postretirement benefit plan expense		0.1			0.1
	Multi-employer pension plan expense		0.1			0.1

Debt

Debt	3 Months Ended
	Mar. 31, 2014
Debt Disclosure [Abstract]	'
Debt	'
	14. Debt
	Debt at March 31, 2014 and December 31, 2013 was as follows:
		Weighted			Maturity		March 31,		December 31,
		Average					2014		2013
		Interest Rate
	(Dollars in millions)
	Revolving Credit Facility		1.91	%		2018	$	15	$	0
	Construction loans		6.24	%		2018	$	28.3	$	6.6
	Senior Notes		7 7/8	%		2019		296.7		296.5
	Total debt							340		303.1
	Less short term debt and current maturities of long-term debt							0		0
	Long-term debt						$	340	$	303.1
	Revolving Credit Facility
	The Koppers Inc. revolving credit facility agreement provides for a revolving credit facility of up to $350.0 million 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 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. Commitment fees totaled $0.3 million for both of the three months ended March 31, 2014 and March 31, 2013 and are charged to interest expense.
	As of March 31, 2014, the Company had $299.8 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, 2014, $35.2 million of commitments were utilized by outstanding letters of credit.
	Construction Loans
	On November 18, 2013, the Company’s 75-percent owned subsidiary, Koppers (Jiangsu) Carbon Chemical Company limited (“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 Company’s Revolving Credit Facility. The committed facilities will be used to finance the costs related to the construction of the coal tar distillation plant in Pizhou, Jiangsu province in China. The facilities are variable rate and have certain financial covenants that monitor minimum net worth and leverage. KJCC will repay the loans in six installments every six months starting in May 2016 with a final repayment on November 18, 2018, the maturity date of the loans.
	Senior Notes
	The Koppers Inc. 7 7/8 percent Senior Notes due 2019 (the “Senior Notes”) were issued on December 1, 2009 at an offering price of 98.311 percent of face value, or $294.9 million and have a principal amount at maturity of $300.0 million. The Senior Notes have an effective interest rate yield of 8 1/8 percent per annum. The Senior Notes are unsecured senior obligations that are fully and unconditionally guaranteed by Koppers Holdings and certain of Koppers Inc.’s wholly-owned domestic subsidiaries. The Senior Notes are structurally subordinated to indebtedness under the revolving credit facility.
	Interest on the Senior Notes is payable semiannually on December 1 and June 1 each year. On or after December 1, 2014, the Company is entitled to redeem all or a portion of the Senior Notes at a redemption price of 103.938 percent of principal value, declining annually in ratable amounts until the redemption price is equivalent to the principal value on December 1, 2017.
	The indenture governing the 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.

Asset_Retirement_Obligations

Asset Retirement Obligations	3 Months Ended
	Mar. 31, 2014
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; and cleaning costs for leased rail cars and barges. The following table reflects changes in the carrying values of asset retirement obligations:
		March 31,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	23.2		$	21.5
	Accretion expense		0.5			1.2
	Revision in estimated cash flows, net		0.8			6.7
	Expenses incurred		(1.4	)		(5.6	)
	Currency translation		0.2			(0.6	)
	Balance at end of period	$	23.3		$	23.2

Deferred_Revenue_from_Extended

Deferred Revenue from Extended Product Warranty Liabilities	3 Months Ended
	Mar. 31, 2014
Revenue Recognition [Abstract]	'
Deferred Revenue from Extended Product Warranty Liabilities	'
	16. Deferred Revenue from Extended Product Warranty Liabilities
	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,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	3.2		$	3.9
	Revenue earned		(0.2	)		(0.7	)
	Balance at end of period	$	3		$	3.2

Commitments_and_Contingent_Lia

Commitments and Contingent Liabilities	3 Months Ended
	Mar. 31, 2014
Commitments And Contingencies Disclosure [Abstract]	'
Commitments and Contingent Liabilities	'
	17. Commitments and Contingent Liabilities
	The Company and its subsidiaries are involved in litigation and various proceedings relating to environmental laws and regulations and 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., along with other defendants, is currently a defendant in lawsuits filed in three 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 approximately 111 plaintiffs in 61 cases pending as of March 31, 2014 as compared to 111 plaintiffs in 61 cases pending as of December 31, 2013. As of December 31, 2013, there are a total of 57 cases pending in state court in Pennsylvania, three in Arkansas, and one case pending in state court in Tennessee.
	The plaintiffs in all 61 pending cases seek to recover compensatory damages, while plaintiffs in 56 cases also seek to recover punitive damages. The plaintiffs in the 57 cases filed in Pennsylvania state court seek unspecified damages in excess of the court’s minimum jurisdictional limit. The plaintiffs in the Arkansas state court cases each seek compensatory damages in excess of $50,000 in addition to punitive damages. The plaintiffs in the Tennessee state court case each seek damages of $15.0 million. The other defendants in these lawsuits vary from case to case and include companies such as Beazer East, Inc., United States Steel Corporation, Honeywell International Inc., Vertellus Specialties Inc., Dow Chemical Company, UCAR Carbon Company, Inc., Exxon Mobil Corporation, SGL Carbon Corporation and Alcoa, Inc. Discovery is proceeding in these cases. No trial dates have been set in any of these cases.
	The Company has not provided a reserve for these lawsuits because, at this time, the Company cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. The timing of resolution of these cases cannot be reasonably determined. Although Koppers Inc. is vigorously defending these cases, an unfavorable resolution of these matters may have a material adverse effect on the Company’s business, financial condition, cash flows and results of operations.
	Gainesville. Koppers Inc. operated a utility pole treatment plant in Gainesville from December 29, 1988 until its closure in 2009. The property upon which the utility pole treatment plant was located was sold by Koppers Inc. to Beazer East, Inc. in 2010.
	In November 2010, a class action complaint was filed in the Circuit Court of the Eighth Judicial Circuit located in Alachua County, Florida by residential real property owners located in a neighborhood west of and immediately adjacent to the former utility pole treatment plant in Gainesville. The complaint named Koppers Holdings Inc., Koppers Inc., Beazer East and several other parties as defendants. In a second amended complaint, plaintiffs define the putative class as consisting of all persons who are present record owners of residential real properties located in an area within a two-mile radius of the former Gainesville wood treating plant. Plaintiffs further allege that chemicals and contaminants from the Gainesville plant have contaminated real properties within the two mile geographical area, have caused property damage (diminution in value) and have placed residents and owners of the putative class properties at an elevated risk of exposure to and injury from the chemicals at issue. The second amended complaint seeks damages for diminution in property values, the establishment of a medical monitoring fund and punitive damages.
	The case was removed to the United States District Court for the Northern District of Florida in December 2010. In May 2013, the Court entered a scheduling order for class certification, which sets out discovery deadlines leading up to motions for class certification and opposition to those motions. Under the terms of the order, depositions relating to class certification will not commence until the court has disposed of all pending motions to dismiss. The district court dismissed Koppers Holdings Inc. in September 2013 on the ground that there was no personal jurisdiction. Plaintiffs’ appeal of the dismissal of Koppers Holdings Inc. was dismissed in December 2013. However, the court has not yet ruled on all pending motions to dismiss filed by other defendants. Therefore, depositions relating to class certification have not yet commenced.
	The Company has not provided a reserve for this matter because, at this time, it cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. The timing of resolution of this case cannot be reasonably determined. Although the Company is vigorously defending this case, an unfavorable resolution of this matter may have a material adverse effect on the Company’s business, financial condition, cash flows and results of operations.
	Other Matters. In July 2012, Koppers Netherlands B.V.’s (“Koppers Netherlands”) coal tar distillation plant suffered a series of electrical disruptions which significantly affected plant operations and prevented the resumption of plant operations for a period of approximately three weeks. As a result of the suspension of operations, the coal tar distillation plant was unable to provide steam and other services to an adjacent unaffiliated plant. This unaffiliated plant and Koppers Netherlands’ plant share certain services and plant infrastructure under a cost sharing agreement. In September 2012, Koppers Netherlands received a business interruption claim from the owner of the unaffiliated plant that included an initial claim for lost profits of approximately $1.7 million. In July 2013 the owner of the unaffiliated plant filed a request for arbitration with the Netherlands Arbitration Institute seeking damages for the business interruption claim plus interest, costs and legal fees. In its statement of claim to the arbitration board, the owner of the unaffiliated facility has claimed damages of at least $3.1 million for these costs. The arbitration hearing has been scheduled for June 2014.
	The Company has not provided a reserve for the claimed lost profits because, at this time, it cannot reasonably determine the probability of such loss, and the amount of such loss, if any, cannot be reasonably estimated. The Company does not currently believe that resolution of this matter will involve a loss contingency that would be material to the financial statements.
	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”). In 1998, the parent company of Beazer East purchased an insurance policy under which the funding and risk of certain environmental and other liabilities relating to the former Koppers Company, Inc. operations of Beazer East (which includes locations purchased from Beazer East by Koppers Inc.) are underwritten by Centre Solutions (a member of the Zurich Group) and Swiss Re. Beazer East is a wholly-owned, indirect subsidiary of Heidelberg Cement AG.
	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 or (“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 include all of the National Priorities List sites 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, 2013, amounts paid by Beazer East as a result of its environmental remediation obligations under the Indemnity have averaged in total approximately $15 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. currently maintains 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 the 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 minimus contributor at the site. Additionally, a separate natural resources damages assessment (“NRDA”) is being conducted by a local trustee group. The NRDA is intended to identify further information necessary to estimate liabilities for remediation based settlements of national resource damages (“NRD”) claims. Koppers Inc. may also incur liabilities under the NRD process and has entered into a separate process to develop an allocation of NRD cost.
	In March 2012, a draft Feasibility Study (“FS”) was submitted to EPA by the Lower Willamette Group, a group of certain PRPs which has been conducting the investigation of the site. The draft FS identifies ten possible remedial alternatives which range in cost from approximately $170 million to $1.8 billion. The FS does not determine who is responsible for remediation costs or select remedies. The FS is under review by the EPA which will issue a final decision on the nature and extent of the final remediation. Responsibility for implementing and funding that work will be decided in the separate allocation process.
	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 minimus party at this site.
	Other than the estimated costs of participating in the PRP group at the Portland Harbor and Newark Bay CERCLA sites totaling $1.0 million at March 31, 2014, the Company has not provided a reserve for these matters because there has not been a determination of the total cost of the investigations, the remediation that will be required, the amount of natural resources damages or how those costs will be allocated among the PRPs. Accordingly, the Company believes that it cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. 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.
	Australian Environmental Matters. Soil and groundwater contamination has been detected at certain of the Company’s Australian facilities. At the Company’s tar distillation facility in Newcastle, New South Wales, Australia, soil contamination from an abandoned underground coal tar pipeline and other groundwater contamination have been detected at a property adjacent to the facility. In 2011, the Company and the owner of the adjacent property reached an agreement in which the Company will contribute $1.6 million and the owner of the adjacent property will contribute $7.5 million toward remediation of the property. The agreement provides that the Company will assume responsibility for the management of the remediation effort and will indemnify the current owner for any remediation costs in excess of its agreed contribution. At the completion of the remediation, the agreement provides that the property will be transferred to the Company. The remediation project commenced in 2011 and the Company has reserved its expected remaining remediation costs of $4.2 million and has recorded a receivable, net of cash collections, from the owner of the adjacent property of $2.8 million as of March 31, 2014.
	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 $5.9 million as of March 31, 2014.
	Environmental Reserves Rollforward. The following table reflects changes in the accrued liability for environmental matters, of which $8.7 million and $8.2 million are classified as current liabilities at March 31, 2014 and December 31, 2013, respectively:
		Period ended
		March 31,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	11.9		$	14.1
	Expense		0.1			1.8
	Reversal of reserves		0			(1.2	)
	Cash expenditures		(0.1	)		(0.9	)
	Currency translation		0.5			(1.9	)
	Balance at end of period	$	12.4		$	11.9

Subsidiary_Guarantor_Informati

Subsidiary Guarantor Information for Koppers Inc. Senior Notes	3 Months Ended
	Mar. 31, 2014
Text Block [Abstract]	'
Subsidiary Guarantor Information for Koppers Inc. Senior Notes	'
	18. Subsidiary Guarantor Information for Koppers Inc. Senior Notes
	On December 1, 2009, Koppers Inc. issued $300.0 million principal value of Senior Notes. Koppers Holdings and each of Koppers Inc.’s 100 percent-owned material domestic subsidiaries other than Koppers Assurance, Inc. fully and unconditionally guarantee the payment of principal and interest on the Senior Notes. The domestic guarantor subsidiaries include Koppers World-Wide Ventures Corporation, Koppers Delaware, Inc., Koppers Concrete Products, Inc., Concrete Partners, Inc., and Koppers Asia LLC. Non-guarantor subsidiaries are owned directly by Koppers Inc. or are owned directly or indirectly by Koppers World-Wide Ventures Corporation.
	The guarantee of a guarantor subsidiary will be automatically and unconditionally released and discharged in the event of:
		¡		any sale of the capital stock or substantially all of the assets of the guarantor subsidiary;
		¡		the designation of the guarantor subsidiary as an unrestricted subsidiary in accordance with the indenture governing the Senior Notes; and
		¡		the legal defeasance, covenant defeasance or satisfaction and discharge of the indenture governing the Senior Notes.
	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. Koppers Inc.’s credit agreement prohibits it from making dividend payments to Koppers Holdings Inc. unless (1) such dividend payments are permitted by the indenture governing Koppers Inc.’s Senior Notes and (2) no event of default or potential default has occurred or is continuing under the credit agreement. The indenture governing Koppers Inc.’s Senior Notes restricts its ability to finance Koppers Holdings Inc.’s payment of dividends if (1) a default has occurred or would result from such financing, (2) a restricted subsidiary of Koppers Inc. which is not a guarantor under the indenture is not able to incur additional indebtedness (as defined in the indenture), and (3) the sum of all restricted payments (as defined in the indenture) have exceeded the permitted amount (referred to as the “basket”) at such point in time.
	The Koppers Inc. revolving credit facility agreement provides for a revolving credit facility of up to $350.0 million at variable interest 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 contains certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends and 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.
	The amount of restricted net assets unavailable for distribution to Koppers Holdings Inc. by Koppers Inc. totals $154 million as of March 31, 2014. Cash dividends paid to Koppers Holdings Inc. by its subsidiaries totaled $7.3 million and $6.7 million for the three months ended March 31, 2014 and 2013, respectively.
	Separate condensed consolidating financial statement information for Koppers Holdings Inc. (the parent), Koppers Inc., domestic guarantor subsidiaries and non-guarantor subsidiaries as of March 31, 2014 and December 31, 2013 and for the three months ended March 31, 2014 and 2013 is as follows. The condensed consolidating statement of comprehensive income for the three months ended March 31, 2013 has been restated to revise the presentation of net income and related investments in subsidiaries under the equity method of accounting. This restatement changed the previously reported amounts for equity income, other income, interest expense, net income attributable to Koppers, comprehensive income attributable to Koppers and other related subtotals in the following columns: Parent, Koppers Inc., Domestic Guarantor Subsidiaries and Consolidating Adjustments. There was no change to amounts previously reported for the Consolidated totals.
	The condensed consolidating statement of cash flows for the three months ended March 31, 2013 has been restated to revise the presentation of intercompany dividends and intercompany lending agreements. This restatement changed the previously reported amounts for cash provided by or used in operating activities, investing activities and financing activities in the following columns: Koppers Inc., Domestic Guarantor Subsidiaries, Non-Guarantor Subsidiaries and Consolidating Adjustments. There was no change to amounts previously reported for the Parent or Consolidated columns except for rounding differences. There was no impact on the net increase or decrease in cash for any column.
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended March 31, 2014
			Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
									Guarantor			Subsidiaries			Adjustments
									Subsidiaries
	(Dollars in millions)
	Net sales		$	0		$	177.6		$	10.7		$	153.9		$	(10.8	)	$	331.4
	Cost of sales including depreciation and amortization			0			160.9			6.9			152.5			(10.8	)		309.5
	Selling, general and administrative			0.5			13.5			0.3			7.1			0			21.4
	Operating profit (loss)			(0.5	)		3.2			3.5			(5.7	)		0			0.5
	Other income (expense)			0			0			0.9			0.3			(1.0	)		0.2
	Equity income of subsidiaries			2.5			2.3			(8.2	)		0			3.4			0
	Interest expense (income)			0			6.8			0			1			(1.0	)		6.8
	Income taxes			(0.2	)		(3.7	)		(6.0	)		3.9			0			(6.0	)
	Income from continuing operations			2.2			2.4			2.2			(10.3	)		3.4			(0.1	)
	Noncontrolling interests			0			0			0			(2.3	)		0			(2.3	)
	Net income attributable to Koppers		$	2.2		$	2.4		$	2.2		$	(8.0	)	$	3.4		$	2.2
	Comprehensive income attributable to Koppers		$	5.3		$	5.6		$	4.9		$	0.2		$	(10.7	)	$	5.3
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended March 31, 2013
			Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
									Guarantor			Subsidiaries			Adjustments
									Subsidiaries
	(Dollars in millions)
	Net sales		$	0		$	204.4		$	22.2		$	161.9		$	(18.1	)	$	370.4
	Cost of sales including depreciation and amortization			0			183			17.4			145.4			(18.0	)		327.8
	Selling, general and administrative			0.5			9.7			0.4			7.1			0			17.7
	Operating profit (loss)			(0.5	)		11.7			4.4			9.4			(0.1	)		24.9
	Other income (expense)			0			0.1			1.1			0.4			(1.1	)		0.5
	Equity income of subsidiaries			11.4			11.1			5.6			0			(28.1	)		0
	Interest expense (income)			0.1			6.8			0			1.1			(1.1	)		6.9
	Income taxes			(0.2	)		4.7			0.1			2.5			0			7.1
	Income from continuing operations			11			11.4			11			6.2			(28.2	)		11.4
	Discontinued operations			0			0			0			0.1			0			0.1
	Noncontrolling interests			0			0			0			0.5			0			0.5
	Net income attributable to Koppers		$	11		$	11.4		$	11		$	5.8		$	(28.2	)	$	11
	Comprehensive income attributable to Koppers		$	9.3		$	9.5		$	8.1		$	(3.6	)	$	(14.0	)	$	9.3
	Condensed Consolidating Balance Sheet
	March 31, 2014
			Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
									Guarantor			Subsidiaries			Adjustments
									Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents		$	0		$	0		$	0		$	54.7		$	0		$	54.7
	Receivables, net			0			84.5			3			80.9			0			168.4
	Affiliated receivables			0			5.3			6.3			4.8			(16.4	)		0
	Inventories, net			0			94.5			0			98.9			(0.2	)		193.2
	Deferred tax assets			0			7.9			3.9			0.6			0			12.4
	Other current assets			0			5.8			0.5			34.6			0			40.9
	Total current assets			0			198			13.7			274.5			(16.6	)		469.6
	Equity investments			174.2			338.5			185.2			4.8			(696.0	)		6.7
Property, plant and equipment, net			0			110.8			0.1			91.6			0			202.5
Goodwill			0			39.8			0			35.2			0			75
Deferred tax assets			0			3.8			2.3			8.6			0			14.7
Affiliated loan receivables			0			36.8			146.1			40.5			(223.4	)		0
Other noncurrent assets			0			14.4			0			18.3			0			32.7
Total assets		$	174.2		$	742.1		$	347.4		$	473.5		$	(936.0	)	$	801.2
LIABILITIES AND EQUITY
Accounts payable		$	0.1		$	45.9		$	2.6		$	43.2		$	0		$	91.8
Affiliated payables			0			9.7			1.7			10.2			(21.6	)		0
Accrued liabilities			4.9			30.6			0.3			52.7			0			88.5
Total current liabilities			5			86.2			4.6			106.1			(21.6	)		180.3
Long-term debt			0			311.7			0			28.3			0			340
Affiliated debt			0			111.9			36.8			74.7			(223.4	)		0
Other long-term liabilities			0			63.3			2.6			28.6			0			94.5
Total liabilities			5			573.1			44			237.7			(245.0	)		614.8
Koppers shareholders’ equity			169.2			169			303.4			218.6			(691.0	)		169.2
Noncontrolling interests			0			0			0			17.2			0			17.2
Total liabilities and equity		$	174.2		$	742.1		$	347.4		$	473.5		$	(936.0	)	$	801.2
Condensed Consolidating Balance Sheet
December 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents		$	0		$	29.9		$	0.1		$	52.2		$	0		$	82.2
Receivables, net			0			75.6			9.3			82			0			166.9
Affiliated receivables			0.2			1.1			3.9			2.3			(7.5	)		0
Inventories, net			0			86.1			0			82.9			(0.2	)		168.8
Deferred tax assets			0			7.9			1.5			0.6			0			10
Other current assets			0			7.3			0.6			37.3			0			45.2
Total current assets			0.2			207.9			15.4			257.3			(7.7	)		473.1
Equity investments			174.7			333.5			182.9			4.6			(689.1	)		6.6
Property, plant and equipment, net			0			112.2			0			84.8			0			197
Goodwill			0			39.8			0			32.9			0			72.7
Deferred tax assets			0			2.4			(1.4	)		8.3			0			9.3
Affiliated loan receivables			0			8.5			123.8			40.9			(173.2	)		0
Other noncurrent assets			0			15			0			11.2			0			26.2
Total assets		$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
LIABILITIES AND EQUITY
Accounts payable		$	0		$	48.3		$	6.7		$	52.6		$	0		$	107.6
Affiliated payables			0			1.9			4			8.6			(14.5	)		0
Accrued liabilities			5.1			27.8			0.5			54.1			0			87.5
Total current liabilities			5.1			78			11.2			115.3			(14.5	)		195.1
Long-term debt			0			296.5			0			6.6			0			303.1
Affiliated debt			0			109.5			8.5			55.2			(173.2	)		0
Other long-term liabilities			0			67.6			2.5			26.8			0			96.9
Total liabilities			5.1			551.6			22.2			203.9			(187.7	)		595.1
Koppers shareholders’ equity			169.8			167.7			298.5			216.1			(682.3	)		169.8
Noncontrolling interests			0			0			0			20			0			20
Total liabilities and equity		$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
Condensed Consolidating Statement of Cash Flows
For the Three Months Ended March 31, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities		$	7		$	(8.0	)	$	5.8		$	(6.7	)	$	(11.8	)	$	(13.7	)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions			0			(3.2	)		(14.9	)		(41.1	)		14.8			(44.4	)
(Loans to) repayments from affiliates			0			(28.5	)		(19.5	)		0.4			47.6			0
Net cash proceeds (payments) from divestitures and asset sales			0			0			0			0			0			0
Net cash provided by (used in) investing activities			0			(31.7	)		(34.4	)		(40.7	)		62.4			(44.4	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt			0			15			0			22.2			0			37.2
Borrowings (repayments) of affiliated debt			0			2.1			28.5			17			(47.6	)		0
Dividends paid			(5.0	)		(7.3	)		0			(4.5	)		11.8			(5.0	)
Stock issued (repurchased)			(2.0	)		0			0			14.8			(14.8	)		(2.0	)
Net cash provided by (used in) financing activities			(7.0	)		9.8			28.5			49.5			(50.6	)		30.2
Effect of exchange rates on cash			0			0			0			0.4			0			0.4
Net increase (decrease) in cash and cash equivalents			0			(29.9	)		(0.1	)		2.5			0			(27.5	)
Cash and cash equivalents at beginning of year			0			29.9			0.1			52.2			0			82.2
Cash and cash equivalents at end of period		$	0		$	0		$	0		$	54.7		$	0		$	54.7
Condensed Consolidating Statement of Cash Flows
For the Three Months Ended March 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities		$	6.4		$	5.4		$	4.1		$	(0.4	)	$	(9.8	)	$	5.7
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions			0			(3.5	)		0			(2.9	)		0			(6.4	)
(Loans to) repayments from affiliates			0			0.1			(3.9	)		0.3			3.5			0
Net cash proceeds (payments) from divestitures and asset sales			0			0.1			0			0.1			0			0.2
Net cash provided by (used in) investing activities			0			(3.3	)		(3.9	)		(2.5	)		3.5			(6.2	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of affiliated debt			0			3.6			(0.1	)		0			(3.5	)		0
Deferred financing costs			0			(1.1	)		0			0			0			(1.1	)
Dividends paid			(5.0	)		(6.7	)		0			(3.1	)		9.8			(5.0	)
Stock issued (repurchased)			(1.4	)		0			0			0			0			(1.4	)
Net cash provided by (used in) financing activities			(6.4	)		(4.2	)		(0.1	)		(3.1	)		6.3			(7.5	)
Effect of exchange rates on cash			0			0			0			(2.0	)		0			(2.0	)
Net increase (decrease) in cash and cash equivalents			0			(2.1	)		0.1			(8.0	)		0			(10.0	)
Cash and cash equivalents at beginning of year			0			4.8			0			61.9			0			66.7
Cash and cash equivalents at end of period		$	0		$	2.7		$	0.1		$	53.9		$	0		$	56.7

Subsidiary_Guarantor_Informati1

Subsidiary Guarantor Information for Shelf Registration	3 Months Ended
	Mar. 31, 2014
Text Block [Abstract]	'
Subsidiary Guarantor Information for Shelf Registration	'
	19. Subsidiary Guarantor Information for 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 and units, from time to time in one or more offerings. In addition, Koppers Inc. may sell debt securities from time to time under the registration statement. Debt securities may be fully and unconditionally guaranteed, on a joint and several basis, by Koppers Holdings, Koppers Inc. and/or other guarantor subsidiaries which will correspond to certain subsidiaries in the United States, Europe and Australia which are 100 percent owned by either Koppers Holdings or Koppers Inc. The non-guarantor subsidiaries consist of certain subsidiaries in the United States, China, India and Mauritius. Non-guarantor subsidiaries are owned directly by Koppers Inc. or are owned directly or indirectly by foreign guarantor subsidiaries. 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.
	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. Koppers Inc.’s credit agreement prohibits it from making dividend payments to Koppers Holdings Inc. unless (1) such dividend payments are permitted by the indenture governing Koppers Inc.’s Senior Notes and (2) no event of default or potential default has occurred or is continuing under the credit agreement. The indenture governing Koppers Inc.’s Senior Notes restricts its ability to finance Koppers Holdings Inc.’s payment of dividends if (1) a default has occurred or would result from such financing, (2) a restricted subsidiary of Koppers Inc. which is not a guarantor under the indenture is not able to incur additional indebtedness (as defined in the indenture), and (3) the sum of all restricted payments (as defined in the indenture) have exceeded the permitted amount (referred to as the “basket”) at such point in time.
	The Koppers Inc. revolving credit facility agreement provides for a revolving credit facility of up to $350.0 million at variable interest 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 contains certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends and 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.
	The amount of restricted net assets unavailable for distribution to Koppers Holdings Inc. by its subsidiaries totals approximately $154 million as of March 31, 2014. Cash dividends paid to Koppers Holdings Inc. by its subsidiaries totaled $7.3 million and $6.7 million for the three months ended March 31, 2014 and 2013, respectively.
	Separate condensed consolidating financial statement information for the parent, Koppers Inc., domestic guarantor subsidiaries, foreign guarantor subsidiaries and non-guarantor subsidiaries as of March 31, 2014 and December 31, 2013 and for the three months ended March 31, 2014 and 2013 is as follows. The condensed consolidating statement of comprehensive income for the three months ended March 31, 2013 has been restated to revise the presentation of net income and related investments in subsidiaries under the equity method of accounting. This restatement changed the previously reported amounts for equity income, other income, interest expense, net income attributable to Koppers, comprehensive income attributable to Koppers and other related subtotals in the following columns: Koppers Inc., Domestic Guarantor Subsidiaries, Foreign Guarantor Subsidiaries and Consolidating Adjustments. There was no change to amounts previously reported for the Consolidated totals.
	The condensed consolidating statement of cash flows for the three months ended March 31, 2013 has been restated to revise the presentation of intercompany dividends and intercompany lending agreements. This restatement changed the previously reported amounts for cash provided by or used in operating activities, investing activities and financing activities in the following columns: Koppers Inc., Domestic Guarantor Subsidiaries, Foreign Guarantor Subsidiaries, Non-Guarantor Subsidiaries and Consolidating Adjustments. There was no change to amounts previously reported for the Parent or Consolidated columns except for rounding differences. There was no impact on the net increase or decrease in cash for any column.
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended March 31, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	177.6		$	10.7		$	113.1		$	40.8		$	(10.8	)	$	331.4
	Cost of sales including depreciation and amortization		0			160.9			6.9			108.1			44.4			(10.8	)		309.5
	Selling, general and administrative		0.5			13.5			0.3			5.8			1.3			0			21.4
	Operating profit (loss)		(0.5	)		3.2			3.5			(0.8	)		(4.9	)		0			0.5
	Other income (expense)		0			0			0.9			0			0.3			(1.0	)		0.2
	Equity income of subsidiaries		2.5			2.3			(8.2	)		(3.4	)		0			6.8			0
	Interest expense (income)		0			6.8			0			0.6			0.4			(1.0	)		6.8
	Income taxes		(0.2	)		(3.7	)		(6.0	)		3.3			0.6			0			(6.0	)
	Income from continuing operations		2.2			2.4			2.2			(8.1	)		(5.6	)		6.8			(0.1	)
	Discontinued operations		0			0			0			0			0			0			0
	Noncontrolling interests		0			0			0			0			(2.3	)		0			(2.3	)
	Net income attributable to Koppers	$	2.2		$	2.4		$	2.2		$	(8.1	)	$	(3.3	)	$	6.8		$	2.2
	Comprehensive income attributable to Koppers	$	5.3		$	5.6		$	4.9		$	(6.1	)	$	(0.9	)	$	(3.5	)	$	5.3
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended March 31, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	204.4		$	22.2		$	121.5		$	40.7		$	(18.4	)	$	370.4
	Cost of sales including depreciation and amortization		0			183			17.4			107.7			38			(18.3	)		327.8
	Selling, general and administrative		0.5			9.7			0.4			6			1.1			0			17.7
	Operating profit (loss)		(0.5	)		11.7			4.4			7.8			1.6			(0.1	)		24.9
	Other income (expense)		0			0.1			1.1			0			0.4			(1.1	)		0.5
	Equity income of subsidiaries		11.4			11.1			5.6			0.5			0			(28.6	)		0
	Interest expense (income)		0.1			6.8			0			0.8			0.3			(1.1	)		6.9
	Income taxes		(0.2	)		4.7			0.1			2			0.5			0			7.1
	Income from continuing operations		11			11.4			11			5.5			1.2			(28.7	)		11.4
	Discontinued operations		0			0			0			0.1			0			0			0.1
	Noncontrolling interests		0			0			0			0			0.5			0			0.5
	Net income attributable to Koppers	$	11		$	11.4		$	11		$	5.6		$	0.7		$	(28.7	)	$	11
	Comprehensive income attributable to Koppers	$	9.3		$	9.6		$	8.2		$	1.8		$	0.1		$	(19.7	)	$	9.3
	Condensed Consolidating Balance Sheet
	March 31, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	0		$	0		$	41.8		$	12.9		$	0		$	54.7
	Receivables, net		0			84.5			3			51.5			29.4			0			168.4
	Affiliated receivables		0			5.3			6.3			3.6			1.3			(16.5	)		0
	Inventories, net		0			94.5			0			75			23.9			(0.2	)		193.2
	Deferred tax assets		0			7.9			3.9			0			0.6			0			12.4
	Other current assets		0			5.8			0.5			16.8			17.8			0			40.9
	Total current assets		0			198			13.7			188.7			85.9			(16.7	)		469.6
	Equity investments		174.2			338.5			185.2			46.2			4.8			(742.2	)		6.7
	Property, plant and equipment, net		0			110.8			0.1			39.3			52.3			0			202.5
	Goodwill		0			39.8			0			32.4			2.8			0			75
	Deferred tax assets		0			3.8			2.3			5.6			3			0			14.7
Affiliated loan receivables		0			36.8			146.1			0.1			40.4			(223.4	)		0
Other noncurrent assets		0			14.4			0			10.2			8.1			0			32.7
Total assets	$	174.2		$	742.1		$	347.4		$	322.5		$	197.3		$	(982.3	)	$	801.2
LIABILITIES AND EQUITY
Accounts payable	$	0.1		$	45.9		$	2.6		$	32.8		$	10.4		$	0		$	91.8
Affiliated payables		0			9.7			1.7			1.2			9			(21.6	)		0
Accrued liabilities		4.9			30.6			0.3			41.8			10.9			0			88.5
Total current liabilities		5			86.2			4.6			75.8			30.3			(21.6	)		180.3
Long-term debt		0			311.7			0			0			28.3			0			340
Affiliated debt		0			111.9			36.8			57.6			17.1			(223.4	)		0
Other long-term liabilities		0			63.3			2.6			20.4			8.2			0			94.5
Total liabilities		5			573.1			44			153.8			83.9			(245.0	)		614.8
Koppers shareholders’ equity		169.2			169			303.4			168.7			96.2			(737.3	)		169.2
Noncontrolling interests		0			0			0			0			17.2			0			17.2
Total liabilities and equity	$	174.2		$	742.1		$	347.4		$	322.5		$	197.3		$	(982.3	)	$	801.2
Condensed Consolidating Balance Sheet
December 31, 2013
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0		$	29.9		$	0.1		$	43.5		$	8.7		$	0		$	82.2
Receivables, net		0			75.6			9.3			55.5			26.5			0			166.9
Affiliated receivables		0.2			1.1			3.9			0.8			1.6			(7.6	)		0
Inventories, net		0			86.1			0			75.2			7.7			(0.2	)		168.8
Deferred tax assets		0			7.9			1.5			0			0.6			0			10
Other current assets		0			7.3			0.6			17.5			19.8			0			45.2
Total current assets		0.2			207.9			15.4			192.5			64.9			(7.8	)		473.1
Equity investments		174.7			333.5			182.9			50.5			4.5			(739.5	)		6.6
Property, plant and equipment, net		0			112.2			0			38.1			46.7			0			197
Goodwill		0			39.8			0			31.5			1.4			0			72.7
Deferred tax assets		0			2.4			(1.4	)		5.5			2.8			0			9.3
Affiliated loan receivables		0			8.5			123.8			0.1			40.8			(173.2	)		0
Other noncurrent assets		0			15			0			9.9			1.3			0			26.2
Total assets	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
LIABILITIES AND EQUITY
Accounts payable	$	0		$	48.3		$	6.7		$	40.6		$	12		$	0		$	107.6
Affiliated payables		0			1.9			4			0.4			8.4			(14.7	)		0
Accrued liabilities		5.1			27.8			0.5			31.4			22.7			0			87.5
Total current liabilities		5.1			78			11.2			72.4			43.1			(14.7	)		195.1
Long-term debt		0			296.5			0			0			6.6			0			303.1
Affiliated debt		0			109.5			8.5			55.2			0			(173.2	)		0
Other long-term liabilities		0			67.6			2.5			19.6			7.2			0			96.9
Total liabilities		5.1			551.6			22.2			147.2			56.9			(187.9	)		595.1
Koppers shareholders’ equity		169.8			167.7			298.5			180.9			85.5			(732.6	)		169.8
Noncontrolling interests		0			0			0			0			20			0			20
Total liabilities and equity	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
Condensed Consolidating Statement of Cash Flows
For the Three Months Ended March 31, 2014
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities	$	7		$	(8.0	)	$	5.8		$	4.8		$	(11.5	)	$	(11.8	)	$	(13.7	)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(3.2	)		(14.9	)		(2.7	)		(38.4	)		14.8			(44.4	)
(Loans to) repayments from affiliates		0			(28.5	)		(19.5	)		0			0.4			47.6			0
Net cash proceeds (payments) from divestitures and asset sales		0			0			0			0			0			0			0
Net cash provided by (used in) investing activities		0			(31.7	)		(34.4	)		(2.7	)		(38.0	)		62.4			(44.4	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0			15			0			0			22.2			0			37.2
Borrowings (repayments) of affiliated debt		0			2.1			28.5			0			17			(47.6	)		0
Dividends paid		(5.0	)		(7.3	)		0			(4.5	)		0			11.8			(5.0	)
Stock issued (repurchased)		(2.0	)		0			0			0			14.8			(14.8	)		(2.0	)
Net cash provided by (used in) financing activities		(7.0	)		9.8			28.5			(4.5	)		54			(50.6	)		30.2
Effect of exchange rates on cash		0			0			0			0.7			(0.3	)		0			0.4
Net increase (decrease) in cash and cash equivalents		0			(29.9	)		(0.1	)		(1.7	)		4.2			0			(27.5	)
Cash and cash equivalents at beginning of year		0			29.9			0.1			43.5			8.7			0			82.2
Cash and cash equivalents at end of period	$	0		$	0		$	0		$	41.8		$	12.9		$	0		$	54.7
Condensed Consolidating Statement of Cash Flows
For the Three Months Ended March 31, 2013
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities	$	6.4		$	5.4		$	4.1		$	3.2		$	(3.6	)	$	(9.8	)	$	5.7
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(3.5	)		0			(1.0	)		(1.9	)		0			(6.4	)
(Loans to) repayments from affiliates		0			0.1			(3.9	)		0			0.3			3.5			0
Net cash proceeds (payments) from divestitures and asset sales		0			0.1			0			0.1			0			0			0.2
Net cash provided by (used in) investing activities		0			(3.3	)		(3.9	)		(0.9	)		(1.6	)		3.5			(6.2	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of affiliated debt		0			3.6			(0.1	)		0			0			(3.5	)		0
Deferred financing costs		0			(1.1	)		0			0			0			0			(1.1	)
Dividends paid		(5.0	)		(6.7	)		0			(3.1	)		0			9.8			(5.0	)
Stock issued (repurchased)		(1.4	)		0			0			0			0			0			(1.4	)
Net cash provided by (used in) financing activities		(6.4	)		(4.2	)		(0.1	)		(3.1	)		0			6.3			(7.5	)
Effect of exchange rates on cash		0			0			0			(2.0	)		0			0			(2.0	)
Net increase (decrease) in cash and cash equivalents		0			(2.1	)		0.1			(2.8	)		(5.2	)		0			(10.0	)
Cash and cash equivalents at beginning of year		0			4.8			0			40.7			21.2			0			66.7
Cash and cash equivalents at end of period	$	0		$	2.7		$	0.1		$	37.9		$	16		$	0		$	56.7

Related_Party_Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2014
Related Party Transactions [Abstract]	'
Related Party Transactions	'
	20. Related Party Transactions
	As of March 31, 2014, the Company has loaned $9.5 million to TKK, a 30-percent owned company in China. The loan is repayable in November 2014.

Plant_Closures_and_Discontinue1

Plant Closures and Discontinued Operations (Tables)	3 Months Ended
	Mar. 31, 2014
Discontinued Operations And Disposal Groups [Abstract]	'
Summary of Restructuring Activities and Related Reserves	'
	Details of the restructuring activities and related reserves are as follows:
		Severance and			Environmental			Site			Other			Total
		employee benefits			remediation			demolition
	(Dollars in millions)
	Reserve at December 31, 2012	$	0.2		$	6.7		$	6.3		$	0.1		$	13.3
	Reversal of accrued charges		(0.1	)		0			(0.3	)		0			(0.4	)
	Cash paid		0			(0.1	)		(2.0	)		(0.1	)		(2.2	)
	Currency translation		0			(1.0	)		(0.7	)		0			(1.7	)
	Reserve at December 31, 2013	$	0.1		$	5.6		$	3.3		$	0		$	9
	Accrual		10			0			0.8			0			10.8
	Cash paid		(0.2	)		0			0			0			(0.2	)
	Currency translation		0.1			0.2			0.2			0			0.5
	Reserve at March 31, 2014	$	10		$	5.8		$	4.3		$	0		$	20.1

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2014
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, 2014 and December 31, 2013 are as follows:
			March 31, 2014				December 31, 2013
			Fair Value		Carrying		Fair Value		Carrying
					Value				Value
	(Dollars in millions)
	Financial assets:
	Cash and cash equivalents, including restricted cash		$	54.7	$	54.7	$	82.2	$	82.2
	Investments and other assets(a)			1.4		1.4		1.4		1.4
	Financial liabilities:
	Long-term debt (including current portion)		$	365.1	$	340	$	331.2	$	303.1
	(a)	Excludes equity method investments.

Comprehensive_Income_and_Equit1

Comprehensive Income and Equity (Tables)	3 Months Ended
	Mar. 31, 2014
Equity [Abstract]	'
Schedule of Comprehensive Income	'
	Total comprehensive income for the three months ended March 31, 2014 and 2013 is summarized in the table below:
		Three Months Ended March 31,
		2014			2013
	(Dollars in millions)
	Net (loss) income	$	(0.1	)	$	11.5
	Other comprehensive income (loss):
	Change in currency translation adjustment		(0.3	)		(3.5	)
	Change in foreign currency transactions of long-term subsidiary investments		2.4			0.7
	Change in unrecognized pension net loss, net of tax expense of $0.2 and $0.6		0.6			1
	Change in unrecognized prior service cost, net of tax expense of $0.0 and $0.0		0			0.1
	Total comprehensive income		2.6			9.8
	Less: comprehensive (loss) income attributable to noncontrolling interests		(2.7	)		0.5
	Comprehensive income attributable to Koppers	$	5.3		$	9.3
Schedule of Change in Equity	'
	The following tables present the change in equity for the three months ended March 31, 2014 and 2013, respectively:
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity
	Balance at December 31, 2013	$	169.8		$	20		$	189.8
	Net income (loss)		2.2			(2.3	)		(0.1	)
	Employee stock plans		1.2			0			1.2
	Other comprehensive income (loss)		3.2			(0.5	)		2.7
	Dividends		(5.2	)		0			(5.2	)
	Repurchases of common stock		(2.0	)		0			(2.0	)
	Balance at March 31, 2014	$	169.2		$	17.2		$	186.4
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity’
	Balance at December 31, 2012	$	150.6		$	17.5		$	168.1
	Net income		11			0.5			11.5
	Issuance of common stock		0.2			0			0.2
	Employee stock plans		1.6			0			1.6
	Other comprehensive income		(1.7	)		0			(1.7	)
	Dividends		(5.4	)		0			(5.4	)
	Repurchases of common stock		(1.6	)		0			(1.6	)
	Balance at March 31, 2013	$	154.7		$	18		$	172.7

Earnings_per_Common_Share_Tabl

Earnings per Common Share (Tables)	3 Months Ended
	Mar. 31, 2014
Earnings Per Share [Abstract]	'
Schedule 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,
		2014		2013
	(Dollars in millions, except share amounts, in thousands, and per share amounts)
	Net income attributable to Koppers	$	2.2	$	11
	Less: Income from discontinued operations		0		0.1
	Income from continuing operations attributable to Koppers	$	2.2	$	10.9
	Weighted average common shares outstanding:
	Basic		20,384		20,667
	Effect of dilutive securities		204		258
	Diluted		20,588		20,925
	Earnings per common share – continuing operations:
	Basic earnings per common share	$	0.11	$	0.53
	Diluted earnings per common share		0.11		0.53
	Other data:
	Antidilutive securities excluded from computation of diluted earnings per common share		235		181

Stockbased_Compensation_Tables

Stock-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Summary of Performance Stock Units	'
	The following table shows a summary of the performance stock units as of March 31, 2014:
	Performance Period	Minimum			Target			Maximum
		Shares			Shares			Shares
	2012 – 2014		0			92,847			139,271
	2013 – 2015		0			90,661			135,992
	2014 – 2016		0			108,506			162,759
Summary of Status and Activity of Non-Vested Stock Awards	'
	The following table shows a summary of the status and activity of non-vested stock awards for the three months ended March 31, 2014:
		Restricted			Performance			Total			Weighted Average
		Stock Units			Stock Units			Stock Units			Grant Date Fair
											Value per Unit
	Non-vested at December 31, 2013		148,836			319,984			468,820		$	40.3
	Granted		79,219			108,506			187,725		$	37.93
	Credited from dividends		3,470			8,425			11,895		$	38.44
	Vested		(42,381	)		(132,317	)		(174,698	)	$	40.08
	Forfeited		(2,485	)		(6,205	)		(8,690	)	$	40.26
	Non-vested at March 31, 2014		186,659			298,393			485,052		$	39.41
Stock Options Fair Value Assumptions	'
	The fair value of stock options on the date of grant is calculated using the Black-Scholes-Merton model and the assumptions listed below:
		February 2014 Grant			February 2013 Grant			February 2012 Grant
	Grant date price per share of option award	$	37.93		$	42.76		$	38.21
	Expected dividend yield per share		2.75	%		2.75	%		2.75	%
	Expected life in years		6.5			6.5			6.5
	Expected volatility		52.14	%		53.77	%		55.06	%
	Risk-free interest rate		1.98	%		1.29	%		1.34	%
	Grant date fair value per share of option awards	$	15.26		$	17.28		$	15.82
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, 2014:
		Options			Weighted Average			Weighted Average			Aggregate Intrinsic
					Exercise Price			Remaining			Value (in millions)
					per Option			Contractual Term
								(in years)
	Outstanding at December 31, 2013		421,080		$	35.96
	Granted		106,658		$	37.93
	Forfeited		(8,747	)	$	40.42
	Outstanding at March 31, 2014		518,991		$	36.29			7.25		$	2.7
	Exercisable at March 31, 2014		235,231		$	32.35			6.01		$	2.1
Schedule of Stock-based Compensation Expense Recognized	'
	Total stock-based compensation expense recognized for the three months ended March 31, 2014 and 2013 is as follows:
		Three Months Ended March 31,
		2014			2013
	(Dollars in millions)
	Stock-based compensation expense recognized:
	Selling, general and administrative expenses	$	1.2		$	1.4
	Less related income tax benefit		0.5			0.6
		$	0.7		$	0.8

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2014
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,
			2014			2013
	(Dollars in millions)
	Revenues from external customers:
	Carbon Materials and Chemicals		$	202.6		$	230.5
	Railroad and Utility Products and Services			128.8			139.9
	Total		$	331.4		$	370.4
	Intersegment revenues:
	Carbon Materials and Chemicals		$	21.2		$	21.9
	Depreciation and amortization expense(a):
	Carbon Materials and Chemicals		$	6.1		$	4.5
	Railroad and Utility Products and Services			2.8			2.8
	Total		$	8.9		$	7.3
	Operating profit:
	Carbon Materials and Chemicals(b)		$	(8.8	)	$	13.1
	Railroad and Utility Products and Services			11.1			12.3
	Corporate(c)			(1.8	)		(0.5	)
	Total		$	0.5		$	24.9
	(a)	Excludes impairment charges of $4.7 million in 2014 for Carbon Materials and Chemicals.
	(b)	Includes plant closure costs of $10.8 million in 2014 for the Uithoorn, the Netherlands facility and impairment charges of $4.7 million in 2014 for the Tangshan, China facility.
	(c)	Operating loss for Corporate includes general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc.
Summary of Tangible and Intangible Assets by Segment	'
	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,			December 31,
			2014			2013
	(Dollars in millions)
	Segment assets:
	Carbon Materials and Chemicals		$	523.7		$	535.5
	Railroad and Utility Products and Services			228.6			179.3
	All other			48.9			70.1
	Total		$	801.2		$	784.9
	Goodwill:
	Carbon Materials and Chemicals		$	68.7		$	68
	Railroad and Utility Products and Services			6.3			4.7
	Total		$	75		$	72.7

Inventories_Tables

Inventories (Tables)	3 Months Ended
	Mar. 31, 2014
Inventory Disclosure [Abstract]	'
Components of Inventories	'
	Net inventories as of March 31, 2014 and December 31, 2013 are summarized in the table below:
		March 31,		December 31,
		2014		2013
	(Dollars in millions)
	Raw materials	$	119.1	$	105.4
	Work in process		18.2		19.2
	Finished goods		107.5		94.8
			244.8		219.4
	Less revaluation to LIFO		51.6		50.6
	Net	$	193.2	$	168.8

Property_Plant_and_Equipment_T

Property, Plant and Equipment (Tables)	3 Months Ended
	Mar. 31, 2014
Property Plant And Equipment [Abstract]	'
Property, Plant and Equipment	'
	Property, plant and equipment as of March 31, 2014 and December 31, 2013 are summarized in the table below:
		March 31,		December 31,
		2014		2013
	(Dollars in millions)
	Land	$	9.6	$	9.1
	Buildings		31.1		30.6
	Machinery and equipment		624		608.1
			664.7		647.8
	Less accumulated depreciation		462.2		450.8
	Net	$	202.5	$	197

Pensions_and_Postretirement_Be1

Pensions and Postretirement Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2014
Compensation And Retirement Disclosure [Abstract]	'
Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans	'
	The following table provides the components of net periodic benefit cost for the pension plans and other benefit plans for the three months ended March 31, 2014 and 2013:
		Three Months Ended March 31,
		2014			2013
	(Dollars in millions)
	Service cost	$	0.6		$	0.9
	Interest cost		2.9			2.7
	Expected return on plan assets		(3.5	)		(3.2	)
	Amortization of net loss		1			1.9
	Net periodic benefit cost for defined benefit plans	$	1		$	2.3
	Defined contribution plan expense	$	1.7		$	1.5
	Other postretirement benefit plan expense		0.1			0.1
	Multi-employer pension plan expense		0.1			0.1

Debt_Tables

Debt (Tables)	3 Months Ended
	Mar. 31, 2014
Debt Disclosure [Abstract]	'
Schedule of Long-Term Debt Instruments	'
	Debt at March 31, 2014 and December 31, 2013 was as follows:
		Weighted			Maturity		March 31,		December 31,
		Average					2014		2013
		Interest Rate
	(Dollars in millions)
	Revolving Credit Facility		1.91	%		2018	$	15	$	0
	Construction loans		6.24	%		2018	$	28.3	$	6.6
	Senior Notes		7 7/8	%		2019		296.7		296.5
	Total debt							340		303.1
	Less short term debt and current maturities of long-term debt							0		0
	Long-term debt						$	340	$	303.1

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	3 Months Ended
	Mar. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]	'
Schedule of Change in Asset Retirement Obligation	'
	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; and cleaning costs for leased rail cars and barges. The following table reflects changes in the carrying values of asset retirement obligations:
		March 31,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	23.2		$	21.5
	Accretion expense		0.5			1.2
	Revision in estimated cash flows, net		0.8			6.7
	Expenses incurred		(1.4	)		(5.6	)
	Currency translation		0.2			(0.6	)
	Balance at end of period	$	23.3		$	23.2

Deferred_Revenue_from_Extended1

Deferred Revenue from Extended Product Warranty Liabilities (Tables)	3 Months Ended
	Mar. 31, 2014
Revenue Recognition [Abstract]	'
Deferred Revenue from Extended Product Warranty Liabilities	'
	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,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	3.2		$	3.9
	Revenue earned		(0.2	)		(0.7	)
	Balance at end of period	$	3		$	3.2

Commitments_and_Contingent_Lia1

Commitments and Contingent Liabilities (Tables)	3 Months Ended
	Mar. 31, 2014
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 $8.7 million and $8.2 million are classified as current liabilities at March 31, 2014 and December 31, 2013, respectively:
		Period ended
		March 31,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	11.9		$	14.1
	Expense		0.1			1.8
	Reversal of reserves		0			(1.2	)
	Cash expenditures		(0.1	)		(0.9	)
	Currency translation		0.5			(1.9	)
	Balance at end of period	$	12.4		$	11.9

Subsidiary_Guarantor_Informati2

Subsidiary Guarantor Information for Koppers Inc. Senior Notes (Tables)	3 Months Ended
	Mar. 31, 2014
Text Block [Abstract]	'
Condensed Consolidating Statement of Comprehensive Income	'
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended March 31, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	177.6		$	10.7		$	153.9		$	(10.8	)	$	331.4
	Cost of sales including depreciation and amortization		0			160.9			6.9			152.5			(10.8	)		309.5
	Selling, general and administrative		0.5			13.5			0.3			7.1			0			21.4
	Operating profit (loss)		(0.5	)		3.2			3.5			(5.7	)		0			0.5
	Other income (expense)		0			0			0.9			0.3			(1.0	)		0.2
	Equity income of subsidiaries		2.5			2.3			(8.2	)		0			3.4			0
	Interest expense (income)		0			6.8			0			1			(1.0	)		6.8
	Income taxes		(0.2	)		(3.7	)		(6.0	)		3.9			0			(6.0	)
	Income from continuing operations		2.2			2.4			2.2			(10.3	)		3.4			(0.1	)
	Noncontrolling interests		0			0			0			(2.3	)		0			(2.3	)
	Net income attributable to Koppers	$	2.2		$	2.4		$	2.2		$	(8.0	)	$	3.4		$	2.2
	Comprehensive income attributable to Koppers	$	5.3		$	5.6		$	4.9		$	0.2		$	(10.7	)	$	5.3
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended March 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	204.4		$	22.2		$	161.9		$	(18.1	)	$	370.4
	Cost of sales including depreciation and amortization		0			183			17.4			145.4			(18.0	)		327.8
	Selling, general and administrative		0.5			9.7			0.4			7.1			0			17.7
	Operating profit (loss)		(0.5	)		11.7			4.4			9.4			(0.1	)		24.9
	Other income (expense)		0			0.1			1.1			0.4			(1.1	)		0.5
	Equity income of subsidiaries		11.4			11.1			5.6			0			(28.1	)		0
	Interest expense (income)		0.1			6.8			0			1.1			(1.1	)		6.9
	Income taxes		(0.2	)		4.7			0.1			2.5			0			7.1
	Income from continuing operations		11			11.4			11			6.2			(28.2	)		11.4
	Discontinued operations		0			0			0			0.1			0			0.1
	Noncontrolling interests		0			0			0			0.5			0			0.5
	Net income attributable to Koppers	$	11		$	11.4		$	11		$	5.8		$	(28.2	)	$	11
	Comprehensive income attributable to Koppers	$	9.3		$	9.5		$	8.1		$	(3.6	)	$	(14.0	)	$	9.3
Condensed Consolidating Balance Sheet	'
	Condensed Consolidating Balance Sheet
	March 31, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	0		$	0		$	54.7		$	0		$	54.7
	Receivables, net		0			84.5			3			80.9			0			168.4
	Affiliated receivables		0			5.3			6.3			4.8			(16.4	)		0
	Inventories, net		0			94.5			0			98.9			(0.2	)		193.2
	Deferred tax assets		0			7.9			3.9			0.6			0			12.4
	Other current assets		0			5.8			0.5			34.6			0			40.9
	Total current assets		0			198			13.7			274.5			(16.6	)		469.6
	Equity investments		174.2			338.5			185.2			4.8			(696.0	)		6.7
	Property, plant and equipment, net		0			110.8			0.1			91.6			0			202.5
	Goodwill		0			39.8			0			35.2			0			75
	Deferred tax assets		0			3.8			2.3			8.6			0			14.7
	Affiliated loan receivables		0			36.8			146.1			40.5			(223.4	)		0
	Other noncurrent assets		0			14.4			0			18.3			0			32.7
	Total assets	$	174.2		$	742.1		$	347.4		$	473.5		$	(936.0	)	$	801.2
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	45.9		$	2.6		$	43.2		$	0		$	91.8
	Affiliated payables		0			9.7			1.7			10.2			(21.6	)		0
	Accrued liabilities		4.9			30.6			0.3			52.7			0			88.5
	Total current liabilities		5			86.2			4.6			106.1			(21.6	)		180.3
	Long-term debt		0			311.7			0			28.3			0			340
	Affiliated debt		0			111.9			36.8			74.7			(223.4	)		0
	Other long-term liabilities		0			63.3			2.6			28.6			0			94.5
	Total liabilities		5			573.1			44			237.7			(245.0	)		614.8
	Koppers shareholders’ equity		169.2			169			303.4			218.6			(691.0	)		169.2
	Noncontrolling interests		0			0			0			17.2			0			17.2
	Total liabilities and equity	$	174.2		$	742.1		$	347.4		$	473.5		$	(936.0	)	$	801.2
	Condensed Consolidating Balance Sheet
	December 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	29.9		$	0.1		$	52.2		$	0		$	82.2
	Receivables, net		0			75.6			9.3			82			0			166.9
	Affiliated receivables		0.2			1.1			3.9			2.3			(7.5	)		0
	Inventories, net		0			86.1			0			82.9			(0.2	)		168.8
	Deferred tax assets		0			7.9			1.5			0.6			0			10
	Other current assets		0			7.3			0.6			37.3			0			45.2
	Total current assets		0.2			207.9			15.4			257.3			(7.7	)		473.1
	Equity investments		174.7			333.5			182.9			4.6			(689.1	)		6.6
	Property, plant and equipment, net		0			112.2			0			84.8			0			197
	Goodwill		0			39.8			0			32.9			0			72.7
	Deferred tax assets		0			2.4			(1.4	)		8.3			0			9.3
	Affiliated loan receivables		0			8.5			123.8			40.9			(173.2	)		0
	Other noncurrent assets		0			15			0			11.2			0			26.2
	Total assets	$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
	LIABILITIES AND EQUITY
	Accounts payable	$	0		$	48.3		$	6.7		$	52.6		$	0		$	107.6
	Affiliated payables		0			1.9			4			8.6			(14.5	)		0
	Accrued liabilities		5.1			27.8			0.5			54.1			0			87.5
	Total current liabilities		5.1			78			11.2			115.3			(14.5	)		195.1
	Long-term debt		0			296.5			0			6.6			0			303.1
	Affiliated debt		0			109.5			8.5			55.2			(173.2	)		0
	Other long-term liabilities		0			67.6			2.5			26.8			0			96.9
	Total liabilities		5.1			551.6			22.2			203.9			(187.7	)		595.1
Koppers shareholders’ equity		169.8			167.7			298.5			216.1			(682.3	)		169.8
Noncontrolling interests		0			0			0			20			0			20
Total liabilities and equity	$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
Condensed Consolidating Statement of Cash Flows	'
	Condensed Consolidating Statement of Cash Flows
	For the Three Months Ended March 31, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	7		$	(8.0	)	$	5.8		$	(6.7	)	$	(11.8	)	$	(13.7	)
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(3.2	)		(14.9	)		(41.1	)		14.8			(44.4	)
	(Loans to) repayments from affiliates		0			(28.5	)		(19.5	)		0.4			47.6			0
	Net cash proceeds (payments) from divestitures and asset sales		0			0			0			0			0			0
	Net cash provided by (used in) investing activities		0			(31.7	)		(34.4	)		(40.7	)		62.4			(44.4	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of long-term debt		0			15			0			22.2			0			37.2
	Borrowings (repayments) of affiliated debt		0			2.1			28.5			17			(47.6	)		0
	Dividends paid		(5.0	)		(7.3	)		0			(4.5	)		11.8			(5.0	)
	Stock issued (repurchased)		(2.0	)		0			0			14.8			(14.8	)		(2.0	)
	Net cash provided by (used in) financing activities		(7.0	)		9.8			28.5			49.5			(50.6	)		30.2
	Effect of exchange rates on cash		0			0			0			0.4			0			0.4
	Net increase (decrease) in cash and cash equivalents		0			(29.9	)		(0.1	)		2.5			0			(27.5	)
	Cash and cash equivalents at beginning of year		0			29.9			0.1			52.2			0			82.2
	Cash and cash equivalents at end of period	$	0		$	0		$	0		$	54.7		$	0		$	54.7
	Condensed Consolidating Statement of Cash Flows
	For the Three Months Ended March 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	6.4		$	5.4		$	4.1		$	(0.4	)	$	(9.8	)	$	5.7
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(3.5	)		0			(2.9	)		0			(6.4	)
	(Loans to) repayments from affiliates		0			0.1			(3.9	)		0.3			3.5			0
	Net cash proceeds (payments) from divestitures and asset sales		0			0.1			0			0.1			0			0.2
	Net cash provided by (used in) investing activities		0			(3.3	)		(3.9	)		(2.5	)		3.5			(6.2	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of affiliated debt		0			3.6			(0.1	)		0			(3.5	)		0
	Deferred financing costs		0			(1.1	)		0			0			0			(1.1	)
	Dividends paid		(5.0	)		(6.7	)		0			(3.1	)		9.8			(5.0	)
	Stock issued (repurchased)		(1.4	)		0			0			0			0			(1.4	)
	Net cash provided by (used in) financing activities		(6.4	)		(4.2	)		(0.1	)		(3.1	)		6.3			(7.5	)
	Effect of exchange rates on cash		0			0			0			(2.0	)		0			(2.0	)
	Net increase (decrease) in cash and cash equivalents		0			(2.1	)		0.1			(8.0	)		0			(10.0	)
	Cash and cash equivalents at beginning of year		0			4.8			0			61.9			0			66.7
	Cash and cash equivalents at end of period	$	0		$	2.7		$	0.1		$	53.9		$	0		$	56.7

Subsidiary_Guarantor_Informati3

Subsidiary Guarantor Information for Shelf Registration (Tables)	3 Months Ended
	Mar. 31, 2014
Text Block [Abstract]	'
Condensed Consolidating Statement of Comprehensive Income	'
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended March 31, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	177.6		$	10.7		$	113.1		$	40.8		$	(10.8	)	$	331.4
	Cost of sales including depreciation and amortization		0			160.9			6.9			108.1			44.4			(10.8	)		309.5
	Selling, general and administrative		0.5			13.5			0.3			5.8			1.3			0			21.4
	Operating profit (loss)		(0.5	)		3.2			3.5			(0.8	)		(4.9	)		0			0.5
	Other income (expense)		0			0			0.9			0			0.3			(1.0	)		0.2
	Equity income of subsidiaries		2.5			2.3			(8.2	)		(3.4	)		0			6.8			0
	Interest expense (income)		0			6.8			0			0.6			0.4			(1.0	)		6.8
	Income taxes		(0.2	)		(3.7	)		(6.0	)		3.3			0.6			0			(6.0	)
	Income from continuing operations		2.2			2.4			2.2			(8.1	)		(5.6	)		6.8			(0.1	)
	Discontinued operations		0			0			0			0			0			0			0
	Noncontrolling interests		0			0			0			0			(2.3	)		0			(2.3	)
	Net income attributable to Koppers	$	2.2		$	2.4		$	2.2		$	(8.1	)	$	(3.3	)	$	6.8		$	2.2
	Comprehensive income attributable to Koppers	$	5.3		$	5.6		$	4.9		$	(6.1	)	$	(0.9	)	$	(3.5	)	$	5.3
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended March 31, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	204.4		$	22.2		$	121.5		$	40.7		$	(18.4	)	$	370.4
	Cost of sales including depreciation and amortization		0			183			17.4			107.7			38			(18.3	)		327.8
	Selling, general and administrative		0.5			9.7			0.4			6			1.1			0			17.7
	Operating profit (loss)		(0.5	)		11.7			4.4			7.8			1.6			(0.1	)		24.9
	Other income (expense)		0			0.1			1.1			0			0.4			(1.1	)		0.5
	Equity income of subsidiaries		11.4			11.1			5.6			0.5			0			(28.6	)		0
	Interest expense (income)		0.1			6.8			0			0.8			0.3			(1.1	)		6.9
	Income taxes		(0.2	)		4.7			0.1			2			0.5			0			7.1
	Income from continuing operations		11			11.4			11			5.5			1.2			(28.7	)		11.4
	Discontinued operations		0			0			0			0.1			0			0			0.1
	Noncontrolling interests		0			0			0			0			0.5			0			0.5
	Net income attributable to Koppers	$	11		$	11.4		$	11		$	5.6		$	0.7		$	(28.7	)	$	11
	Comprehensive income attributable to Koppers	$	9.3		$	9.6		$	8.2		$	1.8		$	0.1		$	(19.7	)	$	9.3
Condensed Consolidating Balance Sheet	'
	Condensed Consolidating Balance Sheet
	March 31, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	0		$	0		$	41.8		$	12.9		$	0		$	54.7
	Receivables, net		0			84.5			3			51.5			29.4			0			168.4
	Affiliated receivables		0			5.3			6.3			3.6			1.3			(16.5	)		0
	Inventories, net		0			94.5			0			75			23.9			(0.2	)		193.2
	Deferred tax assets		0			7.9			3.9			0			0.6			0			12.4
	Other current assets		0			5.8			0.5			16.8			17.8			0			40.9
	Total current assets		0			198			13.7			188.7			85.9			(16.7	)		469.6
	Equity investments		174.2			338.5			185.2			46.2			4.8			(742.2	)		6.7
	Property, plant and equipment, net		0			110.8			0.1			39.3			52.3			0			202.5
	Goodwill		0			39.8			0			32.4			2.8			0			75
	Deferred tax assets		0			3.8			2.3			5.6			3			0			14.7
	Affiliated loan receivables		0			36.8			146.1			0.1			40.4			(223.4	)		0
	Other noncurrent assets		0			14.4			0			10.2			8.1			0			32.7
	Total assets	$	174.2		$	742.1		$	347.4		$	322.5		$	197.3		$	(982.3	)	$	801.2
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	45.9		$	2.6		$	32.8		$	10.4		$	0		$	91.8
	Affiliated payables		0			9.7			1.7			1.2			9			(21.6	)		0
	Accrued liabilities		4.9			30.6			0.3			41.8			10.9			0			88.5
	Total current liabilities		5			86.2			4.6			75.8			30.3			(21.6	)		180.3
	Long-term debt		0			311.7			0			0			28.3			0			340
	Affiliated debt		0			111.9			36.8			57.6			17.1			(223.4	)		0
	Other long-term liabilities		0			63.3			2.6			20.4			8.2			0			94.5
	Total liabilities		5			573.1			44			153.8			83.9			(245.0	)		614.8
	Koppers shareholders’ equity		169.2			169			303.4			168.7			96.2			(737.3	)		169.2
	Noncontrolling interests		0			0			0			0			17.2			0			17.2
	Total liabilities and equity	$	174.2		$	742.1		$	347.4		$	322.5		$	197.3		$	(982.3	)	$	801.2
	Condensed Consolidating Balance Sheet
	December 31, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	29.9		$	0.1		$	43.5		$	8.7		$	0		$	82.2
	Receivables, net		0			75.6			9.3			55.5			26.5			0			166.9
	Affiliated receivables		0.2			1.1			3.9			0.8			1.6			(7.6	)		0
	Inventories, net		0			86.1			0			75.2			7.7			(0.2	)		168.8
	Deferred tax assets		0			7.9			1.5			0			0.6			0			10
	Other current assets		0			7.3			0.6			17.5			19.8			0			45.2
	Total current assets		0.2			207.9			15.4			192.5			64.9			(7.8	)		473.1
	Equity investments		174.7			333.5			182.9			50.5			4.5			(739.5	)		6.6
	Property, plant and equipment, net		0			112.2			0			38.1			46.7			0			197
	Goodwill		0			39.8			0			31.5			1.4			0			72.7
	Deferred tax assets		0			2.4			(1.4	)		5.5			2.8			0			9.3
	Affiliated loan receivables		0			8.5			123.8			0.1			40.8			(173.2	)		0
	Other noncurrent assets		0			15			0			9.9			1.3			0			26.2
	Total assets	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
	LIABILITIES AND EQUITY
	Accounts payable	$	0		$	48.3		$	6.7		$	40.6		$	12		$	0		$	107.6
	Affiliated payables		0			1.9			4			0.4			8.4			(14.7	)		0
	Accrued liabilities		5.1			27.8			0.5			31.4			22.7			0			87.5
	Total current liabilities		5.1			78			11.2			72.4			43.1			(14.7	)		195.1
	Long-term debt		0			296.5			0			0			6.6			0			303.1
	Affiliated debt		0			109.5			8.5			55.2			0			(173.2	)		0
	Other long-term liabilities		0			67.6			2.5			19.6			7.2			0			96.9
	Total liabilities		5.1			551.6			22.2			147.2			56.9			(187.9	)		595.1
Koppers shareholders’ equity		169.8			167.7			298.5			180.9			85.5			(732.6	)		169.8
Noncontrolling interests		0			0			0			0			20			0			20
Total liabilities and equity	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
Condensed Consolidating Statement of Cash Flows	'
	Condensed Consolidating Statement of Cash Flows
	For the Three Months Ended March 31, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	7		$	(8.0	)	$	5.8		$	4.8		$	(11.5	)	$	(11.8	)	$	(13.7	)
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(3.2	)		(14.9	)		(2.7	)		(38.4	)		14.8			(44.4	)
	(Loans to) repayments from affiliates		0			(28.5	)		(19.5	)		0			0.4			47.6			0
	Net cash proceeds (payments) from divestitures and asset sales		0			0			0			0			0			0			0
	Net cash provided by (used in) investing activities		0			(31.7	)		(34.4	)		(2.7	)		(38.0	)		62.4			(44.4	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of long-term debt		0			15			0			0			22.2			0			37.2
	Borrowings (repayments) of affiliated debt		0			2.1			28.5			0			17			(47.6	)		0
	Dividends paid		(5.0	)		(7.3	)		0			(4.5	)		0			11.8			(5.0	)
	Stock issued (repurchased)		(2.0	)		0			0			0			14.8			(14.8	)		(2.0	)
	Net cash provided by (used in) financing activities		(7.0	)		9.8			28.5			(4.5	)		54			(50.6	)		30.2
	Effect of exchange rates on cash		0			0			0			0.7			(0.3	)		0			0.4
	Net increase (decrease) in cash and cash equivalents		0			(29.9	)		(0.1	)		(1.7	)		4.2			0			(27.5	)
	Cash and cash equivalents at beginning of year		0			29.9			0.1			43.5			8.7			0			82.2
	Cash and cash equivalents at end of period	$	0		$	0		$	0		$	41.8		$	12.9		$	0		$	54.7
	Condensed Consolidating Statement of Cash Flows
	For the Three Months Ended March 31, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	6.4		$	5.4		$	4.1		$	3.2		$	(3.6	)	$	(9.8	)	$	5.7
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(3.5	)		0			(1.0	)		(1.9	)		0			(6.4	)
	(Loans to) repayments from affiliates		0			0.1			(3.9	)		0			0.3			3.5			0
	Net cash proceeds (payments) from divestitures and asset sales		0			0.1			0			0.1			0			0			0.2
	Net cash provided by (used in) investing activities		0			(3.3	)		(3.9	)		(0.9	)		(1.6	)		3.5			(6.2	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of affiliated debt		0			3.6			(0.1	)		0			0			(3.5	)		0
	Deferred financing costs		0			(1.1	)		0			0			0			0			(1.1	)
	Dividends paid		(5.0	)		(6.7	)		0			(3.1	)		0			9.8			(5.0	)
	Stock issued (repurchased)		(1.4	)		0			0			0			0			0			(1.4	)
	Net cash provided by (used in) financing activities		(6.4	)		(4.2	)		(0.1	)		(3.1	)		0			6.3			(7.5	)
	Effect of exchange rates on cash		0			0			0			(2.0	)		0			0			(2.0	)
	Net increase (decrease) in cash and cash equivalents		0			(2.1	)		0.1			(2.8	)		(5.2	)		0			(10.0	)
	Cash and cash equivalents at beginning of year		0			4.8			0			40.7			21.2			0			66.7
	Cash and cash equivalents at end of period	$	0		$	2.7		$	0.1		$	37.9		$	16		$	0		$	56.7

Dividends_Additional_Informati

Dividends - Additional Information (Detail) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	2-May-14
			Subsequent Event [Member]
Equity [Line Items]	'	'	'
Dividends declared per common share	$0.25	$0.25	$0.25
Common share, dividend payable date	7-Jul-14	'	'
Common share, dividend declared date	2-May-14	'	'
Common share, dividend record date	19-May-14	'	'

Plant_Closures_and_Discontinue2

Plant Closures and Discontinued Operations - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Restructuring Cost and Reserve [Line Items]	'	'	'
Costs related to closure	$10.80	'	'
Impairment charges	4.7	6.9	0
Carbon Materials and Chemicals [Member]	'	'	'
Restructuring Cost and Reserve [Line Items]	'	'	'
Impairment charges	4.7	'	'
Carbon Materials and Chemicals [Member] | Discontinued Operations [Member]	'	'	'
Restructuring Cost and Reserve [Line Items]	'	'	'
Estimated total future closure costs	0.3	'	'
Operating profit from discontinued operation	$0	'	$0.20
Future completion period, closure	'2015	'	'

Plant_Closure_and_Discontinued

Plant Closure and Discontinued Operations - Summary of Restructuring Activities and Related Reserves (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	'	$13.30
Reversal of accrued charges	'	-0.4
Cash paid	-0.2	-2.2
Currency translation	0.5	-1.7
Reserve, Ending Balance	20.1	9
Accrual	'	10.8
Severance and Employee Benefits [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	'	0.2
Reversal of accrued charges	'	-0.1
Cash paid	-0.2	0
Currency translation	0.1	0
Reserve, Ending Balance	10	0.1
Accrual	'	10
Environmental Remediation [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	'	6.7
Reversal of accrued charges	'	0
Cash paid	0	-0.1
Currency translation	0.2	-1
Reserve, Ending Balance	5.8	5.6
Accrual	'	0
Site Demolition [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	'	6.3
Reversal of accrued charges	'	-0.3
Cash paid	0	-2
Currency translation	0.2	-0.7
Reserve, Ending Balance	4.3	3.3
Accrual	'	0.8
Other [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	'	0.1
Reversal of accrued charges	'	0
Cash paid	0	-0.1
Currency translation	0	0
Reserve, Ending Balance	0	0
Accrual	'	$0

Business_Acquisitions_Addition

Business Acquisitions - Additional Information (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2013	Jan. 20, 2014	Jan. 20, 2014	Jan. 20, 2014	Apr. 13, 2014
In Millions, unless otherwise specified			Railroad and Utility Products and Services [Member]	Railroad and Utility Products and Services [Member]	Osmose Holdings Inc [Member]	Tolko Industries Ltd [Member]	Tolko Industries Ltd [Member]	Tolko Industries Ltd [Member]	Subsequent Event [Member]
							Customer Relationships [Member]	Railroad and Utility Products and Services [Member]	Osmose Holdings Inc [Member]
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'	'
Business acquisition purchase price	'	'	'	'	'	$29.60	'	'	$460
Acquired assets consisted of inventory	'	'	'	'	'	16	'	'	'
Acquired assets consisted of plant and equipment	'	'	'	'	'	3.6	'	'	'
Intangible assets consisting primarily of customer relationships	'	'	'	'	'	'	7.4	'	'
Intangible assets consisting deductible goodwill	75	72.7	6.3	4.7	'	'	'	1.6	'
Customer contracts amortization period	'	'	'	'	'	'	'12 years	'	'
Revenues for the acquired businesses	'	'	'	'	$390	'	'	'	'
Cash saving period	'	'	'	'	'	'	'	'	'15 years

Fair_Value_of_Financial_Instru

Fair Value of Financial Instruments - Schedule of Company's Financial Instruments (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Fair Value [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Cash and cash equivalents, including restricted cash	$54.70	$82.20
Investments and other assets	1.4	1.4
Financial liabilities:	'	'
Long-term debt (including current portion)	365.1	331.2
Carrying Value [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Cash and cash equivalents, including restricted cash	54.7	82.2
Investments and other assets	1.4	1.4
Financial liabilities:	'	'
Long-term debt (including current portion)	$340	$303.10

Comprehensive_Income_and_Equit2

Comprehensive Income and Equity - Schedule of Comprehensive Income (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Equity [Abstract]	'	'
Net (loss) income	($0.10)	$11.50
Other comprehensive income (loss):	'	'
Change in currency translation adjustment	-0.3	-3.5
Change in foreign currency transactions of long-term subsidiary investments	2.4	0.7
Change in unrecognized pension net loss, net of tax expense of $0.2 and $0.6	0.6	1
Change in unrecognized prior service cost, net of tax expense of $0.0 and $0.0	0	0.1
Total comprehensive income	2.6	9.8
Less: comprehensive (loss) income attributable to noncontrolling interests	-2.7	0.5
Comprehensive income attributable to Koppers	$5.30	$9.30

Comprehensive_Income_and_Equit3

Comprehensive Income and Equity - Schedule of Comprehensive Income (Parenthetical) (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Equity [Abstract]	'	'
Tax expense, unrecognized pension net loss	$0.20	$0.60
Tax expense, unrecognized prior service cost	$0	$0

Comprehensive_Income_and_Equit4

Comprehensive Income and Equity - Schedule of Change in Equity (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Comprehensive Income And Equity [Line Items]	'	'
Balance	$189.80	$168.10
Net income	-0.1	11.5
Issuance of common stock	'	0.2
Employee stock plans	1.2	1.6
Other comprehensive income (loss)	2.7	-1.7
Dividends	-5.2	-5.4
Repurchases of common stock	-2	-1.6
Balance	186.4	172.7
Total Koppers Shareholders' Equity [Member]	'	'
Comprehensive Income And Equity [Line Items]	'	'
Balance	169.8	150.6
Net income	2.2	11
Issuance of common stock	'	0.2
Employee stock plans	1.2	1.6
Other comprehensive income (loss)	3.2	-1.7
Dividends	-5.2	-5.4
Repurchases of common stock	-2	-1.6
Balance	169.2	154.7
Noncontrolling Interests [Member]	'	'
Comprehensive Income And Equity [Line Items]	'	'
Balance	20	17.5
Net income	-2.3	0.5
Issuance of common stock	'	0
Employee stock plans	0	0
Other comprehensive income (loss)	-0.5	0
Dividends	0	0
Repurchases of common stock	0	0
Balance	$17.20	$18

Earnings_Per_Common_Share_Sche

Earnings Per Common Share - Schedule of Basic and Diluted Earnings Per Common Share (Detail) (USD $)	3 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]	'	'
Net income attributable to Koppers	$2.20	$11
Less: Income from discontinued operations	0	0.1
Income from continuing operations attributable to Koppers	$2.20	$10.90
Weighted average common shares outstanding:	'	'
Basic	20,384	20,667
Effect of dilutive securities	204	258
Diluted	20,588	20,925
Earnings per common share - continuing operations:	'	'
Basic earnings per common share	$0.11	$0.53
Diluted earnings per common share	$0.11	$0.53
Other data:	'	'
Antidilutive securities excluded from computation of diluted earnings per common share	235	181

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2011
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, vesting period in years	'3 years	'
Future compensation expense related to non-vested stock-based compensation arrangements	11.2	'
Future compensation expense, weighted-average expected period of recognition in months	'26 months	'
Performance Stock Units [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Performance stock unit granted in years	'3 years	'2 years
Number of vest performance stock unit, if performance criteria are not achieved	0	'
Minimum [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Percentage of target award the participants earn	0.00%	'
Maximum [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Percentage of target award the participants earn	150.00%	'
Restricted Stock Units [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, vesting period in years	'1 year	'
Employee Stock Option [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, term in years	'10 years	'
Restricted Stock Units (RSUs) [Member] | Performance Stock Units [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, vesting period in years	'3 years	'

StockBased_Compensation_Summar

Stock-Based Compensation - Summary of Performance Stock Units (Detail)	Mar. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	485,052	468,820
Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	298,393	319,984
Minimum Shares [Member] | 2012 - 2014 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	0	'
Minimum Shares [Member] | 2013 - 2015 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	0	'
Minimum Shares [Member] | Two Thousand Fourteen Through Two Thousand Sixteen [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	0	'
Target Shares [Member] | 2012 - 2014 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	92,847	'
Target Shares [Member] | 2013 - 2015 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	90,661	'
Target Shares [Member] | Two Thousand Fourteen Through Two Thousand Sixteen [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	108,506	'
Maximum Shares [Member] | 2012 - 2014 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	139,271	'
Maximum Shares [Member] | 2013 - 2015 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	135,992	'
Maximum Shares [Member] | Two Thousand Fourteen Through Two Thousand Sixteen [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	162,759	'

StockBased_Compensation_Summar1

Stock-Based Compensation - Summary of Status and Activity of Non-Vested Stock Awards (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	468,820
Granted	187,725
Credited from dividends	11,895
Vested	-174,698
Forfeited	-8,690
Non-vested, Ending Balance	485,052
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit	$40.30
Granted, Weighted Average Grant Date Fair Value per Unit	$37.93
Credited from dividends, Weighted Average Grant Date Fair Value per Unit	$38.44
Vested, Weighted Average Grant Date Fair Value per Unit	$40.08
Forfeited, Weighted Average Grant Date Fair Value per Unit	$40.26
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit	$39.41
Restricted Stock Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	148,836
Granted	79,219
Credited from dividends	3,470
Vested	-42,381
Forfeited	-2,485
Non-vested, Ending Balance	186,659
Performance Stock Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	319,984
Granted	108,506
Credited from dividends	8,425
Vested	-132,317
Forfeited	-6,205
Non-vested, Ending Balance	298,393

StockBased_Compensation_Stock_

Stock-Based Compensation - Stock Options Fair Value Assumptions (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014
February 2013 Grant [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Grant date price per share of option award	$37.93
Expected dividend yield per share	2.75%
Expected life in years	'6 years 6 months
Expected volatility	52.14%
Risk-free interest rate	1.98%
Grant date fair value per share of option awards	$15.26
February 2012 Grant [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Grant date price per share of option award	$42.76
Expected dividend yield per share	2.75%
Expected life in years	'6 years 6 months
Expected volatility	53.77%
Risk-free interest rate	1.29%
Grant date fair value per share of option awards	$17.28
February 2011 Grant [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Grant date price per share of option award	$38.21
Expected dividend yield per share	2.75%
Expected life in years	'6 years 6 months
Expected volatility	55.06%
Risk-free interest rate	1.34%
Grant date fair value per share of option awards	$15.82

StockBased_Compensation_Summar2

Stock-Based Compensation - Summary of Status and Activity of Stock Options (Detail) (USD $)	3 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Options Outstanding, Beginning Balance	421,080
Options, Granted	106,658
Options, Exercised	-8,747
Options Outstanding, Ending Balance	518,991
Options Exercisable, Ending Balance	235,231
Outstanding, Weighted Average Exercise Price per Option, Beginning Balance	$35.96
Granted, Weighted Average Exercise Price per Option	$37.93
Exercised, Weighted Average Exercise Price per Option	$40.42
Outstanding, Weighted Average Exercise Price per Option, Ending Balance	$36.29
Exercisable, Weighted Average Exercise Price per Option, Ending Balance	$32.35
Outstanding at March 31, 2014, Weighted Average Remaining Contractual Term	'7 years 3 months
Exercisable at March 31, 2014, Weighted Average Remaining Contractual Term	'6 years 4 days
Outstanding at March 31, 2014, Aggregate Intrinsic Value	$2.70
Exercisable at March 31, 2014, Aggregate Intrinsic Value	$2.10

StockBased_Compensation_Schedu

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Stock-based compensation expense recognized:	'	'
Selling, general and administrative expenses	$1.20	$1.40
Less related income tax benefit	0.5	0.6
Decrease in net income attributable to Koppers	$0.70	$0.80

Segment_Information_Additional

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2014
	Segment
Segment Reporting [Abstract]	'
Number of reportable segments	2

Segment_Information_Summary_of

Segment Information - Summary of Results of Segment Operations (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Revenues from external customers:	'	'
Revenues from external customers	$331.40	$370.40
Intersegment revenues:	'	'
Intersegment revenues	331.4	370.4
Depreciation & amortization(a):	'	'
Depreciation and amortization expense	8.9	7.3
Operating profit:	'	'
Operating profit (loss)	0.5	24.9
Operating Segments [Member] | Carbon Materials and Chemicals [Member]	'	'
Revenues from external customers:	'	'
Revenues from external customers	202.6	230.5
Intersegment revenues:	'	'
Intersegment revenues	202.6	230.5
Depreciation & amortization(a):	'	'
Depreciation and amortization expense	6.1	4.5
Operating profit:	'	'
Operating profit (loss)	-8.8	13.1
Operating Segments [Member] | Railroad and Utility Products and Services [Member]	'	'
Revenues from external customers:	'	'
Revenues from external customers	128.8	139.9
Intersegment revenues:	'	'
Intersegment revenues	128.8	139.9
Depreciation & amortization(a):	'	'
Depreciation and amortization expense	2.8	2.8
Operating profit:	'	'
Operating profit (loss)	11.1	12.3
Intersegment [Member] | Carbon Materials and Chemicals [Member]	'	'
Revenues from external customers:	'	'
Revenues from external customers	21.2	21.9
Intersegment revenues:	'	'
Intersegment revenues	21.2	21.9
Corporate, Non-Segment [Member]	'	'
Operating profit:	'	'
Operating profit (loss)	($1.80)	($0.50)

Segment_Information_Summary_of1

Segment Information - Summary of Results of Segment Operations (Parenthetical) (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Revenue from External Customer [Line Items]	'	'	'
Impairment charges	$4.70	$6.90	$0
Carbon Materials and Chemicals [Member]	'	'	'
Revenue from External Customer [Line Items]	'	'	'
Impairment charges	4.7	'	'
Netherlands Facility [Member]	'	'	'
Revenue from External Customer [Line Items]	'	'	'
Plant Closure cost	10.8	'	'
China Facility [Member]	'	'	'
Revenue from External Customer [Line Items]	'	'	'
Impairment charges	$4.70	'	'

Segment_Information_Summary_of2

Segment Information - Summary of Tangible and Intangible Assets by Segment (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Segment assets:	'	'
Segment assets	$801.20	$784.90
Goodwill:	'	'
Goodwill	75	72.7
Carbon Materials and Chemicals [Member]	'	'
Segment assets:	'	'
Segment assets	523.7	535.5
Goodwill:	'	'
Goodwill	68.7	68
Railroad and Utility Products and Services [Member]	'	'
Segment assets:	'	'
Segment assets	228.6	179.3
Goodwill:	'	'
Goodwill	6.3	4.7
All Other [Member]	'	'
Segment assets:	'	'
Segment assets	$48.90	$70.10

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'	'	'
Percentage of pretax income	72.90%	38.50%	'
Potential income tax examinations	'	$0	'
Net tax benefit included in income taxes, discrete items	5.5	'	'
U.S. federal statutory rate	35.00%	35.00%	'
Taxes on foreign earnings	34.80%	2.40%	'
State taxes	3.60%	1.70%	'
Nondeductible expenses	1.80%	0.60%	'
Domestic manufacturing deduction	3.40%	1.90%	'
Unrecognized tax benefits	1.10%	0.70%	'
Unrecognized tax benefits with impact on the effective tax rate	4.6	'	4.5
Unrecognized tax benefits	6.1	'	6.1
Accrued interest expense and penalties	$1.30	'	$1.20

Inventories_Components_of_Inve

Inventories - Components of Inventories (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Inventory Disclosure [Abstract]	'	'
Raw materials	$119.10	$105.40
Work in process	18.2	19.2
Finished goods	107.5	94.8
Inventories, gross	244.8	219.4
Less revaluation to LIFO	51.6	50.6
Net	$193.20	$168.80

Property_Plant_and_Equipment_P

Property, Plant and Equipment - Property, Plant and Equipment (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	$664.70	$647.80
Less accumulated depreciation	462.2	450.8
Net	202.5	197
Land [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	9.6	9.1
Buildings [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	31.1	30.6
Machinery and Equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	$624	$608.10

Property_Plant_and_Equipment_A

Property, Plant and Equipment - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended				1 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Oct. 31, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Mar. 31, 2014	Oct. 31, 2013	Dec. 31, 2013	Mar. 31, 2014
	Battery				China [Member]	Koppers Carbon and Chemical Company Limited [Member]	Koppers Carbon and Chemical Company Limited [Member]	Koppers Carbon and Chemical Company Limited [Member]
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'	'	'
Impairment charges	'	$4.70	$6.90	$0	'	'	'	'
Assets impairment charges net of non controlling interest	'	2.8	'	'	'	'	'	'
Percentage of operations in Tangshan, China of owned subsidiary	'	'	'	'	60.00%	60.00%	'	'
Number of coke batteries to be closed	2	'	'	'	'	'	'	'
Profit after deduction of profit attributable to non-controlling interests	'	'	'	'	'	'	3.3	'
Book value of fixed assets	'	'	'	'	'	'	'	$2.50
Supply of export commitments	'	30.00%	'	'	'	'	'	'

Pensions_and_Postretirement_Be2

Pensions and Post-retirement Benefit Plans - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2014
	Plans
Postemployment Benefits [Abstract]	'
Number of domestic non qualified defined benefit plan	3

Pensions_and_Postretirement_Be3

Pensions and Post-retirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Postemployment Benefits [Abstract]	'	'
Service cost	$0.60	$0.90
Interest cost	2.9	2.7
Expected return on plan assets	-3.5	-3.2
Amortization of net loss	1	1.9
Net periodic benefit cost for defined benefit plans	1	2.3
Defined contribution plan expense	1.7	1.5
Other postretirement benefit plan expense	0.1	0.1
Multi-employer pension plan expense	$0.10	$0.10

Debt_Schedule_of_LongTerm_Debt

Debt - Schedule of Long-Term Debt Instruments (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Debt Instrument [Line Items]	'	'
Senior Notes	$296.70	$296.50
Total debt	340	303.1
Less short term debt and current maturities of long-term debt	0	0
Long-term debt	340	303.1
Revolving Credit Facility [Member]	'	'
Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	1.91%	'
Debt, Maturity	'2018	'
Revolving Credit Facility	15	0
Construction Loans [Member]	'	'
Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	6.24%	'
Debt, Maturity	'2018	'
Construction loans	28.3	6.6
Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	7.88%	'
Debt, Maturity	'2019	'
Long-term debt	$340	$303.10

Debt_Additional_Information_De

Debt - Additional Information (Detail)	3 Months Ended		0 Months Ended					0 Months Ended			3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Nov. 18, 2013	Mar. 31, 2014	Dec. 31, 2013	Nov. 18, 2013	Nov. 18, 2013	Nov. 18, 2013	Nov. 18, 2013	Dec. 01, 2009	Mar. 31, 2014
	Revolving Credit Facility [Member]	Revolving Credit Facility [Member]	Construction Loans [Member]	Construction Loans [Member]	Construction Loans [Member]	Construction Loans [Member]	Construction Loans [Member]	Construction Loans [Member]	Construction Loans [Member]	Senior Notes [Member]	Senior Notes [Member]
	USD ($)	USD ($)	Installment	USD ($)	USD ($)	Third Party Debt [Member]	Lender [Member]	Koppers Carbon and Chemical Company Limited [Member]	Koppers Carbon and Chemical Company Limited [Member]	USD ($)
						CNY	Committed Credit Facility [Member]	USD ($)	CNY
							CNY
Debt Instrument [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Line of credit facility, borrowing capacity	$350	'	'	'	'	'	'	'	'	'	'
Line of credit facility, commitment fees	0.3	0.3	'	'	'	'	'	'	'	'	'
Debt instrument, unused borrowing capacity	299.8	'	'	'	'	'	'	'	'	'	'
Letters of credit, amount outstanding	35.2	'	'	'	'	'	'	'	'	'	'
Percentage of owned subsidiary	'	'	'	'	'	'	'	75.00%	75.00%	'	'
Construction loan facility borrowing capacity	'	'	'	28.3	6.6	198.8	66.2	44	265	'	'
Percentage of non-controlling shareholder	'	'	25.00%	'	'	'	'	'	'	'	'
Debt maturity date	'	'	18-Nov-18	'	'	'	'	'	'	'	'
Number of installments for repayment of loans	'	'	6	'	'	'	'	'	'	'	'
Installment due frequency for repayment of loan in months	'	'	'6 months	'	'	'	'	'	'	'	'
Commencement period of debt repayment	'	'	'2016-05	'	'	'	'	'	'	'	'
Debt, Weighted Average Interest Rate	1.91%	'	'	6.24%	'	'	'	'	'	'	7.88%
Debt instrument, issuance date	'	'	'	'	'	'	'	'	'	'	1-Dec-09
Debt instrument, offering price percentage	'	'	'	'	'	'	'	'	'	98.31%	'
Debt instrument, offering value	'	'	'	'	'	'	'	'	'	294.9	'
Debt instrument, face amount	'	'	'	'	'	'	'	'	'	$300	'
Debt instrument, effective interest rate	'	'	'	'	'	'	'	'	'	'	8.13%
Debt instrument, redemption price percentage	'	'	'	'	'	'	'	'	'	'	103.94%
Frequency of interest payment on senior notes	'	'	'	'	'	'	'	'	'	'	'Interest on the Senior Notes is payable semiannually on December 1 and June 1 each year

Asset_Retirement_Obligations_S

Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligation (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract]	'	'
Balance at beginning of year	$23.20	$21.50
Accretion expense	0.5	1.2
Revision in estimated cash flows, net	0.8	6.7
Expenses incurred	-1.4	-5.6
Currency translation	0.2	-0.6
Balance at end of period	$23.30	$23.20

Deferred_Revenue_from_Extended2

Deferred Revenue from Extended Product Warranty Liabilities - Deferred Revenue from Extended Product Warranty Liabilities (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Revenue Recognition [Abstract]	'	'
Balance at beginning of year	$3.20	$3.90
Revenue earned	-0.2	-0.7
Balance at end of period	$3	$3.20

Commitments_and_Contingent_Lia2

Commitments and Contingent Liabilities - Additional Information (Detail) (USD $)

1 Months Ended

3 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

Jul. 31, 2012

Jul. 31, 2004

Mar. 31, 2014

Dec. 31, 2013

Dec. 31, 2013

Mar. 30, 2012

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Dec. 31, 2011

State

Cases

Plaintiff

site

Compensatory Damages [Member]

Punitive Damages [Member]

Pennsylvania [Member]

Pennsylvania [Member]

Arkansas [Member]

Tennessee [Member]

Australia [Member]

Australia [Member]

site

Cases

Cases

Cases

Cases

Cases

Cases

Cases

Plaintiff

Cases

Commitments And Contingent Liabilities [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of states new claims filed

'

'

3

'

'

'

'

'

'

'

'

'

'

'

Number of plaintiffs

'

'

111

'

111

'

'

'

'

'

'

'

'

'

Number of cases

'

'

61

61

61

'

61

56

57

57

3

1

'

'

Compensatory damages

'

'

'

'

'

'

'

'

'

'

$50,000

$15,000,000

'

'

Plant operation resumption period

'21 days

'

'

'

'

'

'

'

'

'

'

'

'

'

Environmental legal indemnification expense

'

7,000,000

'

'

'

'

'

'

'

'

'

'

'

'

Number of sites listed on national priorities list

'

'

1

'

'

'

'

'

'

'

'

'

'

'

Environmental remediation costs paid by others, per year

'

'

'

'

15,000,000

'

'

'

'

'

'

'

'

'

Environmental Protection Agency

'

'

80

'

'

'

'

'

'

'

'

'

'

'

Possible remedial alternatives

'

'

'

'

'

10

'

'

'

'

'

'

'

'

Remedial alternatives

'

'

'

'

'

170,000,000

'

'

'

'

'

'

'

'

Remedial alternatives

'

'

'

'

'

1,800,000,000

'

'

'

'

'

'

'

'

Environmental contingencies reserve not provided by company

'

'

1,000,000

'

'

'

'

'

'

'

'

'

'

'

Environmental remediation expense

'

'

'

'

'

'

'

'

'

'

'

'

5,900,000

1,600,000

Amount contributable by third party

'

'

'

'

'

'

'

'

'

'

'

'

'

7,500,000

Environmental remediation reserve

'

'

100,000

1,800,000

'

'

'

'

'

'

'

'

'

4,200,000

Net amount contributed by third party

'

'

'

'

'

'

'

'

'

'

'

'

2,800,000

'

Accrued liability for environmental matters, current

'

'

$8,700,000

$8,200,000

$8,200,000

'

'

'

'

'

'

'

'

'

Commitments_and_Contingent_Lia3

Commitments and Contingent Liabilities - Changes in Accrued Liability for Environmental Matters (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]	'	'
Balance at beginning of year	$11.90	$14.10
Expense	0.1	1.8
Reversal of reserves	0	-1.2
Cash expenditures	-0.1	-0.9
Currency translation	0.5	-1.9
Balance at end of period	$12.40	$11.90

Subsidiary_Guarantor_Informati4

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Additional Information (Detail) (USD $)	Dec. 01, 2009	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2013	31-May-14	Mar. 31, 2014
In Millions, unless otherwise specified	Senior Notes [Member]	Revolving Credit Facility [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]
						Revolving Credit Facility [Member]
Debt Instrument [Line Items]	'	'	'	'	'	'
Principal value of Senior Notes	$300	'	'	'	'	'
Percent-owned material domestic subsidiaries	100.00%	'	'	'	'	'
Revolving credit facility	'	350	350	'	350	'
Restricted net assets	'	'	'	'	'	154
Cash dividends paid	'	'	$7.30	$6.70	'	'

Subsidiary_Guarantor_Informati5

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Statement of Comprehensive Income (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Dec. 31, 2013
			Senior Notes [Member]	Senior Notes [Member]	Parent [Member]	Parent [Member]	Koppers Inc. [Member]	Koppers Inc. [Member]	Domestic Guarantor Subsidiaries [Member]	Domestic Guarantor Subsidiaries [Member]	Non-Guarantor Subsidiaries [Member]	Non-Guarantor Subsidiaries [Member]	Consolidating Adjustments [Member]	Consolidating Adjustments [Member]
					Senior Notes [Member]	Senior Notes [Member]	Senior Notes [Member]	Senior Notes [Member]	Senior Notes [Member]	Senior Notes [Member]	Senior Notes [Member]	Senior Notes [Member]	Senior Notes [Member]	Senior Notes [Member]
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'	'	'	'
Net sales	$331.40	$370.40	$331.40	$370.40	$0	$0	$177.60	$204.40	$10.70	$22.20	$153.90	$161.90	($10.80)	($18.10)
Cost of sales including depreciation and amortization	'	'	309.5	327.8	0	0	160.9	183	6.9	17.4	152.5	145.4	-10.8	-18
Selling, general and administrative	21.4	17.7	21.4	17.7	0.5	0.5	13.5	9.7	0.3	0.4	7.1	7.1	0	0
Operating profit	0.5	24.9	0.5	24.9	-0.5	-0.5	3.2	11.7	3.5	4.4	-5.7	9.4	0	-0.1
Other income (expense)	0.2	0.5	0.2	0.5	0	0	0	0.1	0.9	1.1	0.3	0.4	-1	-1.1
Equity income of subsidiaries	'	'	0	0	2.5	11.4	2.3	11.1	-8.2	5.6	0	0	3.4	-28.1
Interest expense (income)	6.8	6.9	6.8	6.9	0	0.1	6.8	6.8	0	0	1	1.1	-1	-1.1
Income taxes	-6	7.1	-6	7.1	-0.2	-0.2	-3.7	4.7	-6	0.1	3.9	2.5	0	0
(Loss) income from continuing operations	-0.1	11.4	-0.1	11.4	2.2	11	2.4	11.4	2.2	11	-10.3	6.2	3.4	-28.2
Discontinued operations	0	0.1	'	0.1	'	0	'	0	'	0	'	0.1	'	0
Noncontrolling interests	-2.3	0.5	-2.3	0.5	0	0	0	0	0	0	-2.3	0.5	0	0
Net income attributable to Koppers	2.2	11	2.2	11	2.2	11	2.4	11.4	2.2	11	-8	5.8	3.4	-28.2
Comprehensive income attributable to Koppers	$5.30	$9.30	$5.30	$9.30	$5.30	$9.30	$5.60	$9.50	$4.90	$8.10	$0.20	($3.60)	($10.70)	($14)

Subsidiary_Guarantor_Informati6

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Balance Sheet (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets	'	'	'	'
Cash and cash equivalents	$54.70	$82.20	$56.70	$66.70
Receivables, net	157.3	157.9	'	'
Inventories, net	193.2	168.8	'	'
Deferred tax assets	12.4	10	'	'
Other current assets	31.4	35.7	'	'
Total current assets	469.6	473.1	'	'
Equity investments	6.7	6.6	'	'
Property, plant and equipment, net	202.5	197	'	'
Goodwill	75	72.7	'	'
Deferred tax assets	14.7	9.3	'	'
Other noncurrent assets	32.7	26.2	'	'
Total assets	801.2	784.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	91.8	107.6	'	'
Accrued liabilities	83.4	82.4	'	'
Total current liabilities	180.3	195.1	'	'
Long-term debt	340	303.1	'	'
Total liabilities	614.8	595.1	'	'
Koppers shareholders' equity	169.2	169.8	'	'
Noncontrolling interests	17.2	20	'	'
Total liabilities and equity	801.2	784.9	'	'
Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	54.7	82.2	56.7	66.7
Receivables, net	168.4	166.9	'	'
Affiliated receivables	0	0	'	'
Inventories, net	193.2	168.8	'	'
Deferred tax assets	12.4	10	'	'
Other current assets	40.9	45.2	'	'
Total current assets	469.6	473.1	'	'
Equity investments	6.7	6.6	'	'
Property, plant and equipment, net	202.5	197	'	'
Goodwill	75	72.7	'	'
Deferred tax assets	14.7	9.3	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	32.7	26.2	'	'
Total assets	801.2	784.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	91.8	107.6	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	88.5	87.5	'	'
Total current liabilities	180.3	195.1	'	'
Long-term debt	340	303.1	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	94.5	96.9	'	'
Total liabilities	614.8	595.1	'	'
Koppers shareholders' equity	169.2	169.8	'	'
Noncontrolling interests	17.2	20	'	'
Total liabilities and equity	801.2	784.9	'	'
Parent [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	0	0.2	'	'
Inventories, net	0	0	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	0	0.2	'	'
Equity investments	174.2	174.7	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	0	0	'	'
Total assets	174.2	174.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0.1	0	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	4.9	5.1	'	'
Total current liabilities	5	5.1	'	'
Long-term debt	0	0	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	5	5.1	'	'
Koppers shareholders' equity	169.2	169.8	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	174.2	174.9	'	'
Koppers Inc. [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	29.9	2.7	4.8
Receivables, net	84.5	75.6	'	'
Affiliated receivables	5.3	1.1	'	'
Inventories, net	94.5	86.1	'	'
Deferred tax assets	7.9	7.9	'	'
Other current assets	5.8	7.3	'	'
Total current assets	198	207.9	'	'
Equity investments	338.5	333.5	'	'
Property, plant and equipment, net	110.8	112.2	'	'
Goodwill	39.8	39.8	'	'
Deferred tax assets	3.8	2.4	'	'
Affiliated loan receivables	36.8	8.5	'	'
Other noncurrent assets	14.4	15	'	'
Total assets	742.1	719.3	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	45.9	48.3	'	'
Affiliated payables	9.7	1.9	'	'
Accrued liabilities	30.6	27.8	'	'
Total current liabilities	86.2	78	'	'
Long-term debt	311.7	296.5	'	'
Affiliated debt	111.9	109.5	'	'
Other long-term liabilities	63.3	67.6	'	'
Total liabilities	573.1	551.6	'	'
Koppers shareholders' equity	169	167.7	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	742.1	719.3	'	'
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0.1	0.1	0
Receivables, net	3	9.3	'	'
Affiliated receivables	6.3	3.9	'	'
Inventories, net	0	0	'	'
Deferred tax assets	3.9	1.5	'	'
Other current assets	0.5	0.6	'	'
Total current assets	13.7	15.4	'	'
Equity investments	185.2	182.9	'	'
Property, plant and equipment, net	0.1	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	2.3	-1.4	'	'
Affiliated loan receivables	146.1	123.8	'	'
Other noncurrent assets	0	0	'	'
Total assets	347.4	320.7	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	2.6	6.7	'	'
Affiliated payables	1.7	4	'	'
Accrued liabilities	0.3	0.5	'	'
Total current liabilities	4.6	11.2	'	'
Long-term debt	0	0	'	'
Affiliated debt	36.8	8.5	'	'
Other long-term liabilities	2.6	2.5	'	'
Total liabilities	44	22.2	'	'
Koppers shareholders' equity	303.4	298.5	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	347.4	320.7	'	'
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	54.7	52.2	53.9	61.9
Receivables, net	80.9	82	'	'
Affiliated receivables	4.8	2.3	'	'
Inventories, net	98.9	82.9	'	'
Deferred tax assets	0.6	0.6	'	'
Other current assets	34.6	37.3	'	'
Total current assets	274.5	257.3	'	'
Equity investments	4.8	4.6	'	'
Property, plant and equipment, net	91.6	84.8	'	'
Goodwill	35.2	32.9	'	'
Deferred tax assets	8.6	8.3	'	'
Affiliated loan receivables	40.5	40.9	'	'
Other noncurrent assets	18.3	11.2	'	'
Total assets	473.5	440	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	43.2	52.6	'	'
Affiliated payables	10.2	8.6	'	'
Accrued liabilities	52.7	54.1	'	'
Total current liabilities	106.1	115.3	'	'
Long-term debt	28.3	6.6	'	'
Affiliated debt	74.7	55.2	'	'
Other long-term liabilities	28.6	26.8	'	'
Total liabilities	237.7	203.9	'	'
Koppers shareholders' equity	218.6	216.1	'	'
Noncontrolling interests	17.2	20	'	'
Total liabilities and equity	473.5	440	'	'
Consolidating Adjustments [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	-16.4	-7.5	'	'
Inventories, net	-0.2	-0.2	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	-16.6	-7.7	'	'
Equity investments	-696	-689.1	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	-223.4	-173.2	'	'
Other noncurrent assets	0	0	'	'
Total assets	-936	-870	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0	0	'	'
Affiliated payables	-21.6	-14.5	'	'
Accrued liabilities	0	0	'	'
Total current liabilities	-21.6	-14.5	'	'
Long-term debt	0	0	'	'
Affiliated debt	-223.4	-173.2	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	-245	-187.7	'	'
Koppers shareholders' equity	-691	-682.3	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	($936)	($870)	'	'

Subsidiary_Guarantor_Informati7

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Statement of Cash Flows (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	($13.70)	$5.70
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-14.8	-6.4
Net cash proceeds (payments) from divestitures and asset sales	0	0.2
Net cash provided by (used in) investing activities	-44.4	-6.2
Cash provided by (used in) financing activities:	'	'
Deferred financing costs	0	-1.1
Dividends paid	-5	-5
Net cash provided by (used in) financing activities	30.2	-7.5
Effect of exchange rates on cash	0.4	-2
Net increase (decrease) in cash and cash equivalents	-27.5	-10
Cash and cash equivalents at beginning of year	82.2	66.7
Cash and cash equivalents at end of period	54.7	56.7
Senior Notes [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	-13.7	5.7
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-44.4	-6.4
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0.2
Net cash provided by (used in) investing activities	-44.4	-6.2
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	37.2	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	'	-1.1
Dividends paid	-5	-5
Stock issued (repurchased)	-2	-1.4
Net cash provided by (used in) financing activities	30.2	-7.5
Effect of exchange rates on cash	0.4	-2
Net increase (decrease) in cash and cash equivalents	-27.5	-10
Cash and cash equivalents at beginning of year	82.2	66.7
Cash and cash equivalents at end of period	54.7	56.7
Parent [Member] | Senior Notes [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	7	6.4
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	0	0
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	0	0
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	'	0
Dividends paid	-5	-5
Stock issued (repurchased)	-2	-1.4
Net cash provided by (used in) financing activities	-7	-6.4
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	0	0
Koppers Inc. [Member] | Senior Notes [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	-8	5.4
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-3.2	-3.5
(Loans to) repayments from affiliates	-28.5	0.1
Net cash proceeds (payments) from divestitures and asset sales	0	0.1
Net cash provided by (used in) investing activities	-31.7	-3.3
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	15	'
Borrowings (repayments) of affiliated debt	2.1	3.6
Deferred financing costs	'	-1.1
Dividends paid	-7.3	-6.7
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	9.8	-4.2
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	-29.9	-2.1
Cash and cash equivalents at beginning of year	29.9	4.8
Cash and cash equivalents at end of period	0	2.7
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	5.8	4.1
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-14.9	0
(Loans to) repayments from affiliates	-19.5	-3.9
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	-34.4	-3.9
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	28.5	-0.1
Deferred financing costs	'	0
Dividends paid	0	0
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	28.5	-0.1
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	-0.1	0.1
Cash and cash equivalents at beginning of year	0.1	0
Cash and cash equivalents at end of period	0	0.1
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	-6.7	-0.4
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-41.1	-2.9
(Loans to) repayments from affiliates	0.4	0.3
Net cash proceeds (payments) from divestitures and asset sales	0	0.1
Net cash provided by (used in) investing activities	-40.7	-2.5
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	22.2	'
Borrowings (repayments) of affiliated debt	17	0
Deferred financing costs	'	0
Dividends paid	-4.5	-3.1
Stock issued (repurchased)	14.8	0
Net cash provided by (used in) financing activities	49.5	-3.1
Effect of exchange rates on cash	0.4	-2
Net increase (decrease) in cash and cash equivalents	2.5	-8
Cash and cash equivalents at beginning of year	52.2	61.9
Cash and cash equivalents at end of period	54.7	53.9
Consolidating Adjustments [Member] | Senior Notes [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	-11.8	-9.8
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	14.8	0
(Loans to) repayments from affiliates	47.6	3.5
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	62.4	3.5
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	-47.6	-3.5
Deferred financing costs	'	0
Dividends paid	11.8	9.8
Stock issued (repurchased)	-14.8	0
Net cash provided by (used in) financing activities	-50.6	6.3
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	$0	$0

Subsidiary_Guarantor_Informati8

Subsidiary Guarantor Information for Shelf Registration - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	31-May-14
Subsidiary Guarantor Information for Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'
Cash dividends paid	$7.30	$6.70	'
Subsidiary Guarantor Information for Shelf Registration [Member] | Revolving Credit Facility [Member]	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'
Restricted net assets	154	'	'
Payment Guarantee by Subsidiaries for Senior Notes [Member]	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'
Revolving credit facility	350	'	350
Cash dividends paid	$7.30	$6.70	'
Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'
Percent owned subsidiaries	100.00%	'	'

Subsidiary_Guarantor_Informati9

Subsidiary Guarantor Information for Shelf Registration - Condensed Consolidating Statement of Comprehensive Income (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'
Net sales	$331.40	$370.40
Selling, general and administrative	21.4	17.7
Operating profit (loss)	0.5	24.9
Other income (expense)	0.2	0.5
Interest expense (income)	6.8	6.9
Income taxes	-6	7.1
Income from continuing operations	-0.1	11.4
Discontinued operations	0	0.1
Noncontrolling interests	-2.3	0.5
Net income attributable to Koppers	2.2	11
Comprehensive income attributable to Koppers	5.3	9.3
Shelf Registration [Member]	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'
Net sales	331.4	370.4
Cost of sales including depreciation and amortization	309.5	327.8
Selling, general and administrative	21.4	17.7
Operating profit (loss)	0.5	24.9
Other income (expense)	0.2	0.5
Equity income of subsidiaries	0	0
Interest expense (income)	6.8	6.9
Income taxes	-6	7.1
Income from continuing operations	-0.1	11.4
Discontinued operations	0	0.1
Noncontrolling interests	-2.3	0.5
Net income attributable to Koppers	2.2	11
Comprehensive income attributable to Koppers	5.3	9.3
Shelf Registration [Member] | Parent [Member]	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'
Net sales	0	0
Cost of sales including depreciation and amortization	0	0
Selling, general and administrative	0.5	0.5
Operating profit (loss)	-0.5	-0.5
Other income (expense)	0	0
Equity income of subsidiaries	2.5	11.4
Interest expense (income)	0	0.1
Income taxes	-0.2	-0.2
Income from continuing operations	2.2	11
Discontinued operations	0	0
Noncontrolling interests	0	0
Net income attributable to Koppers	2.2	11
Comprehensive income attributable to Koppers	5.3	9.3
Shelf Registration [Member] | Koppers Inc. [Member]	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'
Net sales	177.6	204.4
Cost of sales including depreciation and amortization	160.9	183
Selling, general and administrative	13.5	9.7
Operating profit (loss)	3.2	11.7
Other income (expense)	0	0.1
Equity income of subsidiaries	2.3	11.1
Interest expense (income)	6.8	6.8
Income taxes	-3.7	4.7
Income from continuing operations	2.4	11.4
Discontinued operations	0	0
Noncontrolling interests	0	0
Net income attributable to Koppers	2.4	11.4
Comprehensive income attributable to Koppers	5.6	9.6
Shelf Registration [Member] | Domestic Guarantor Subsidiaries [Member]	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'
Net sales	10.7	22.2
Cost of sales including depreciation and amortization	6.9	17.4
Selling, general and administrative	0.3	0.4
Operating profit (loss)	3.5	4.4
Other income (expense)	0.9	1.1
Equity income of subsidiaries	-8.2	5.6
Interest expense (income)	0	0
Income taxes	-6	0.1
Income from continuing operations	2.2	11
Discontinued operations	0	0
Noncontrolling interests	0	0
Net income attributable to Koppers	2.2	11
Comprehensive income attributable to Koppers	4.9	8.2
Shelf Registration [Member] | Foreign Guarantor Subsidiaries [Member]	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'
Net sales	113.1	121.5
Cost of sales including depreciation and amortization	108.1	107.7
Selling, general and administrative	5.8	6
Operating profit (loss)	-0.8	7.8
Other income (expense)	0	0
Equity income of subsidiaries	-3.4	0.5
Interest expense (income)	0.6	0.8
Income taxes	3.3	2
Income from continuing operations	-8.1	5.5
Discontinued operations	0	0.1
Noncontrolling interests	0	0
Net income attributable to Koppers	-8.1	5.6
Comprehensive income attributable to Koppers	-6.1	1.8
Shelf Registration [Member] | Non-Guarantor Subsidiaries [Member]	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'
Net sales	40.8	40.7
Cost of sales including depreciation and amortization	44.4	38
Selling, general and administrative	1.3	1.1
Operating profit (loss)	-4.9	1.6
Other income (expense)	0.3	0.4
Equity income of subsidiaries	0	0
Interest expense (income)	0.4	0.3
Income taxes	0.6	0.5
Income from continuing operations	-5.6	1.2
Discontinued operations	0	0
Noncontrolling interests	-2.3	0.5
Net income attributable to Koppers	-3.3	0.7
Comprehensive income attributable to Koppers	-0.9	0.1
Consolidating Adjustments [Member] | Shelf Registration [Member]	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'
Net sales	-10.8	-18.4
Cost of sales including depreciation and amortization	-10.8	-18.3
Selling, general and administrative	0	0
Operating profit (loss)	0	-0.1
Other income (expense)	-1	-1.1
Equity income of subsidiaries	6.8	-28.6
Interest expense (income)	-1	-1.1
Income taxes	0	0
Income from continuing operations	6.8	-28.7
Discontinued operations	0	0
Noncontrolling interests	0	0
Net income attributable to Koppers	6.8	-28.7
Comprehensive income attributable to Koppers	($3.50)	($19.70)

Recovered_Sheet1

Subsidiary Guarantor Information for Shelf Registration - Condensed Consolidating Balance Sheet (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets	'	'	'	'
Cash and cash equivalents	$54.70	$82.20	$56.70	$66.70
Receivables, net	157.3	157.9	'	'
Inventories, net	193.2	168.8	'	'
Deferred tax assets	12.4	10	'	'
Other current assets	31.4	35.7	'	'
Total current assets	469.6	473.1	'	'
Equity investments	6.7	6.6	'	'
Property, plant and equipment, net	202.5	197	'	'
Goodwill	75	72.7	'	'
Deferred tax assets	14.7	9.3	'	'
Other noncurrent assets	32.7	26.2	'	'
Total assets	801.2	784.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	91.8	107.6	'	'
Accrued liabilities	83.4	82.4	'	'
Total current liabilities	180.3	195.1	'	'
Long-term debt	340	303.1	'	'
Total liabilities	614.8	595.1	'	'
Koppers shareholders' equity	169.2	169.8	'	'
Noncontrolling interests	17.2	20	'	'
Total liabilities and equity	801.2	784.9	'	'
Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	54.7	82.2	56.7	66.7
Receivables, net	168.4	166.9	'	'
Affiliated receivables	0	0	'	'
Inventories, net	193.2	168.8	'	'
Deferred tax assets	12.4	10	'	'
Other current assets	40.9	45.2	'	'
Total current assets	469.6	473.1	'	'
Equity investments	6.7	6.6	'	'
Property, plant and equipment, net	202.5	197	'	'
Goodwill	75	72.7	'	'
Deferred tax assets	14.7	9.3	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	32.7	26.2	'	'
Total assets	801.2	784.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	91.8	107.6	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	88.5	87.5	'	'
Total current liabilities	180.3	195.1	'	'
Long-term debt	340	303.1	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	94.5	96.9	'	'
Total liabilities	614.8	595.1	'	'
Koppers shareholders' equity	169.2	169.8	'	'
Noncontrolling interests	17.2	20	'	'
Total liabilities and equity	801.2	784.9	'	'
Shelf Registration [Member] | Parent [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	0	0.2	'	'
Inventories, net	0	0	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	0	0.2	'	'
Equity investments	174.2	174.7	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	0	0	'	'
Total assets	174.2	174.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0.1	0	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	4.9	5.1	'	'
Total current liabilities	5	5.1	'	'
Long-term debt	0	0	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	5	5.1	'	'
Koppers shareholders' equity	169.2	169.8	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	174.2	174.9	'	'
Shelf Registration [Member] | Koppers Inc. [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	29.9	2.7	4.8
Receivables, net	84.5	75.6	'	'
Affiliated receivables	5.3	1.1	'	'
Inventories, net	94.5	86.1	'	'
Deferred tax assets	7.9	7.9	'	'
Other current assets	5.8	7.3	'	'
Total current assets	198	207.9	'	'
Equity investments	338.5	333.5	'	'
Property, plant and equipment, net	110.8	112.2	'	'
Goodwill	39.8	39.8	'	'
Deferred tax assets	3.8	2.4	'	'
Affiliated loan receivables	36.8	8.5	'	'
Other noncurrent assets	14.4	15	'	'
Total assets	742.1	719.3	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	45.9	48.3	'	'
Affiliated payables	9.7	1.9	'	'
Accrued liabilities	30.6	27.8	'	'
Total current liabilities	86.2	78	'	'
Long-term debt	311.7	296.5	'	'
Affiliated debt	111.9	109.5	'	'
Other long-term liabilities	63.3	67.6	'	'
Total liabilities	573.1	551.6	'	'
Koppers shareholders' equity	169	167.7	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	742.1	719.3	'	'
Shelf Registration [Member] | Domestic Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0.1	0.1	0
Receivables, net	3	9.3	'	'
Affiliated receivables	6.3	3.9	'	'
Inventories, net	0	0	'	'
Deferred tax assets	3.9	1.5	'	'
Other current assets	0.5	0.6	'	'
Total current assets	13.7	15.4	'	'
Equity investments	185.2	182.9	'	'
Property, plant and equipment, net	0.1	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	2.3	-1.4	'	'
Affiliated loan receivables	146.1	123.8	'	'
Other noncurrent assets	0	0	'	'
Total assets	347.4	320.7	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	2.6	6.7	'	'
Affiliated payables	1.7	4	'	'
Accrued liabilities	0.3	0.5	'	'
Total current liabilities	4.6	11.2	'	'
Long-term debt	0	0	'	'
Affiliated debt	36.8	8.5	'	'
Other long-term liabilities	2.6	2.5	'	'
Total liabilities	44	22.2	'	'
Koppers shareholders' equity	303.4	298.5	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	347.4	320.7	'	'
Shelf Registration [Member] | Foreign Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	41.8	43.5	37.9	40.7
Receivables, net	51.5	55.5	'	'
Affiliated receivables	3.6	0.8	'	'
Inventories, net	75	75.2	'	'
Deferred tax assets	0	0	'	'
Other current assets	16.8	17.5	'	'
Total current assets	188.7	192.5	'	'
Equity investments	46.2	50.5	'	'
Property, plant and equipment, net	39.3	38.1	'	'
Goodwill	32.4	31.5	'	'
Deferred tax assets	5.6	5.5	'	'
Affiliated loan receivables	0.1	0.1	'	'
Other noncurrent assets	10.2	9.9	'	'
Total assets	322.5	328.1	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	32.8	40.6	'	'
Affiliated payables	1.2	0.4	'	'
Accrued liabilities	41.8	31.4	'	'
Total current liabilities	75.8	72.4	'	'
Long-term debt	0	0	'	'
Affiliated debt	57.6	55.2	'	'
Other long-term liabilities	20.4	19.6	'	'
Total liabilities	153.8	147.2	'	'
Koppers shareholders' equity	168.7	180.9	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	322.5	328.1	'	'
Shelf Registration [Member] | Non-Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	12.9	8.7	16	21.2
Receivables, net	29.4	26.5	'	'
Affiliated receivables	1.3	1.6	'	'
Inventories, net	23.9	7.7	'	'
Deferred tax assets	0.6	0.6	'	'
Other current assets	17.8	19.8	'	'
Total current assets	85.9	64.9	'	'
Equity investments	4.8	4.5	'	'
Property, plant and equipment, net	52.3	46.7	'	'
Goodwill	2.8	1.4	'	'
Deferred tax assets	3	2.8	'	'
Affiliated loan receivables	40.4	40.8	'	'
Other noncurrent assets	8.1	1.3	'	'
Total assets	197.3	162.4	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	10.4	12	'	'
Affiliated payables	9	8.4	'	'
Accrued liabilities	10.9	22.7	'	'
Total current liabilities	30.3	43.1	'	'
Long-term debt	28.3	6.6	'	'
Affiliated debt	17.1	0	'	'
Other long-term liabilities	8.2	7.2	'	'
Total liabilities	83.9	56.9	'	'
Koppers shareholders' equity	96.2	85.5	'	'
Noncontrolling interests	17.2	20	'	'
Total liabilities and equity	197.3	162.4	'	'
Consolidating Adjustments [Member] | Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	-16.5	-7.6	'	'
Inventories, net	-0.2	-0.2	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	-16.7	-7.8	'	'
Equity investments	-742.2	-739.5	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	-223.4	-173.2	'	'
Other noncurrent assets	0	0	'	'
Total assets	-982.3	-920.5	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0	0	'	'
Affiliated payables	-21.6	-14.7	'	'
Accrued liabilities	0	0	'	'
Total current liabilities	-21.6	-14.7	'	'
Long-term debt	0	0	'	'
Affiliated debt	-223.4	-173.2	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	-245	-187.9	'	'
Koppers shareholders' equity	-737.3	-732.6	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	($982.30)	($920.50)	'	'

Recovered_Sheet2

Subsidiary Guarantor Information for Shelf Registration - Condensed Consolidating Statement of Cash Flows (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	($13.70)	$5.70
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-14.8	-6.4
Net cash proceeds (payments) from divestitures and asset sales	0	0.2
Net cash provided by (used in) investing activities	-44.4	-6.2
Cash provided by (used in) financing activities:	'	'
Deferred financing costs	0	-1.1
Dividends paid	-5	-5
Net cash provided by (used in) financing activities	30.2	-7.5
Effect of exchange rates on cash	0.4	-2
Net increase (decrease) in cash and cash equivalents	-27.5	-10
Cash and cash equivalents at beginning of year	82.2	66.7
Cash and cash equivalents at end of period	54.7	56.7
Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	-13.7	5.7
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-44.4	-6.4
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0.2
Net cash provided by (used in) investing activities	-44.4	-6.2
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	37.2	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	'	-1.1
Dividends paid	-5	-5
Stock issued (repurchased)	-2	-1.4
Net cash provided by (used in) financing activities	30.2	-7.5
Effect of exchange rates on cash	0.4	-2
Net increase (decrease) in cash and cash equivalents	-27.5	-10
Cash and cash equivalents at beginning of year	82.2	66.7
Cash and cash equivalents at end of period	54.7	56.7
Shelf Registration [Member] | Parent [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	7	6.4
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	0	0
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	0	0
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	'	0
Dividends paid	-5	-5
Stock issued (repurchased)	-2	-1.4
Net cash provided by (used in) financing activities	-7	-6.4
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	0	0
Shelf Registration [Member] | Koppers Inc. [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	-8	5.4
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-3.2	-3.5
(Loans to) repayments from affiliates	-28.5	0.1
Net cash proceeds (payments) from divestitures and asset sales	0	0.1
Net cash provided by (used in) investing activities	-31.7	-3.3
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	15	'
Borrowings (repayments) of affiliated debt	2.1	3.6
Deferred financing costs	'	-1.1
Dividends paid	-7.3	-6.7
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	9.8	-4.2
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	-29.9	-2.1
Cash and cash equivalents at beginning of year	29.9	4.8
Cash and cash equivalents at end of period	0	2.7
Shelf Registration [Member] | Domestic Guarantor Subsidiaries [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	5.8	4.1
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-14.9	0
(Loans to) repayments from affiliates	-19.5	-3.9
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	-34.4	-3.9
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	28.5	-0.1
Deferred financing costs	'	0
Dividends paid	0	0
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	28.5	-0.1
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	-0.1	0.1
Cash and cash equivalents at beginning of year	0.1	0
Cash and cash equivalents at end of period	0	0.1
Shelf Registration [Member] | Foreign Guarantor Subsidiaries [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	4.8	3.2
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-2.7	-1
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0.1
Net cash provided by (used in) investing activities	-2.7	-0.9
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	'	0
Dividends paid	-4.5	-3.1
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	-4.5	-3.1
Effect of exchange rates on cash	0.7	-2
Net increase (decrease) in cash and cash equivalents	-1.7	-2.8
Cash and cash equivalents at beginning of year	43.5	40.7
Cash and cash equivalents at end of period	41.8	37.9
Shelf Registration [Member] | Non-Guarantor Subsidiaries [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	-11.5	-3.6
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-38.4	-1.9
(Loans to) repayments from affiliates	0.4	0.3
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	-38	-1.6
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	22.2	'
Borrowings (repayments) of affiliated debt	17	0
Deferred financing costs	'	0
Dividends paid	0	0
Stock issued (repurchased)	14.8	0
Net cash provided by (used in) financing activities	54	0
Effect of exchange rates on cash	-0.3	0
Net increase (decrease) in cash and cash equivalents	4.2	-5.2
Cash and cash equivalents at beginning of year	8.7	21.2
Cash and cash equivalents at end of period	12.9	16
Consolidating Adjustments [Member] | Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	-11.8	-9.8
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	14.8	0
(Loans to) repayments from affiliates	47.6	3.5
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	62.4	3.5
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	-47.6	-3.5
Deferred financing costs	'	0
Dividends paid	11.8	9.8
Stock issued (repurchased)	-14.8	0
Net cash provided by (used in) financing activities	-50.6	6.3
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	$0	$0

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Related Party Transactions [Abstract]	'	'
Loan to related party	$9.50	$9.50
Ownership percentage	30.00%	'
Loan repayable date	'November 2014	'