Koppers (KOP) 10-Q 7 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 31, 2013
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-13	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'
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	'	20,331,998

Condensed_Consolidated_Stateme

Condensed Consolidated Statement of Comprehensive Income (USD $)	3 Months Ended		9 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]	'	'	'	'
Net sales	$395.20	$387.90	$1,136.50	$1,180.10
Cost of sales (excluding items below)	330.6	331.4	970	1,003.20
Depreciation and amortization	7.2	6.7	21.8	21.1
Selling, general and administrative expenses	18.3	19	52.2	55.1
Operating profit (loss)	39.1	30.8	92.5	100.7
Other income	1.3	0.6	2.8	1.7
Interest expense	6.7	6.9	20.2	20.8
Income before income taxes	33.7	24.5	75.1	81.6
Income taxes	14.1	8.3	29.3	28.5
Income from continuing operations	19.6	16.2	45.8	53.1
Loss from discontinued operations, net of tax benefit of $0.1, $0.0, $0.1 and $0.2	-0.1	0	-0.1	-0.1
Net income	19.5	16.2	45.7	53
Net income attributable to noncontrolling interests	0.4	0.2	1.2	1
Net income attributable to Koppers	19.1	16	44.5	52
Basic -	'	'	'	'
Continuing operations	$0.93	$0.77	$2.16	$2.52
Discontinued operations	$0	$0	$0	($0.01)
Earnings per basic common share	$0.93	$0.77	$2.16	$2.51
Diluted -	'	'	'	'
Continuing operations	$0.92	$0.77	$2.13	$2.50
Discontinued operations	$0	$0	$0	($0.01)
Earnings per diluted common share	$0.92	$0.77	$2.13	$2.49
Comprehensive income	26.6	25.3	42.3	60.8
Comprehensive income attributable to noncontrolling interests	0.8	0.3	1.5	1
Comprehensive income attributable to Koppers	$25.80	$25	$40.80	$59.80
Weighted average shares outstanding (in thousands):	'	'	'	'
Basic	20,577	20,694	20,657	20,709
Diluted	20,801	20,900	20,887	20,940
Dividends declared per common share	$0.25	$0.24	$0.75	$0.72

Condensed_Consolidated_Stateme1

Condensed Consolidated Statement of Comprehensive Income (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]	'	'	'	'
Loss from discontinued operations, net of tax benefit	$0.10	$0	$0.10	$0.20

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheet (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets	'	'
Cash and cash equivalents	$72.40	$66.70
Restricted cash	1.5	0
Accounts receivable, net of allowance of $3.5 and $3.7	182.1	162.7
Inventories, net	166.4	195.8
Deferred tax assets	14.7	15.1
Loan to related party	9.5	9.5
Other current assets	25.6	31.4
Total current assets	472.2	481.2
Equity in non-consolidated investments	6.2	5.8
Property, plant and equipment, net	169.4	161.1
Goodwill	73.4	75.6
Deferred tax assets	12.6	27.2
Other assets	27.3	29.1
Total assets	761.1	780
Liabilities	'	'
Accounts payable	94.9	103.5
Accrued liabilities	66.3	72.1
Dividends payable	5.8	5.6
Total current liabilities	167	181.2
Long-term debt	296.4	296.1
Accrued postretirement benefits	71.5	89.9
Other long-term liabilities	41.5	44.7
Total liabilities	576.4	611.9
Commitments and contingent liabilities (Note 16)	'	'
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; 21,722,492 and 21,585,129 shares issued	0.2	0.2
Additional paid-in capital	158.8	153.3
Retained earnings	80.6	52
Accumulated other comprehensive loss	-25.8	-22
Treasury stock, at cost, 1,390,494 and 951,026 shares	-50.4	-32.9
Total Koppers shareholders' equity	163.4	150.6
Noncontrolling interests	21.3	17.5
Total equity	184.7	168.1
Total liabilities and equity	$761.10	$780

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheet (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, except Share data, unless otherwise specified
Statement Of Financial Position [Abstract]	'	'
Accounts receivable, allowance	$3.50	$3.70
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	21,722,492	21,585,129
Treasury stock, shares	1,390,494	951,026

Condensed_Consolidated_Stateme2

Condensed Consolidated Statement of Cash Flows (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash provided by (used in) operating activities:	'	'
Net income	$45.70	$53
Adjustments to reconcile net cash provided by operating activities:	'	'
Depreciation and amortization	21.8	21.1
Deferred income taxes	11.1	7.7
Equity income, net of dividends received	-0.4	-0.9
Gain on sale of assets	-1.9	-0.2
Change in other liabilities	-14.2	-8.3
Non-cash interest expense	1.2	1.2
Stock-based compensation	4.7	5.1
Other	0.6	-0.2
(Increase) decrease in working capital:	'	'
Accounts receivable	-17.9	-11.4
Inventories	25.5	-29.9
Accounts payable	-8	6.7
Accrued liabilities and other working capital	-2.6	10.6
Cash provided by (used in) operating activities	65.6	54.5
Cash provided by (used in) investing activities:	'	'
Capital expenditures	-29.4	-15.8
Net cash proceeds from divestitures and asset sales	2.4	0.7
Net cash provided by (used in) investing activities	-27	-15.1
Cash provided by (used in) financing activities:	'	'
Borrowings of revolving credit	97.9	225.9
Repayments of revolving credit	-97.9	-230.9
Issuances of Common Stock	0.2	0.8
Repurchases of Common Stock	-17.5	-8.2
Proceeds from issuance of noncontrolling interest	2.3	0
Payment of deferred financing costs	-1.2	-0.1
Dividends paid	-15.3	-14.5
Net cash provided by (used in) financing activities	-31.5	-27
Effect of exchange rate changes on cash	-1.4	2.4
Net increase in cash and cash equivalents	5.7	14.8
Cash and cash equivalents at beginning of year	66.7	54.1
Cash and cash equivalents at end of period	$72.40	$68.90

Basis_of_Presentation_and_New_

Basis of Presentation and New Accounting Standards	9 Months Ended
	Sep. 30, 2013
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, 2012 has been summarized from the audited balance sheet contained in the Annual Report on Form 10-K for the year ended December 31, 2012.
	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, 2012.
	The Financial Accounting Standards Board issued Accounting Standards Update No. 2013-02, Reporting of Amounts Reclassified Out of Other Comprehensive Income (ASU 2013-2). The amendments in ASU 2013-02 require entities to provide additional disclosures regarding amounts that have been reclassified out of other comprehensive income during the periods presented either on the face of the financial statements or in the notes to the financial statements. ASU 2013-02 is effective for interim and annual periods beginning after December 15, 2012. We have elected to present such information in the notes to the financial statements (see Note 5).

Dividends

Dividends	9 Months Ended
	Sep. 30, 2013
Text Block [Abstract]	'
Dividends	'
	2. Dividends
	On November 6, 2013, the Company’s board of directors declared a quarterly dividend of 25 cents per common share, payable on January 6, 2014 to shareholders of record as of November 18, 2013.

Discontinued_Operations

Discontinued Operations	9 Months Ended
	Sep. 30, 2013
Discontinued Operations And Disposal Groups [Abstract]	'
Discontinued Operations	'
	3. Discontinued operations
	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.
	Details of the restructuring activities and related reserves are as follows:
		Severance and			Environmental			Inventory			Site			Other			Total
		employee benefits			remediation			writedowns			demolition
	(Dollars in millions)
	Reserve at December 31, 2011	$	1.8		$	6.7		$	0		$	6.2		$	1.2		$	15.9
	Charges		0.1			0			0.4			0			0			0.5
	Costs charged against assets		0			0			(0.4	)		0			0			(0.4	)
	Reversal of accrued charges		0			0			0			0			(0.6	)		(0.6	)
	Cash expenditures		(1.7	)		(0.1	)		0			(0.4	)		(0.5	)		(2.7	)
	Currency translation		0			0.1			0			0.1			0			0.2
	Reserve at December 31, 2012	$	0.2		$	6.7		$	0		$	5.9		$	0.1		$	12.9
	Reversal of accrued charges		(0.1	)		0			0			(0.3	)		0			(0.4	)
	Cash expenditures		0			(0.1	)		0			(1.5	)		0			(1.6	)
	Currency translation		0			(0.7	)		0			(0.5	)		0			(1.2	)
	Reserve at September 30, 2013	$	0.1		$	5.9		$	0		$	3.6		$	0.1		$	9.7
	Net sales and operating profit from discontinued operations for the three months and nine months ended September 30, 2013 and 2012 consist of the following amounts:
		Three Months						Nine Months
		Ended September 30,						Ended September 30,
		2013			2012			2013			2012
	Net sales	$	0		$	0.3		$	0		$	5.7
	Operating loss		(0.1	)		(0.1	)		(0.2	)		(0.3	)

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	4. Fair Value Measurements
	Carrying amounts and the related estimated fair values of the Company’s financial instruments as of September 30, 2013 and December 31, 2012 are as follows:
			September 30, 2013				December 31, 2012
			Fair Value		Carrying		Fair Value		Carrying
					Value				Value
	(Dollars in millions)
	Financial assets:
	Cash and cash equivalents, including restricted cash		$	73.9	$	73.9	$	66.7	$	66.7
	Investments and other assets(a)			1.4		1.4		1.4		1.4
	Financial liabilities:
	Long-term debt		$	325.3	$	296.4	$	331.1	$	296.1
	(a)	Excludes equity method investments.
	Cash and cash equivalents, including restricted cash – 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 approximate carrying value due to the variable rate nature of these instruments.

Comprehensive_Income_and_Equit

Comprehensive Income and Equity	9 Months Ended
	Sep. 30, 2013
Equity [Abstract]	'
Comprehensive Income and Equity	'
	5. Comprehensive Income and Equity
	Total comprehensive income for the three and nine months ended September 30, 2013 and 2012 is summarized in the table below:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
	(Dollars in millions)
	Net income	$	19.5		$	16.2		$	45.7		$	53
	Other comprehensive income (loss):
	Change in currency translation adjustment		5.6			5.3			(0.4	)		1.9
	Change in foreign currency transactions of long-term subsidiary investments		0.3			2.5			(6.6	)		2.2
	Change in unrecognized pension transition asset, net of tax benefit of $0.0, $0.1, $0.0 and $0.1		0			(0.1	)		0			(0.2	)
	Change in unrecognized prior service cost, net of tax expense of $0.0, $0.0, $0.0 and $0.0		0			0.1			0.1			0.1
	Change in unrecognized pension net loss, net of tax expense of $0.8, $0.8, $2.3 and $2.3		1.2			1.3			3.5			3.8
	Total comprehensive income		26.6			25.3			42.3			60.8
	Less: comprehensive income attributable to noncontrolling interests		0.8			0.3			1.5			1
	Comprehensive income attributable to Koppers	$	25.8		$	25		$	40.8		$	59.8
	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 12 – Pensions and Postretirement Benefit Plans.
	The following tables present the change in equity for the nine months ended September 30, 2013 and 2012, respectively:
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity
	Balance at December 31, 2012	$	150.6		$	17.5		$	168.1
	Net income		44.5			1.2			45.7
	Issuance of common stock		0.2			0			0.2
	Employee stock plans		5.2			0			5.2
	Other comprehensive income (loss)		(3.7	)		0.3			(3.4	)
	Dividends		(15.9	)		0			(15.9	)
	Investment in noncontrolling interests		0			2.3			2.3
	Repurchases of common stock		(17.5	)		0			(17.5	)
	Balance at September 30, 2013	$	163.4		$	21.3		$	184.7
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity
	Balance at December 31, 2011	$	94.8		$	12.4		$	107.2
	Net income		52			1			53
	Issuance of common stock		0.8			0			0.8
	Employee stock plans		5.4			0			5.4
	Other comprehensive income		7.8			0			7.8
	Dividends		(15.2	)		0			(15.2	)
	Repurchases of common stock		(8.2	)		0			(8.2	)
	Balance at September 30, 2012		$137.40			$13.40			$150.80

Earnings_Per_Common_Share

Earnings Per Common Share	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Earnings Per Common Share	'
	6. 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 September 30,					Nine Months Ended September 30,
		2013			2012		2013			2012
	(Dollars in millions, except share amounts, in thousands, and per share amounts)
	Net income attributable to Koppers	$	19.1		$	16	$	44.5		$	52
	Less: loss from discontinued operations		(0.1	)		0		(0.1	)		(0.1	)
	Income from continuing operations attributable to Koppers	$	19.2		$	16	$	44.6		$	52.1
	Weighted average common shares outstanding:
	Basic		20,577			20,694		20,657			20,709
	Effect of dilutive securities		224			206		230			231
	Diluted		20,801			20,900		20,887			20,940
	Earnings per common share – continuing operations:
	Basic earnings per common share	$	0.93		$	0.77	$	2.16		$	2.52
	Diluted earnings per common share		0.92			0.77		2.13			2.5
	Other data:
	Antidilutive securities excluded from computation of diluted earnings per common share		254			203		236			191

StockBased_Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Stock-Based Compensation	'
	7. 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 (collectively, the “stock units”) to certain employee participants each year starting in 2007. The restricted stock units vest on the third anniversary of the grant date, 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 September 30, 2013:
	Performance Period	Minimum			Target			Maximum
		Shares			Shares			Shares
	2012 – 2014		0			98,453			147,680
	2013 – 2015		0			95,858			143,787
	The following table shows a summary of the status and activity of non-vested stock awards for the nine months ended September 30, 2013:
		Restricted			Performance			Total			Weighted Average
		Stock Units			Stock Units			Stock Units			Grant Date Fair
											Value per Unit
	Non-vested at December 31, 2012		136,098			268,677			404,775		$	36.11
	Granted		62,276			97,318			159,594		$	42.64
	Credited from dividends		3,526			7,064			10,590		$	35.17
	Performance stock unit adjustment		0			43,921			43,921		$	40.09
	Vested		(46,314	)		(85,798	)		(132,112	)	$	29.81
	Forfeited		(2,059	)		(3,084	)		(5,143	)	$	40.34
	Non-vested at September 30, 2013		153,527			328,098			481,625		$	40.29
	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 2013 Grant			February 2012 Grant			February 2011 Grant
	Grant date price per share of option award	$	42.76		$	38.21		$	40.26
	Expected dividend yield per share		2.75	%		2.75	%		2.5	%
	Expected life in years		6.5			6.5			6.5
	Expected volatility		53.77	%		55.06	%		60	%
	Risk-free interest rate		1.29	%		1.34	%		3.02	%
	Grant date fair value per share of option awards	$	17.28		$	15.82		$	19.28
	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 nine months ended September 30, 2013:
		Options			Weighted Average			Weighted Average			Aggregate Intrinsic
					Exercise Price			Remaining			Value (in millions)
					per Option			Contractual Term
								(in years)
	Outstanding at December 31, 2012		331,799		$	34.07
	Granted		94,532		$	42.76
	Exercised		(5,251	)	$	39.04
	Outstanding at September 30, 2013		421,080		$	35.96			7.11		$	2.8
	Exercisable at September 30, 2013		167,565		$	29.15			4.94		$	2.3
	Total stock-based compensation expense recognized for the three and nine months ended September 30, 2013 and 2012 is as follows:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
	(Dollars in millions)
	Stock-based compensation expense recognized:
	Selling, general and administrative expenses	$	1.9		$	1.9		$	4.7		$	5.1
	Less related income tax benefit		0.8			0.8			1.9			2
		$	1.1		$	1.1		$	2.8		$	3.1
	As of September 30, 2013, total future compensation expense related to non-vested stock-based compensation arrangements totaled $8.0 million and the weighted-average period over which this cost is expected to be recognized is approximately 21 months.

Segment_Information

Segment Information	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Segment Information	'
	8. Segment Information
	The Company has two reportable segments: Carbon Materials and Chemicals and Railroad and Utility Products and Services. The Company’s reportable segments are 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 September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
	(Dollars in millions)
	Revenues from external customers:
	Carbon Materials & Chemicals	$	241.6		$	241.1		$	692.4		$	757.3
	Railroad & Utility Products		153.6			146.8			444.1			422.8
	Total	$	395.2		$	387.9		$	1,136.50		$	1,180.10
	Intersegment revenues:
	Carbon Materials & Chemicals	$	23.3		$	27		$	70.9		$	83.8
	Depreciation and amortization expense:
	Carbon Materials & Chemicals	$	4.5		$	4.2		$	13.5		$	12.8
	Railroad & Utility Products		2.7			2.5			8.3			8.3
	Total	$	7.2		$	6.7		$	21.8		$	21.1
	Operating profit:
	Carbon Materials & Chemicals	$	21.8		$	18.4		$	47.4		$	65.1
	Railroad & Utility Products		17.8			12.8			46.6			36.9
	Corporate		(0.5	)		(0.4	)		(1.5	)		(1.3	)
	Total	$	39.1		$	30.8		$	92.5		$	100.7
	The following table sets forth certain tangible and intangible assets allocated to each of the Company’s segments as of the dates indicated:
		September 30,			December 31,
		2013			2012
	(Dollars in millions)
	Segment assets:
	Carbon Materials and Chemicals	$	531.2		$	516.3
	Railroad and Utility Products and Services		181.5			205
	All other		48.4			58.7
	Total	$	761.1		$	780
	Goodwill:
	Carbon Materials and Chemicals	$	68.5		$	70.2
	Railroad and Utility Products and Services		4.9			5.4
	Total	$	73.4		$	75.6

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	9. Income Taxes
	Effective Tax Rate
	Income taxes as a percentage of pretax income before discrete items was 46.4 percent and 35.2 percent for the three months ended September 30, 2013 and 2012, respectively. Discrete items included in income taxes for the three months ended September 30, 2013 consisted of a net tax benefit of $1.6 million primarily due to tax benefits on amended tax returns for prior years and changes in unrecognized tax benefits offset by the effect of a United Kingdom corporate tax rate reduction. Discrete items included in income taxes for the three months ended September 30, 2012 consisted of a net tax benefit of $0.3 million due primarily to changes in unrecognized tax benefits partially offset by the effect of a United Kingdom corporate tax rate change and tax return to provision adjustments.
	The effective tax rate for the third quarter of 2013 differs from the U.S. federal statutory rate of 35.0 percent due to the taxes on foreign earnings (+10.2 percent), state taxes (+1.8 percent), uncertain tax positions (+0.9 percent) and nondeductible expenses (+0.5 percent) partially offset by the domestic manufacturing deduction (-1.8 percent) and tax credits (-0.2 percent). With respect to the third quarter of 2012, the effective tax rate differs from the U.S. federal statutory rate of 35.0 percent due to state taxes (+1.6 percent), nondeductible expenses (+0.4 percent) and unrecognized tax benefits (+0.7 percent) partially offset by the domestic manufacturing deduction (-2.5 percent).
	Income taxes as a percentage of pretax income before discrete items was 43.0 percent and 34.7 percent for the nine months ended September 30, 2013 and 2012, respectively. Discrete items included in income taxes for the nine months ended September 30, 2013 consisted of a net tax benefit of $3.0 million primarily due to tax benefits on amended tax returns for prior years, changes in unrecognized tax benefits, and the fact that the Company is no longer subject to potential income tax examinations for certain years. Discrete items included in income taxes for the nine months ended September 30, 2012 consisted of net tax expense of $0.2 million due primarily to a tax reserve associated with our 2011 European restructuring project partially offset by amended tax returns and deferred tax adjustments.
	The effective tax rate for the first nine months of 2013 differs from the U.S. federal statutory rate of 35.0 percent primarily due to the taxes on foreign earnings (+6.6 percent), state taxes (+1.8 percent), uncertain tax positions (+0.8 percent) and nondeductible expenses (+0.5 percent) partially offset by the domestic manufacturing deduction (-1.7 percent). With respect to the first nine months of 2012, the effective tax rate differs from the U.S. federal statutory rate of 35.0 percent primarily due to state taxes (+1.6 percent), nondeductible expenses (+0.7 percent) and unrecognized tax benefits (+0.8 percent) partially offset by taxes on foreign earnings (-1.5 percent) and the domestic manufacturing deduction (-1.9 percent).
	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. 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 such as the non-conventional fuel tax credit. To the extent that actual results vary from the estimates at the end of the third quarter, the actual tax provision recognized for 2013 could be materially different from the forecasted annual tax provision as of the end of the third 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 2009.
	As of September 30, 2013 and December 31, 2012, the total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate, was approximately $4.4 million and $5.5 million, respectively. Unrecognized tax benefits totaled $6.8 million and $7.7 million as of September 30, 2013 and December 31, 2012, respectively. The Company recognizes interest expense and any related penalties from uncertain tax positions in income tax expense. As of September 30, 2013 and December 31, 2012 the Company had accrued approximately $1.1 million and $1.3 million for interest and penalties.

Inventories

Inventories	9 Months Ended
	Sep. 30, 2013
Inventory Disclosure [Abstract]	'
Inventories	'
	10. Inventories
	Net inventories as of September 30, 2013 and December 31, 2012 are summarized in the table below:
		September 30,		December 31,
		2013		2012
	(Dollars in millions)
	Raw materials	$	103	$	118.2
	Work in process		18.3		20
	Finished goods		100.1		109.7
			221.4		247.9
	Less revaluation to LIFO		55		52.1
	Net	$	166.4	$	195.8

Property_Plant_and_Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2013
Property Plant And Equipment [Abstract]	'
Property, Plant and Equipment	'
	11. Property, Plant and Equipment
	Property, plant and equipment as of September 30, 2013 and December 31, 2012 are summarized in the table below:
		September 30,		December 31,
		2013		2012
	(Dollars in millions)
	Land	$	9.2	$	7
	Buildings		35.7		36.4
	Machinery and equipment		639.3		616.6
			684.2		660
	Less accumulated depreciation		514.8		498.9
	Net	$	169.4	$	161.1
	In February 2012, approximately 400 tons of carbon pitch leaked from a storage tank at the Company’s terminal facility in Portland, Victoria, Australia. All of the coal tar pitch was contained within the tank farm area and was recovered.
	Insurance recoveries associated with the leak were a net $0.2 million and $1.2 million for the three and nine months ended September 30, 2013, respectively. Costs directly associated with the leak were $1.3 million and $3.7 million for the three and nine months ended September 30, 2012, respectively, and include inventory losses, emergency response expenses, incremental logistics costs, and material clean-up and removal expenses, net of insurance recoveries.
	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 by March 15, 2014 in an effort to improve the air quality in the Tangshan area. The Company’s 60-percent owned subsidiary, Koppers (China) Carbon & Chemical Company Limited (“KCCC”) is located within TISCO’s property and relies on its operations for a significant portion of raw material supply, utilities and other shared services. At the same time, the Tangshan Government has requested that KCCC consider the relocation of its operations and offered assistance to KCCC in this regard, although no specific details have been provided to the Company on the extent and nature of such assistance. Closure of the TISCO coke batteries could impact KCCC’s ability to operate its coal tar distillation plant on a long-term basis. The Company has entered discussions with its non-controlling partner in KCCC, TISCO, and the Tangshan Government to evaluate its options, which include remaining at the current location and continuing to operate or remaining at its current location on a temporary basis and transitioning to a new location.
	The closure or relocation 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, 2012, KCCC contributed operating profit of approximately $3.5 million after deducting profit attributable to non-controlling interests. As of September 30, 2013, the net book value of fixed assets was approximately $15 million. The Company believes it would be able to continue fulfilling current domestic Chinese customers with capacity at Koppers (Jiangsu) Carbon Chemical Company Limited, which is scheduled for production start-up in mid-2014. The Company further believes it would be able to continue to supply all its export commitments through its other 30-percent owned Chinese company and other commercial relationships in China. However, the Company’s margin on export sales would be negatively affected due to its lower ownership interest in these companies.

Pensions_and_Postretirement_Be

Pensions and Postretirement Benefit Plans	9 Months Ended
	Sep. 30, 2013
Compensation And Retirement Disclosure [Abstract]	'
Pensions and Postretirement Benefit Plans	'
	12. 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 and nine months ended September 30, 2013 and 2012:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
	(Dollars in millions)
	Service cost	$	0.9		$	0.8		$	2.6		$	2.6
	Interest cost		2.7			2.8			8			8
	Expected return on plan assets		(3.2	)		(2.7	)		(9.5	)		(8.0	)
	Amortization of prior service cost		0			0			0.1			0.1
	Amortization of net loss		1.9			2			5.7			6.1
	Amortization of transition asset		0			(0.0	)		0			(0.2	)
	Net periodic benefit cost	$	2.3		$	2.9		$	6.9		$	8.6
	Defined contribution plan expense	$	1.2		$	1.1		$	4.1		$	3.8
	Multi-employer pension plan expense		0.1			0.1			0.3			0.3
	Other postretirement benefit plans		0.1			0.2			0.4			0.5

Debt

Debt	9 Months Ended
	Sep. 30, 2013
Debt Disclosure [Abstract]	'
Debt	'
	13. Debt
	Debt at September 30, 2013 and December 31, 2012 was as follows:
		Weighted			Maturity		September 30,		December 31,
		Average					2013		2012
		Interest Rate
	(Dollars in millions)
	Revolving Credit Facility		0	%		2018	$	0	$	0
	Senior Notes		7 7/8	%		2019		296.4		296.1
	Total debt							296.4		296.1
	Less short term debt and current maturities of long-term debt							0		0
	Long-term debt						$	296.4	$	296.1
	Revolving Credit Facility
	The Koppers Inc. revolving credit facility agreement provides for a revolving credit facility of up to $300.0 million at variable rates. In March 2013, the Company extended the revolving credit agreement term to March 27, 2018. 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 and $0.2 million for the three months ended September 30, 2013 and 2012 and $0.8 million and $0.7 million for the nine months ended September 30, 2013 and 2012, respectively. Commitment fees are charged to interest expense.
	As of September 30, 2013, the Company had $286.9 million of unused revolving credit availability for working capital purposes after restrictions from certain letter of credit commitments and other covenants. As of September 30, 2013, $9.1 million of commitments were utilized by outstanding letters of credit.
	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	9 Months Ended
	Sep. 30, 2013
Asset Retirement Obligation Disclosure [Abstract]	'
Asset Retirement Obligations	'
	14. 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:
		September 30,			December 31,
		2013			2012
	(Dollars in millions)
	Balance at beginning of year	$	21.5		$	21.3
	Accretion expense		0.8			1.1
	Revision in estimated cash flows, net		0			1.8
	Cash expenditures		(4.1	)		(3.0	)
	Currency translation		(0.5	)		0.3
	Balance at end of period	$	17.7		$	21.5

Deferred_Revenue_from_Extended

Deferred Revenue from Extended Product Warranty Liabilities	9 Months Ended
	Sep. 30, 2013
Revenue Recognition [Abstract]	'
Deferred Revenue from Extended Product Warranty Liabilities	'
	15. 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:
		September 30,			December 31,
		2013			2012
	(Dollars in millions)
	Balance at beginning of year	$	3.9		$	4.8
	Revenue earned		(0.5	)		(0.9	)
	Balance at end of period	$	3.4		$	3.9

Commitments_and_Contingent_Lia

Commitments and Contingent Liabilities	9 Months Ended
	Sep. 30, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Commitments and Contingent Liabilities	'
	16. 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 110 plaintiffs in 60 cases pending as of September 30, 2013 as compared to 136 plaintiffs in 75 cases pending as of December 31, 2012. As of September 30, 2013, there are a total of 56 cases pending in state court in Pennsylvania, three in Arkansas, and one case pending in state court in Tennessee.
	The plaintiffs in all 60 pending cases seek to recover compensatory damages, while plaintiffs in 55 cases also seek to recover punitive damages. The plaintiffs in the 56 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. On May 31, 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. Koppers Holdings Inc. filed a motion to dismiss alleging that the Court lacks personal jurisdiction over it, and on September 9, 2013, the district court granted the motion and dismissed Koppers Holdings as a defendant. On October 8, 2013, the plaintiffs filed a notice of appeal with the district court with respect to the dismissal order. Koppers Holdings Inc. has filed a motion to dismiss plaintiffs’ appeal.
	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 a claim for lost profits of approximately $1.7 million. On July 11, 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. The arbitration hearing has tentatively been scheduled for January 2014. Koppers Netherlands has not received detailed information used by the unaffiliated plant to determine this alleged loss, and, as a result, Koppers Netherlands is unable to determine the validity of the actual loss incurred. 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, 2012, amounts paid by Beazer East as a result of its environmental remediation obligations under the Indemnity have averaged in total approximately $16 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 operates 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.
	On March 30, 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 $0.6 million at September 30, 2013, 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 $4.3 million and has recorded a receivable, net of cash collections, from the owner of the adjacent property of $2.8 million as of September 30, 2013.
	In December 2011, the Company ceased manufacturing operations at its Continental Carbon 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 has accrued its expected cost of site remediation resulting from the closure of $5.9 million as of September 30, 2013.
	Environmental Reserves Rollforward. The following table reflects changes in the accrued liability for environmental matters, of which $7.9 million and $8.5 million are classified as current liabilities at September 30, 2013 and 2012, respectively:
		Period ended
		September 30,			December 31,
		2013			2012
	(Dollars in millions)
	Balance at beginning of year	$	14.1		$	17.7
	Expense		1			1
	Reversal of reserves		(1.2	)		(0.4	)
	Cash expenditures		(0.8	)		(4.6	)
	Currency translation		(1.3	)		0.4
	Balance at end of year	$	11.8		$	14.1
	The reversal of reserves includes a reversal of $1.1 million due to the sale of a property to an unaffiliated third party in September 2013. The unaffiliated third party assumed the site’s remediation liabilities.

Subsidiary_Guarantor_Informati

Subsidiary Guarantor Information for Koppers Inc. Senior Notes	9 Months Ended
	Sep. 30, 2013
Text Block [Abstract]	'
Subsidiary Guarantor Information for Koppers Inc. Senior Notes	'
	17. 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 World-Wide Ventures Corporation, Koppers Delaware, Inc., Koppers Concrete Products, Inc., Concrete Partners, Inc., and Koppers Asia LLC.
	Separate condensed consolidating financial statement information for Koppers Holdings Inc. (the parent), Koppers Inc., the domestic guarantor subsidiaries and the non-guarantor subsidiaries as of September 30, 2013 and December 31, 2012 and for the three and nine months ended September 30, 2013 and 2012 is as follows. Certain amounts have been reclassified in the Condensed Consolidated Statements of Comprehensive Income for the three and nine months ended September 30, 2012 to reflect affiliated dividends and affiliated interest income.
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	230.1		$	11.9		$	164		$	(10.8	)	$	395.2
	Cost of sales including depreciation and amortization		0			197.5			7.2			144			(10.9	)		337.8
	Selling, general and administrative		0.5			10.8			0.1			6.9			0			18.3
	Operating profit (loss)		(0.5	)		21.8			4.6			13.1			0.1			39.1
	Other income (expense)		19.4			0.4			1.1			0.8			(20.4	)		1.3
	Interest expense (income)		0			6.7			0.2			0.8			(1.0	)		6.7
	Income taxes		(0.2	)		10.2			0			4.1			0			14.1
	Income from continuing operations		19.1			5.3			5.5			9			(19.3	)		19.6
	Discontinued operations		0			0			0			(0.1	)		0			(0.1	)
	Noncontrolling interests		0			0			0			0.4			0			0.4
	Net income attributable to Koppers	$	19.1		$	5.3		$	5.5		$	8.5		$	(19.3	)	$	19.1
	Comprehensive income attributable to Koppers	$	25.8		$	6.4		$	5.7		$	13.8		$	(25.9	)	$	25.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	238.2		$	15.1		$	147.8		$	(13.2	)	$	387.9
	Cost of sales including depreciation and amortization		0			211			9.3			129.7			(11.9	)		338.1
	Selling, general and administrative		0.4			11.6			0.4			6.6			0			19
	Operating profit (loss)		(0.4	)		15.6			5.4			11.5			(1.3	)		30.8
	Other income (expense)		16.3			0.4			0.3			(0.1	)		(16.3	)		0.6
	Interest expense (income)		0.1			6.9			0			1.2			(1.3	)		6.9
	Income taxes		(0.2	)		7			0.1			1.4			0			8.3
	Income from continuing operations		16			2.1			5.6			8.8			(16.3	)		16.2
	Discontinued operations		0			0			0			0			0			0
	Noncontrolling interests		0			0			0			0.2			0			0.2
	Net income attributable to Koppers	$	16		$	2.1		$	5.6		$	8.6		$	(16.3	)	$	16
	Comprehensive income attributable to Koppers	$	25		$	3.3		$	8.1		$	13.9		$	(25.3	)	$	25
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	660.3		$	48.5		$	470		$	(42.3	)	$	1,136.50
	Cost of sales including depreciation and amortization		0			580.6			34.3			419.3			(42.4	)		991.8
	Selling, general and administrative		1.5			29.7			0.7			20.3			0			52.2
	Operating profit (loss)		(1.5	)		50			13.5			30.4			0.1			92.5
	Other income (expense)		45.4			1.3			6.3			1.5			(51.7	)		2.8
	Interest expense (income)		0			20.2			0.1			3.1			(3.2	)		20.2
	Income taxes		(0.6	)		21.3			0.2			8.4			0			29.3
	Income from continuing operations		44.5			9.8			19.5			20.4			(48.4	)		45.8
	Discontinued operations		0			0			0			(0.1	)		0			(0.1	)
	Noncontrolling interests		0			0			0			1.2			0			1.2
	Net income attributable to Koppers	$	44.5		$	9.8		$	19.5		$	19.1		$	(48.4	)	$	44.5
	Comprehensive income attributable to Koppers	$	40.8		$	13		$	12.9		$	18.7		$	(44.6	)	$	40.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
Net sales	$	0		$	689.1		$	73		$	466.7		$	(48.7	)	$	1,180.10
Cost of sales including depreciation and amortization		0			601.9			49.2			412.9			(39.7	)		1,024.30
Selling, general and administrative		1.3			33			1.6			19.2			0			55.1
Operating profit (loss)		(1.3	)		54.2			22.2			34.6			(9.0	)		100.7
Other income (expense)		52.9			0.4			0.8			0.5			(52.9	)		1.7
Interest expense (income)		0.1			20.7			0			3.9			(3.9	)		20.8
Income taxes		(0.5	)		20.5			0.3			8.2			0			28.5
Income from continuing operations		52			13.4			22.7			23			(58.0	)		53.1
Discontinued operations		0			0			0			(0.1	)		0			(0.1	)
Noncontrolling interests		0			0			0			1			0			1
Net income attributable to Koppers	$	52		$	13.4		$	22.7		$	21.9		$	(58.0	)	$	52
Comprehensive income attributable to Koppers	$	59.8		$	16.9		$	24.9		$	24		$	(65.8	)	$	59.8
Condensed Consolidating Balance Sheet
September 30, 2013
	Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Subsidiaries			Adjustments
							Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0		$	8		$	0		$	64.4		$	0		$	72.4
Restricted cash		0			0			1.5			0			0			1.5
Accounts receivable, net		6.7			100.1			339.8			92.9			(357.4	)		182.1
Inventories, net		0			79.5			0			87.1			(0.2	)		166.4
Deferred tax assets		0			16.2			(1.5	)		0			0			14.7
Other current assets		0			6.5			1.8			26.8			0			35.1
Total current assets		6.7			210.3			341.6			271.2			(357.6	)		472.2
Equity investments		161.3			80.8			27.3			4.2			(267.4	)		6.2
Property, plant and equipment, net		0			105.1			0			64.3			0			169.4
Goodwill		0			39.8			0			33.6			0			73.4
Deferred tax assets		0			20.1			(12.4	)		4.9			0			12.6
Other noncurrent assets		0.1			15.6			120.2			51.4			(160.0	)		27.3
Total assets	$	168.1		$	471.7		$	476.7		$	429.6		$	(785.0	)	$	761.1
LIABILITIES AND EQUITY
Accounts payable	$	0.1		$	384.3		$	14.7		$	53.2		$	(357.4	)	$	94.9
Accrued liabilities		4.6			17.1			10.5			39.9			0			72.1
Total current liabilities		4.7			401.4			25.2			93.1			(357.4	)		167
Long-term debt		0			398.5			0			57.9			(160.0	)		296.4
Other long-term liabilities		0			81.1			2.4			29.5			0			113
Total liabilities		4.7			881			27.6			180.5			(517.4	)		576.4
Koppers shareholders’ equity		163.4			(409.3	)		449.1			227.8			(267.6	)		163.4
Noncontrolling interests		0			0			0			21.3			0			21.3
Total liabilities and equity	$	168.1		$	471.7		$	476.7		$	429.6		$	(785.0	)	$	761.1
Condensed Consolidating Balance Sheet
December 31, 2012
	Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Subsidiaries			Adjustments
							Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0		$	4.8		$	0		$	61.9		$	0		$	66.7
Receivables, net		6.9			89.9			324.9			86.8			(345.8	)		162.7
Inventories, net		0			102.2			0			93.9			(0.3	)		195.8
Deferred tax assets		0			16.4			(1.5	)		0.2			0			15.1
Other current assets		0			8			2.8			30.1			0			40.9
Total current assets		6.9			221.3			326.2			272.9			(346.1	)		481.2
Equity investments		148.7			77.1			27.3			3.8			(251.1	)		5.8
Property, plant and equipment, net		0			105.7			0			55.4			0			161.1
Goodwill		0			39.8			0			35.8			0			75.6
Deferred tax assets		0			33.5			(12.4	)		6.1			0			27.2
Other noncurrent assets		0			15.8			126.7			52.5			(165.9	)		29.1
Total assets	$	155.6		$	493.2		$	467.8		$	426.5		$	(763.1	)	$	780
LIABILITIES AND EQUITY
Accounts payable	$	0.1		$	371.7		$	17		$	60.6		$	(345.9	)	$	103.5
Accrued liabilities		4.9			15.9			12.2			44.7			0			77.7
Total current liabilities		5			387.6			29.2			105.3			(345.9	)		181.2
Long-term debt		0			397.6			0			64.4			(165.9	)		296.1
Other long-term liabilities		0			101.2			2.4			31			0			134.6
Total liabilities		5			886.4			31.6			200.7			(511.8	)		611.9
Koppers shareholders’ equity		150.6			(393.2	)		436.2			208.3			(251.3	)		150.6
Noncontrolling interests		0			0			0			17.5			0			17.5
Total liabilities and equity	$	155.6		$	493.2		$	467.8		$	426.5		$	(763.1	)	$	780
Condensed Consolidating Statement of Cash Flows
For the Nine Months Ended September 30, 2013
	Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Subsidiaries			Adjustments
							Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities	$	32.6		$	39.7		$	0		$	16.8		$	(23.5	)	$	65.6
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(13.3	)		0			(16.1	)		0			(29.4	)
Net cash proceeds (payments) from divestitures and asset sales		0			1.4			0			1			0			2.4
Net cash provided by (used in) investing activities		0			(11.9	)		0			(15.1	)		0			(27.0	)
Cash provided by (used in) financing activities:
Deferred financing costs		0			(1.2	)		0			0			0			(1.2	)
Dividends paid		(15.3	)		(23.5	)		0			0			23.5			(15.3	)
Other financing activities		0			0			0			2.3			0			2.3
Stock issued (repurchased)		(17.3	)		0			0			0			0			(17.3	)
Net cash provided by (used in) financing activities		(32.6	)		(24.7	)		0			2.3			23.5			(31.5	)
Effect of exchange rates on cash		0			0.1			0			(1.5	)		0			(1.4	)
Net increase (decrease) in cash and cash equivalents		0			3.2			0			2.5			0			5.7
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		$	8		$	0		$	64.4		$	0		$	72.4
Condensed Consolidating Statement of Cash Flows
For the Nine Months Ended September 30, 2012
	Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Subsidiaries			Adjustments
							Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities	$	21.8		$	32		$	0		$	15.5		$	(14.8	)	$	54.5
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(12.2	)		0			(3.6	)		0			(15.8	)
Net cash proceeds (payments) from divestitures and asset sales		0			0.3			0			0.4			0			0.7
Net cash provided by (used in) investing activities		0			(11.9	)		0			(3.2	)		0			(15.1	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0.1			(5.0	)		0			(0.1	)		0			(5.0	)
Deferred financing costs		0			(0.1	)		0			0			0			(0.1	)
Stock issued (repurchased)		(7.4	)		0			0			0			0			(7.4	)
Dividends paid		(14.5	)		(14.8	)		0			0			14.8			(14.5	)
Net cash provided by (used in) financing activities		(21.8	)		(19.9	)		0			(0.1	)		14.8			(27.0	)
Effect of exchange rates on cash		0			(0.1	)		0			2.5			0			2.4
Net increase (decrease) in cash and cash equivalents		0			0.1			0			14.7			0			14.8
Cash and cash equivalents at beginning of year		0			0			0			54.1			0			54.1
Cash and cash equivalents at end of period	$	0		$	0.1		$	0		$	68.8		$	0		$	68.9

Subsidiary_Guarantor_Informati1

Subsidiary Guarantor Information for Shelf Registration	9 Months Ended
	Sep. 30, 2013
Text Block [Abstract]	'
Subsidiary Guarantor Information for Shelf Registration	'
	18. 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. 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 consolidated financial information for subsidiary guarantors will be revised to identify the subsidiaries that actually provided guarantees.
	Separate condensed consolidating financial statement information for the parent, Koppers Inc., domestic guarantor subsidiaries, foreign guarantor subsidiaries and non-guarantor subsidiaries as of September 30, 2013 and December 31, 2012 and for the three and nine months ended September 30, 2013 and 2012 is as follows. Certain amounts have been reclassified in the Condensed Consolidated Statements of Comprehensive Income for the three and nine months ended September 30, 2012 to reflect affiliated dividends and affiliated interest income.
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	230.1		$	11.9		$	120.7		$	43.4		$	(10.9	)	$	395.2
	Cost of sales including depreciation and amortization		0			197.5			7.2			103.6			40.5			(11.0	)		337.8
	Selling, general and administrative		0.5			10.8			0.1			5.5			1.4			0			18.3
	Operating profit (loss)		(0.5	)		21.8			4.6			11.6			1.5			0.1			39.1
	Other income (expense)		19.4			0.4			1.1			0.7			0.1			(20.4	)		1.3
	Interest expense (income)		0			6.7			0.2			0.6			0.2			(1.0	)		6.7
	Income taxes		(0.2	)		10.2			0			3.8			0.3			0			14.1
	Income from continuing operations		19.1			5.3			5.5			7.9			1.1			(19.3	)		19.6
	Discontinued operations		0			0			0			(0.1	)		0			0			(0.1	)
	Noncontrolling interests		0			0			0			0			0.4			0			0.4
	Net income attributable to Koppers	$	19.1		$	5.3		$	5.5		$	7.8		$	0.7		$	(19.3	)	$	19.1
	Comprehensive income attributable to Koppers	$	25.8		$	6.4		$	5.7		$	13.2		$	1.3		$	(26.6	)	$	25.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2012
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	238.2		$	15.1		$	118.6		$	29.2		$	(13.2	)	$	387.9
	Cost of sales including depreciation and amortization					211			9.3			102.3			27.4			(11.9	)		338.1
	Selling, general and administrative		0.4			11.6			0.4			5.6			1			0			19
	Operating profit (loss)		(0.4	)		15.6			5.4			10.7			0.8			(1.3	)		30.8
	Other income (expense)		16.3			0.4			0.3			0.1			(0.2	)		(16.3	)		0.6
	Interest expense (income)		0.1			6.9			0			1			0.2			(1.3	)		6.9
	Income taxes		(0.2	)		7			0.1			1.4			0			0			8.3
	Income from continuing operations		16			2.1			5.6			8.4			0.4			(16.3	)		16.2
	Discontinued operations		0			0			0			0			0			0			0
	Noncontrolling interests		0			0			0			0			0.2			0			0.2
	Net income attributable to Koppers	$	16		$	2.1		$	5.6		$	8.4		$	0.2		$	(16.3	)	$	16
	Comprehensive income attributable to Koppers	$	25		$	3.3		$	8.1		$	14.3		$	0.4		$	(26.1	)	$	25
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	660.3		$	48.5		$	348.6		$	123.9		$	(44.8	)	$	1,136.50
	Cost of sales including depreciation and amortization		0			580.6			34.3			305.7			116.1			(44.9	)		991.8
	Selling, general and administrative		1.5			29.7			0.7			16.8			3.5			0			52.2
	Operating profit (loss)		(1.5	)		50			13.5			26.1			4.3			0.1			92.5
	Other income (expense)		45.4			1.3			6.3			0.8			0.7			(51.7	)		2.8
	Interest expense (income)		0			20.2			0.1			2.5			0.6			(3.2	)		20.2
	Income taxes		(0.6	)		21.3			0.2			7.4			1			0			29.3
	Income from continuing operations		44.5			9.8			19.5			17			3.4			(48.4	)		45.8
	Discontinued operations		0			0			0			(0.1	)		0			0			(0.1	)
	Noncontrolling interests		0			0			0			0			1.2			0			1.2
	Net income attributable to Koppers	$	44.5		$	9.8		$	19.5		$	16.9		$	2.2		$	(48.4	)	$	44.5
	Comprehensive income attributable to Koppers	$	40.8		$	13		$	12.9		$	14.4		$	2.8		$	(43.1	)	$	40.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2012
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
Net sales	$	0		$	689.1		$	73		$	355.4		$	111.3		$	(48.7	)	$	1,180.10
Cost of sales including depreciation and amortization		0			601.9			49.2			309.6			103.3			(39.7	)		1,024.30
Selling, general and administrative		1.3			33			1.6			16.7			2.5			0			55.1
Operating profit (loss)		(1.3	)		54.2			22.2			29.1			5.5			(9.0	)		100.7
Other income (expense)		52.9			0.4			0.8			0.1			0.4			(52.9	)		1.7
Interest expense (income)		0.1			20.7			0			3			0.9			(3.9	)		20.8
Income taxes		(0.5	)		20.5			0.3			7.5			0.7			0			28.5
Income from continuing operations		52			13.4			22.7			18.7			4.3			(58.0	)		53.1
Discontinued operations		0			0			0			(0.1	)		0			0			(0.1	)
Noncontrolling interests		0			0			0			0			1			0			1
Net income attributable to Koppers	$	52		$	13.4		$	22.7		$	18.6		$	3.3		$	(58.0	)	$	52
Comprehensive income attributable to Koppers	$	59.8		$	16.9		$	24.9		$	21.4		$	3.3		$	(66.5	)	$	59.8
Condensed Consolidating Balance Sheet
September 30, 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		$	8		$	0		$	48.3		$	16.1		$	0		$	72.4
Restricted cash		0			0			1.5			0			0			0			1.5
Accounts receivable, net		6.7			100.1			339.8			58.7			34.2			(357.4	)		182.1
Inventories, net		0			79.5			0			79.9			7.2			(0.2	)		166.4
Deferred tax assets		0			16.2			(1.5	)		0			0			0			14.7
Other current assets		0			6.5			1.8			10.6			16.2			0			35.1
Total current assets		6.7			210.3			341.6			197.5			73.7			(357.6	)		472.2
Equity investments		161.3			80.8			27.3			36.4			4.2			(303.8	)		6.2
Property, plant and equipment, net		0			105.1			0			41			23.3			0			169.4
Goodwill		0			39.8			0			32.3			1.3			0			73.4
Deferred tax assets		0			20.1			(12.4	)		6.5			(1.6	)		0			12.6
Other noncurrent assets		0.1			15.6			120.2			10.4			41.1			(160.1	)		27.3
Total assets	$	168.1		$	471.7		$	476.7		$	324.1		$	142		$	(821.5	)	$	761.1
LIABILITIES AND EQUITY
Accounts payable	$	0.1		$	384.3		$	14.7		$	32.9		$	20.3		$	(357.4	)	$	94.9
Accrued liabilities		4.6			17.1			10.5			30.3			9.6			0			72.1
Total current liabilities		4.7			401.4			25.2			63.2			29.9			(357.4	)		167
Long-term debt		0			398.5			0			57.9			0			(160.0	)		296.4
Other long-term liabilities		0			81.1			2.4			22.7			6.8			0			113
Total liabilities		4.7			881			27.6			143.8			36.7			(517.4	)		576.4
Koppers shareholders’ equity		163.4			(409.3	)		449.1			180.3			84			(304.1	)		163.4
Noncontrolling interests		0			0			0			0			21.3			0			21.3
Total liabilities and equity	$	168.1		$	471.7		$	476.7		$	324.1		$	142		$	(821.5	)	$	761.1
Condensed Consolidating Balance Sheet
December 31, 2012
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0		$	4.8		$	0		$	40.7		$	21.2		$	0		$	66.7
Receivables, net		6.9			89.9			324.9			65.9			21.2			(346.1	)		162.7
Inventories, net		0			102.2			0			86.7			7.2			(0.3	)		195.8
Deferred tax assets		0			16.4			(1.5	)		0			0.2			0			15.1
Other current assets		0			8			2.8			17.6			12.5			0			40.9
Total current assets		6.9			221.3			326.2			210.9			62.3			(346.4	)		481.2
Equity investments		148.7			77.1			27.3			30.2			3.8			(281.3	)		5.8
Property, plant and equipment, net		0			105.7			0			40.7			14.7			0			161.1
Goodwill		0			39.8			0			34.4			1.4			0			75.6
Deferred tax assets		0			33.5			(12.4	)		7.6			(1.5	)		0			27.2
Other noncurrent assets		0			15.8			126.7			12.1			40.3			(165.8	)		29.1
Total assets	$	155.6		$	493.2		$	467.8		$	335.9		$	121		$	(793.5	)	$	780
LIABILITIES AND EQUITY
Accounts payable	$	0.1		$	371.7		$	17		$	42.2		$	18.6		$	(346.1	)	$	103.5
Accrued liabilities		4.9			15.9			12.2			35.7			9			0			77.7
Total current liabilities		5			387.6			29.2			77.9			27.6			(346.1	)		181.2
Long-term debt		0			397.6			0			64.4			0			(165.9	)		296.1
Other long-term liabilities		0			101.2			2.4			24.5			6.5			0			134.6
Total liabilities		5			886.4			31.6			166.8			34.1			(512.0	)		611.9
Koppers shareholders’ equity		150.6			(393.2	)		436.2			169.1			69.4			(281.5	)		150.6
Noncontrolling interests		0			0			0			0			17.5			0			17.5
Total liabilities and equity	$	155.6		$	493.2		$	467.8		$	335.9		$	121		$	(793.5	)	$	780
Condensed Consolidating Statement of Cash Flows
For the Nine Months Ended September 30, 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	$	32.6		$	39.7		$	0		$	14.9		$	1.9		$	(23.5	)	$	65.6
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(13.3	)		0			(6.6	)		(9.5	)		0			(29.4	)
Net cash proceeds (payments) from divestitures and asset sales		0			1.4			0			1.1			(0.1	)		0			2.4
Net cash provided by (used in) investing activities		0			(11.9	)		0			(5.5	)		(9.6	)		0			(27.0	)
Cash provided by (used in) financing activities:
Deferred financing costs		0			(1.2	)		0			0			0			0			(1.2	)
Dividends paid		(15.3	)		(23.5	)		0			0			0			23.5			(15.3	)
Other financing activities		0			0			0			0			2.3			0			2.3
Stock issued (repurchased)		(17.3	)		0			0			0			0			0			(17.3	)
Net cash provided by (used in) financing activities		(32.6	)		(24.7	)		0			0			2.3			23.5			(31.5	)
Effect of exchange rates on cash		0			0.1			0			(1.8	)		0.3			0			(1.4	)
Net increase (decrease) in cash and cash equivalents		0			3.2			0			7.6			(5.1	)		0			5.7
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		$	8		$	0		$	48.3		$	16.1		$	0		$	72.4
Condensed Consolidating Statement of Cash Flows
For the Nine Months Ended September 30, 2012
	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	$	21.8		$	32		$	0		$	21.5		$	(6.0	)	$	(14.8	)	$	54.5
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(12.2	)		0			(3.2	)		(0.4	)		0			(15.8	)
Net cash proceeds (payments) from divestitures and asset sales		0			0.3			0			0.3			0.1			0			0.7
Net cash provided by (used in) investing activities		0			(11.9	)		0			(2.9	)		(0.3	)		0			(15.1	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0.1			(5.0	)		0			0			(0.1	)		0			(5.0	)
Deferred financing costs		0			(0.1	)		0			0			0			0			(0.1	)
Stock issued (repurchased)		(7.4	)		0			0			0			0			0			(7.4	)
Dividends paid		(14.5	)		(14.8	)		0			0			0			14.8			(14.5	)
Net cash provided by (used in) financing activities		(21.8	)		(19.9	)		0			0			(0.1	)		14.8			(27.0	)
Effect of exchange rates on cash		0			(0.1	)		0			2.5			0			0			2.4
Net increase (decrease) in cash and cash equivalents		0			0.1			0			21.1			(6.4	)		0			14.8
Cash and cash equivalents at beginning of year		0			0			0			45.1			9			0			54.1
Cash and cash equivalents at end of period	$	0		$	0.1		$	0		$	66.2		$	2.6		$	0		$	68.9

Related_Party_Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2013
Related Party Transactions [Abstract]	'
Related Party Transactions	'
	19. Related Party Transactions
	In November 2011, the Company loaned $11.7 million to TKK, a 30-percent owned company in China. During 2012, TKK made repayments totaling $2.2 million; accordingly the amount of the loan is $9.5 million as of September 30, 2013. The loan is repayable in November 2013 and is expected to be extended for an additional one-year term.

Basis_of_Presentation_and_New_1

Basis of Presentation and New Accounting Standards (Policies)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Reporting of Amounts Reclassified Out of Other Comprehensive Income	'
	The Financial Accounting Standards Board issued Accounting Standards Update No. 2013-02, Reporting of Amounts Reclassified Out of Other Comprehensive Income (ASU 2013-2). The amendments in ASU 2013-02 require entities to provide additional disclosures regarding amounts that have been reclassified out of other comprehensive income during the periods presented either on the face of the financial statements or in the notes to the financial statements. ASU 2013-02 is effective for interim and annual periods beginning after December 15, 2012. We have elected to present such information in the notes to the financial statements (see Note 5).

Discontinued_Operations_Tables

Discontinued Operations (Tables)	9 Months Ended
	Sep. 30, 2013
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			Inventory			Site			Other			Total
		employee benefits			remediation			writedowns			demolition
	(Dollars in millions)
	Reserve at December 31, 2011	$	1.8		$	6.7		$	0		$	6.2		$	1.2		$	15.9
	Charges		0.1			0			0.4			0			0			0.5
	Costs charged against assets		0			0			(0.4	)		0			0			(0.4	)
	Reversal of accrued charges		0			0			0			0			(0.6	)		(0.6	)
	Cash expenditures		(1.7	)		(0.1	)		0			(0.4	)		(0.5	)		(2.7	)
	Currency translation		0			0.1			0			0.1			0			0.2
	Reserve at December 31, 2012	$	0.2		$	6.7		$	0		$	5.9		$	0.1		$	12.9
	Reversal of accrued charges		(0.1	)		0			0			(0.3	)		0			(0.4	)
	Cash expenditures		0			(0.1	)		0			(1.5	)		0			(1.6	)
	Currency translation		0			(0.7	)		0			(0.5	)		0			(1.2	)
	Reserve at September 30, 2013	$	0.1		$	5.9		$	0		$	3.6		$	0.1		$	9.7
Summary of Net Sales and Operating Profit from Discontinued Operations	'
	Net sales and operating profit from discontinued operations for the three months and nine months ended September 30, 2013 and 2012 consist of the following amounts:
		Three Months						Nine Months
		Ended September 30,						Ended September 30,
		2013			2012			2013			2012
	Net sales	$	0		$	0.3		$	0		$	5.7
	Operating loss		(0.1	)		(0.1	)		(0.2	)		(0.3	)

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2013
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 September 30, 2013 and December 31, 2012 are as follows:
			September 30, 2013				December 31, 2012
			Fair Value		Carrying		Fair Value		Carrying
					Value				Value
	(Dollars in millions)
	Financial assets:
	Cash and cash equivalents, including restricted cash		$	73.9	$	73.9	$	66.7	$	66.7
	Investments and other assets(a)			1.4		1.4		1.4		1.4
	Financial liabilities:
	Long-term debt		$	325.3	$	296.4	$	331.1	$	296.1
	(a)	Excludes equity method investments.

Comprehensive_Income_and_Equit1

Comprehensive Income and Equity (Tables)	9 Months Ended
	Sep. 30, 2013
Equity [Abstract]	'
Schedule of Comprehensive Income	'
	Total comprehensive income for the three and nine months ended September 30, 2013 and 2012 is summarized in the table below:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
	(Dollars in millions)
	Net income	$	19.5		$	16.2		$	45.7		$	53
	Other comprehensive income (loss):
	Change in currency translation adjustment		5.6			5.3			(0.4	)		1.9
	Change in foreign currency transactions of long-term subsidiary investments		0.3			2.5			(6.6	)		2.2
	Change in unrecognized pension transition asset, net of tax benefit of $0.0, $0.1, $0.0 and $0.1		0			(0.1	)		0			(0.2	)
	Change in unrecognized prior service cost, net of tax expense of $0.0, $0.0, $0.0 and $0.0		0			0.1			0.1			0.1
	Change in unrecognized pension net loss, net of tax expense of $0.8, $0.8, $2.3 and $2.3		1.2			1.3			3.5			3.8
	Total comprehensive income		26.6			25.3			42.3			60.8
	Less: comprehensive income attributable to noncontrolling interests		0.8			0.3			1.5			1
	Comprehensive income attributable to Koppers	$	25.8		$	25		$	40.8		$	59.8
Schedule of Change in Equity	'
	The following tables present the change in equity for the nine months ended September 30, 2013 and 2012, respectively:
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity
	Balance at December 31, 2012	$	150.6		$	17.5		$	168.1
	Net income		44.5			1.2			45.7
	Issuance of common stock		0.2			0			0.2
	Employee stock plans		5.2			0			5.2
	Other comprehensive income (loss)		(3.7	)		0.3			(3.4	)
	Dividends		(15.9	)		0			(15.9	)
	Investment in noncontrolling interests		0			2.3			2.3
	Repurchases of common stock		(17.5	)		0			(17.5	)
	Balance at September 30, 2013	$	163.4		$	21.3		$	184.7
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity
	Balance at December 31, 2011	$	94.8		$	12.4		$	107.2
	Net income		52			1			53
	Issuance of common stock		0.8			0			0.8
	Employee stock plans		5.4			0			5.4
	Other comprehensive income		7.8			0			7.8
	Dividends		(15.2	)		0			(15.2	)
	Repurchases of common stock		(8.2	)		0			(8.2	)
	Balance at September 30, 2012		$137.40			$13.40			$150.80

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2013
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					Nine Months
		Ended September 30,					Ended September 30,
		2013			2012		2013			2012
	(Dollars in millions, except share amounts, in thousands, and per share amounts)
	Net income attributable to Koppers	$	19.1		$	16	$	44.5		$	52
	Less: loss from discontinued operations		(0.1	)		0		(0.1	)		(0.1	)
	Income from continuing operations attributable to Koppers	$	19.2		$	16	$	44.6		$	52.1
	Weighted average common shares outstanding:
	Basic		20,577			20,694		20,657			20,709
	Effect of dilutive securities		224			206		230			231
	Diluted		20,801			20,900		20,887			20,940
	Earnings per common share – continuing operations:
	Basic earnings per common share	$	0.93		$	0.77	$	2.16		$	2.52
	Diluted earnings per common share		0.92			0.77		2.13			2.5
	Other data:
	Antidilutive securities excluded from computation of diluted earnings per common share		254			203		236			191

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2013
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 September 30, 2013:
	Performance Period	Minimum			Target			Maximum
		Shares			Shares			Shares
	2012 – 2014		0			98,453			147,680
	2013 – 2015		0			95,858			143,787
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 nine months ended September 30, 2013:
		Restricted			Performance			Total			Weighted Average
		Stock Units			Stock Units			Stock Units			Grant Date Fair
											Value per Unit
	Non-vested at December 31, 2012		136,098			268,677			404,775		$	36.11
	Granted		62,276			97,318			159,594		$	42.64
	Credited from dividends		3,526			7,064			10,590		$	35.17
	Performance stock unit adjustment		0			43,921			43,921		$	40.09
	Vested		(46,314	)		(85,798	)		(132,112	)	$	29.81
	Forfeited		(2,059	)		(3,084	)		(5,143	)	$	40.34
	Non-vested at September 30, 2013		153,527			328,098			481,625		$	40.29
Stock Options Fair Value Assumptions	'
	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 2013 Grant			February 2012 Grant			February 2011 Grant
	Grant date price per share of option award	$	42.76		$	38.21		$	40.26
	Expected dividend yield per share		2.75	%		2.75	%		2.5	%
	Expected life in years		6.5			6.5			6.5
	Expected volatility		53.77	%		55.06	%		60	%
	Risk-free interest rate		1.29	%		1.34	%		3.02	%
	Grant date fair value per share of option awards	$	17.28		$	15.82		$	19.28
Summary of Status and Activity of Stock Options	'
	The following table shows a summary of the status and activity of stock options for the nine months ended September 30, 2013:
		Options			Weighted Average			Weighted Average			Aggregate Intrinsic
					Exercise Price			Remaining			Value (in millions)
					per Option			Contractual Term
								(in years)
	Outstanding at December 31, 2012		331,799		$	34.07
	Granted		94,532		$	42.76
	Exercised		(5,251	)	$	39.04
	Outstanding at September 30, 2013		421,080		$	35.96			7.11		$	2.8
	Exercisable at September 30, 2013		167,565		$	29.15			4.94		$	2.3
Schedule of Stock-Based Compensation Expense Recognized	'
	Total stock-based compensation expense recognized for the three and nine months ended September 30, 2013 and 2012 is as follows:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
	(Dollars in millions)
	Stock-based compensation expense recognized:
	Selling, general and administrative expenses	$	1.9		$	1.9		$	4.7		$	5.1
	Less related income tax benefit		0.8			0.8			1.9			2
		$	1.1		$	1.1		$	2.8		$	3.1

Segment_Information_Tables

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2013
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 September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
	(Dollars in millions)
	Revenues from external customers:
	Carbon Materials & Chemicals	$	241.6		$	241.1		$	692.4		$	757.3
	Railroad & Utility Products		153.6			146.8			444.1			422.8
	Total	$	395.2		$	387.9		$	1,136.50		$	1,180.10
	Intersegment revenues:
	Carbon Materials & Chemicals	$	23.3		$	27		$	70.9		$	83.8
	Depreciation and amortization expense:
	Carbon Materials & Chemicals	$	4.5		$	4.2		$	13.5		$	12.8
	Railroad & Utility Products		2.7			2.5			8.3			8.3
	Total	$	7.2		$	6.7		$	21.8		$	21.1
	Operating profit:
	Carbon Materials & Chemicals	$	21.8		$	18.4		$	47.4		$	65.1
	Railroad & Utility Products		17.8			12.8			46.6			36.9
	Corporate		(0.5	)		(0.4	)		(1.5	)		(1.3	)
	Total	$	39.1		$	30.8		$	92.5		$	100.7
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:
		September 30,			December 31,
		2013			2012
	(Dollars in millions)
	Segment assets:
	Carbon Materials and Chemicals	$	531.2		$	516.3
	Railroad and Utility Products and Services		181.5			205
	All other		48.4			58.7
	Total	$	761.1		$	780
	Goodwill:
	Carbon Materials and Chemicals	$	68.5		$	70.2
	Railroad and Utility Products and Services		4.9			5.4
	Total	$	73.4		$	75.6

Inventories_Tables

Inventories (Tables)	9 Months Ended
	Sep. 30, 2013
Inventory Disclosure [Abstract]	'
Components of Inventories	'
	Net inventories as of September 30, 2013 and December 31, 2012 are summarized in the table below:
		September 30,		December 31,
		2013		2012
	(Dollars in millions)
	Raw materials	$	103	$	118.2
	Work in process		18.3		20
	Finished goods		100.1		109.7
			221.4		247.9
	Less revaluation to LIFO		55		52.1
	Net	$	166.4	$	195.8

Property_Plant_and_Equipment_T

Property, Plant and Equipment (Tables)	9 Months Ended
	Sep. 30, 2013
Property Plant And Equipment [Abstract]	'
Property, Plant and Equipment	'
	Property, plant and equipment as of September 30, 2013 and December 31, 2012 are summarized in the table below:
		September 30,		December 31,
		2013		2012
	(Dollars in millions)
	Land	$	9.2	$	7
	Buildings		35.7		36.4
	Machinery and equipment		639.3		616.6
			684.2		660
	Less accumulated depreciation		514.8		498.9
	Net	$	169.4	$	161.1

Pensions_and_Postretirement_Be1

Pensions and Postretirement Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2013
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 and nine months ended September 30, 2013 and 2012:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2013			2012			2013			2012
	(Dollars in millions)
	Service cost	$	0.9		$	0.8		$	2.6		$	2.6
	Interest cost		2.7			2.8			8			8
	Expected return on plan assets		(3.2	)		(2.7	)		(9.5	)		(8.0	)
	Amortization of prior service cost		0			0			0.1			0.1
	Amortization of net loss		1.9			2			5.7			6.1
	Amortization of transition asset		0			(0.0	)		0			(0.2	)
	Net periodic benefit cost	$	2.3		$	2.9		$	6.9		$	8.6
	Defined contribution plan expense	$	1.2		$	1.1		$	4.1		$	3.8
	Multi-employer pension plan expense		0.1			0.1			0.3			0.3
	Other postretirement benefit plans		0.1			0.2			0.4			0.5

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 30, 2013
Debt Disclosure [Abstract]	'
Schedule of Long-Term Debt Instruments	'
	Debt at September 30, 2013 and December 31, 2012 was as follows:
		Weighted			Maturity		September 30,		December 31,
		Average					2013		2012
		Interest Rate
	(Dollars in millions)
	Revolving Credit Facility		0	%		2018	$	0	$	0
	Senior Notes		7 7/8	%		2019		296.4		296.1
	Total debt							296.4		296.1
	Less short term debt and current maturities of long-term debt							0		0
	Long-term debt						$	296.4	$	296.1

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2013
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:
		September 30,			December 31,
		2013			2012
	(Dollars in millions)
	Balance at beginning of year	$	21.5		$	21.3
	Accretion expense		0.8			1.1
	Revision in estimated cash flows, net		0			1.8
	Cash expenditures		(4.1	)		(3.0	)
	Currency translation		(0.5	)		0.3
	Balance at end of period	$	17.7		$	21.5

Deferred_Revenue_from_Extended1

Deferred Revenue from Extended Product Warranty Liabilities (Tables)	9 Months Ended
	Sep. 30, 2013
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:
		September 30,			December 31,
		2013			2012
	(Dollars in millions)
	Balance at beginning of year	$	3.9		$	4.8
	Revenue earned		(0.5	)		(0.9	)
	Balance at end of period	$	3.4		$	3.9

Commitments_and_Contingent_Lia1

Commitments and Contingent Liabilities (Tables)	9 Months Ended
	Sep. 30, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Changes in Accrued Liability for Environmental Matters	'
	Environmental Reserves Rollforward. The following table reflects changes in the accrued liability for environmental matters, of which $7.9 million and $8.5 million are classified as current liabilities at September 30, 2013 and 2012, respectively:
		Period ended
		September 30,			December 31,
		2013			2012
	(Dollars in millions)
	Balance at beginning of year	$	14.1		$	17.7
	Expense		1			1
	Reversal of reserves		(1.2	)		(0.4	)
	Cash expenditures		(0.8	)		(4.6	)
	Currency translation		(1.3	)		0.4
	Balance at end of year	$	11.8		$	14.1

Subsidiary_Guarantor_Informati2

Subsidiary Guarantor Information for Koppers Inc. Senior Notes (Tables)	9 Months Ended
	Sep. 30, 2013
Text Block [Abstract]	'
Condensed Consolidating Statement of Comprehensive Income	'
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	230.1		$	11.9		$	164		$	(10.8	)	$	395.2
	Cost of sales including depreciation and amortization		0			197.5			7.2			144			(10.9	)		337.8
	Selling, general and administrative		0.5			10.8			0.1			6.9			0			18.3
	Operating profit (loss)		(0.5	)		21.8			4.6			13.1			0.1			39.1
	Other income (expense)		19.4			0.4			1.1			0.8			(20.4	)		1.3
	Interest expense (income)		0			6.7			0.2			0.8			(1.0	)		6.7
	Income taxes		(0.2	)		10.2			0			4.1			0			14.1
	Income from continuing operations		19.1			5.3			5.5			9			(19.3	)		19.6
	Discontinued operations		0			0			0			(0.1	)		0			(0.1	)
	Noncontrolling interests		0			0			0			0.4			0			0.4
	Net income attributable to Koppers	$	19.1		$	5.3		$	5.5		$	8.5		$	(19.3	)	$	19.1
	Comprehensive income attributable to Koppers	$	25.8		$	6.4		$	5.7		$	13.8		$	(25.9	)	$	25.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	238.2		$	15.1		$	147.8		$	(13.2	)	$	387.9
	Cost of sales including depreciation and amortization		0			211			9.3			129.7			(11.9	)		338.1
	Selling, general and administrative		0.4			11.6			0.4			6.6			0			19
	Operating profit (loss)		(0.4	)		15.6			5.4			11.5			(1.3	)		30.8
	Other income (expense)		16.3			0.4			0.3			(0.1	)		(16.3	)		0.6
	Interest expense (income)		0.1			6.9			0			1.2			(1.3	)		6.9
	Income taxes		(0.2	)		7			0.1			1.4			0			8.3
	Income from continuing operations		16			2.1			5.6			8.8			(16.3	)		16.2
	Discontinued operations		0			0			0			0			0			0
	Noncontrolling interests		0			0			0			0.2			0			0.2
	Net income attributable to Koppers	$	16		$	2.1		$	5.6		$	8.6		$	(16.3	)	$	16
	Comprehensive income attributable to Koppers	$	25		$	3.3		$	8.1		$	13.9		$	(25.3	)	$	25
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	660.3		$	48.5		$	470		$	(42.3	)	$	1,136.50
	Cost of sales including depreciation and amortization		0			580.6			34.3			419.3			(42.4	)		991.8
	Selling, general and administrative		1.5			29.7			0.7			20.3			0			52.2
	Operating profit (loss)		(1.5	)		50			13.5			30.4			0.1			92.5
	Other income (expense)		45.4			1.3			6.3			1.5			(51.7	)		2.8
	Interest expense (income)		0			20.2			0.1			3.1			(3.2	)		20.2
	Income taxes		(0.6	)		21.3			0.2			8.4			0			29.3
	Income from continuing operations		44.5			9.8			19.5			20.4			(48.4	)		45.8
	Discontinued operations		0			0			0			(0.1	)		0			(0.1	)
	Noncontrolling interests		0			0			0			1.2			0			1.2
	Net income attributable to Koppers	$	44.5		$	9.8		$	19.5		$	19.1		$	(48.4	)	$	44.5
	Comprehensive income attributable to Koppers	$	40.8		$	13		$	12.9		$	18.7		$	(44.6	)	$	40.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	689.1		$	73		$	466.7		$	(48.7	)	$	1,180.10
	Cost of sales including depreciation and amortization		0			601.9			49.2			412.9			(39.7	)		1,024.30
	Selling, general and administrative		1.3			33			1.6			19.2			0			55.1
Operating profit (loss)		(1.3	)		54.2			22.2			34.6			(9.0	)		100.7
Other income (expense)		52.9			0.4			0.8			0.5			(52.9	)		1.7
Interest expense (income)		0.1			20.7			0			3.9			(3.9	)		20.8
Income taxes		(0.5	)		20.5			0.3			8.2			0			28.5
Income from continuing operations		52			13.4			22.7			23			(58.0	)		53.1
Discontinued operations		0			0			0			(0.1	)		0			(0.1	)
Noncontrolling interests		0			0			0			1			0			1
Net income attributable to Koppers	$	52		$	13.4		$	22.7		$	21.9		$	(58.0	)	$	52
Comprehensive income attributable to Koppers	$	59.8		$	16.9		$	24.9		$	24		$	(65.8	)	$	59.8
Condensed Consolidating Balance Sheet	'
	Condensed Consolidating Balance Sheet
	September 30, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	8		$	0		$	64.4		$	0		$	72.4
	Restricted cash		0			0			1.5			0			0			1.5
	Accounts receivable, net		6.7			100.1			339.8			92.9			(357.4	)		182.1
	Inventories, net		0			79.5			0			87.1			(0.2	)		166.4
	Deferred tax assets		0			16.2			(1.5	)		0			0			14.7
	Other current assets		0			6.5			1.8			26.8			0			35.1
	Total current assets		6.7			210.3			341.6			271.2			(357.6	)		472.2
	Equity investments		161.3			80.8			27.3			4.2			(267.4	)		6.2
	Property, plant and equipment, net		0			105.1			0			64.3			0			169.4
	Goodwill		0			39.8			0			33.6			0			73.4
	Deferred tax assets		0			20.1			(12.4	)		4.9			0			12.6
	Other noncurrent assets		0.1			15.6			120.2			51.4			(160.0	)		27.3
	Total assets	$	168.1		$	471.7		$	476.7		$	429.6		$	(785.0	)	$	761.1
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	384.3		$	14.7		$	53.2		$	(357.4	)	$	94.9
	Accrued liabilities		4.6			17.1			10.5			39.9			0			72.1
	Total current liabilities		4.7			401.4			25.2			93.1			(357.4	)		167
	Long-term debt		0			398.5			0			57.9			(160.0	)		296.4
	Other long-term liabilities		0			81.1			2.4			29.5			0			113
	Total liabilities		4.7			881			27.6			180.5			(517.4	)		576.4
	Koppers shareholders’ equity		163.4			(409.3	)		449.1			227.8			(267.6	)		163.4
	Noncontrolling interests		0			0			0			21.3			0			21.3
	Total liabilities and equity	$	168.1		$	471.7		$	476.7		$	429.6		$	(785.0	)	$	761.1
	Condensed Consolidating Balance Sheet
	December 31, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	4.8		$	0		$	61.9		$	0		$	66.7
	Receivables, net		6.9			89.9			324.9			86.8			(345.8	)		162.7
	Inventories, net		0			102.2			0			93.9			(0.3	)		195.8
	Deferred tax assets		0			16.4			(1.5	)		0.2			0			15.1
	Other current assets		0			8			2.8			30.1			0			40.9
	Total current assets		6.9			221.3			326.2			272.9			(346.1	)		481.2
	Equity investments		148.7			77.1			27.3			3.8			(251.1	)		5.8
	Property, plant and equipment, net		0			105.7			0			55.4			0			161.1
	Goodwill		0			39.8			0			35.8			0			75.6
	Deferred tax assets		0			33.5			(12.4	)		6.1			0			27.2
	Other noncurrent assets		0			15.8			126.7			52.5			(165.9	)		29.1
	Total assets	$	155.6		$	493.2		$	467.8		$	426.5		$	(763.1	)	$	780
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	371.7		$	17		$	60.6		$	(345.9	)	$	103.5
	Accrued liabilities		4.9			15.9			12.2			44.7			0			77.7
	Total current liabilities		5			387.6			29.2			105.3			(345.9	)		181.2
	Long-term debt		0			397.6			0			64.4			(165.9	)		296.1
	Other long-term liabilities		0			101.2			2.4			31			0			134.6
	Total liabilities		5			886.4			31.6			200.7			(511.8	)		611.9
	Koppers shareholders’ equity		150.6			(393.2	)		436.2			208.3			(251.3	)		150.6
	Noncontrolling interests		0			0			0			17.5			0			17.5
	Total liabilities and equity	$	155.6		$	493.2		$	467.8		$	426.5		$	(763.1	)	$	780
Condensed Consolidating Statement of Cash Flows	'
	Condensed Consolidating Statement of Cash Flows
	For the Nine Months Ended September 30, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	32.6		$	39.7		$	0		$	16.8		$	(23.5	)	$	65.6
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(13.3	)		0			(16.1	)		0			(29.4	)
	Net cash proceeds (payments) from divestitures and asset sales		0			1.4			0			1			0			2.4
	Net cash provided by (used in) investing activities		0			(11.9	)		0			(15.1	)		0			(27.0	)
	Cash provided by (used in) financing activities:
	Deferred financing costs		0			(1.2	)		0			0			0			(1.2	)
	Dividends paid		(15.3	)		(23.5	)		0			0			23.5			(15.3	)
	Other financing activities		0			0			0			2.3			0			2.3
	Stock issued (repurchased)		(17.3	)		0			0			0			0			(17.3	)
	Net cash provided by (used in) financing activities		(32.6	)		(24.7	)		0			2.3			23.5			(31.5	)
	Effect of exchange rates on cash		0			0.1			0			(1.5	)		0			(1.4	)
	Net increase (decrease) in cash and cash equivalents		0			3.2			0			2.5			0			5.7
	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		$	8		$	0		$	64.4		$	0		$	72.4
	Condensed Consolidating Statement of Cash Flows
	For the Nine Months Ended September 30, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	21.8		$	32		$	0		$	15.5		$	(14.8	)	$	54.5
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(12.2	)		0			(3.6	)		0			(15.8	)
	Net cash proceeds (payments) from divestitures and asset sales		0			0.3			0			0.4			0			0.7
	Net cash provided by (used in) investing activities		0			(11.9	)		0			(3.2	)		0			(15.1	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of long-term debt		0.1			(5.0	)		0			(0.1	)		0			(5.0	)
	Deferred financing costs		0			(0.1	)		0			0			0			(0.1	)
	Stock issued (repurchased)		(7.4	)		0			0			0			0			(7.4	)
	Dividends paid		(14.5	)		(14.8	)		0			0			14.8			(14.5	)
	Net cash provided by (used in) financing activities		(21.8	)		(19.9	)		0			(0.1	)		14.8			(27.0	)
	Effect of exchange rates on cash		0			(0.1	)		0			2.5			0			2.4
	Net increase (decrease) in cash and cash equivalents		0			0.1			0			14.7			0			14.8
	Cash and cash equivalents at beginning of year		0			0			0			54.1			0			54.1
	Cash and cash equivalents at end of period	$	0		$	0.1		$	0		$	68.8		$	0		$	68.9

Subsidiary_Guarantor_Informati3

Subsidiary Guarantor Information for Shelf Registration (Tables)	9 Months Ended
	Sep. 30, 2013
Text Block [Abstract]	'
Condensed Consolidating Statement of Comprehensive Income	'
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	230.1		$	11.9		$	120.7		$	43.4		$	(10.9	)	$	395.2
	Cost of sales including depreciation and amortization		0			197.5			7.2			103.6			40.5			(11.0	)		337.8
	Selling, general and administrative		0.5			10.8			0.1			5.5			1.4			0			18.3
	Operating profit (loss)		(0.5	)		21.8			4.6			11.6			1.5			0.1			39.1
	Other income (expense)		19.4			0.4			1.1			0.7			0.1			(20.4	)		1.3
	Interest expense (income)		0			6.7			0.2			0.6			0.2			(1.0	)		6.7
	Income taxes		(0.2	)		10.2			0			3.8			0.3			0			14.1
	Income from continuing operations		19.1			5.3			5.5			7.9			1.1			(19.3	)		19.6
	Discontinued operations		0			0			0			(0.1	)		0			0			(0.1	)
	Noncontrolling interests		0			0			0			0			0.4			0			0.4
	Net income attributable to Koppers	$	19.1		$	5.3		$	5.5		$	7.8		$	0.7		$	(19.3	)	$	19.1
	Comprehensive income attributable to Koppers	$	25.8		$	6.4		$	5.7		$	13.2		$	1.3		$	(26.6	)	$	25.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2012
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	238.2		$	15.1		$	118.6		$	29.2		$	(13.2	)	$	387.9
	Cost of sales including depreciation and amortization					211			9.3			102.3			27.4			(11.9	)		338.1
	Selling, general and administrative		0.4			11.6			0.4			5.6			1			0			19
	Operating profit (loss)		(0.4	)		15.6			5.4			10.7			0.8			(1.3	)		30.8
	Other income (expense)		16.3			0.4			0.3			0.1			(0.2	)		(16.3	)		0.6
	Interest expense (income)		0.1			6.9			0			1			0.2			(1.3	)		6.9
	Income taxes		(0.2	)		7			0.1			1.4			0			0			8.3
	Income from continuing operations		16			2.1			5.6			8.4			0.4			(16.3	)		16.2
	Discontinued operations		0			0			0			0			0			0			0
	Noncontrolling interests		0			0			0			0			0.2			0			0.2
	Net income attributable to Koppers	$	16		$	2.1		$	5.6		$	8.4		$	0.2		$	(16.3	)	$	16
	Comprehensive income attributable to Koppers	$	25		$	3.3		$	8.1		$	14.3		$	0.4		$	(26.1	)	$	25
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	660.3		$	48.5		$	348.6		$	123.9		$	(44.8	)	$	1,136.50
	Cost of sales including depreciation and amortization		0			580.6			34.3			305.7			116.1			(44.9	)		991.8
	Selling, general and administrative		1.5			29.7			0.7			16.8			3.5			0			52.2
	Operating profit (loss)		(1.5	)		50			13.5			26.1			4.3			0.1			92.5
	Other income (expense)		45.4			1.3			6.3			0.8			0.7			(51.7	)		2.8
	Interest expense (income)		0			20.2			0.1			2.5			0.6			(3.2	)		20.2
	Income taxes		(0.6	)		21.3			0.2			7.4			1			0			29.3
	Income from continuing operations		44.5			9.8			19.5			17			3.4			(48.4	)		45.8
	Discontinued operations		0			0			0			(0.1	)		0			0			(0.1	)
	Noncontrolling interests		0			0			0			0			1.2			0			1.2
	Net income attributable to Koppers	$	44.5		$	9.8		$	19.5		$	16.9		$	2.2		$	(48.4	)	$	44.5
	Comprehensive income attributable to Koppers	$	40.8		$	13		$	12.9		$	14.4		$	2.8		$	(43.1	)	$	40.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2012
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	689.1		$	73		$	355.4		$	111.3		$	(48.7	)	$	1,180.10
	Cost of sales including depreciation and amortization		0			601.9			49.2			309.6			103.3			(39.7	)		1,024.30
	Selling, general and administrative		1.3			33			1.6			16.7			2.5			0			55.1
Operating profit (loss)		(1.3	)		54.2			22.2			29.1			5.5			(9.0	)		100.7
Other income (expense)		52.9			0.4			0.8			0.1			0.4			(52.9	)		1.7
Interest expense (income)		0.1			20.7			0			3			0.9			(3.9	)		20.8
Income taxes		(0.5	)		20.5			0.3			7.5			0.7			0			28.5
Income from continuing operations		52			13.4			22.7			18.7			4.3			(58.0	)		53.1
Discontinued operations		0			0			0			(0.1	)		0			0			(0.1	)
Noncontrolling interests		0			0			0			0			1			0			1
Net income attributable to Koppers	$	52		$	13.4		$	22.7		$	18.6		$	3.3		$	(58.0	)	$	52
Comprehensive income attributable to Koppers	$	59.8		$	16.9		$	24.9		$	21.4		$	3.3		$	(66.5	)	$	59.8
Condensed Consolidating Balance Sheet	'
	Condensed Consolidating Balance Sheet
	September 30, 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		$	8		$	0		$	48.3		$	16.1		$	0		$	72.4
	Restricted cash		0			0			1.5			0			0			0			1.5
	Accounts receivable, net		6.7			100.1			339.8			58.7			34.2			(357.4	)		182.1
	Inventories, net		0			79.5			0			79.9			7.2			(0.2	)		166.4
	Deferred tax assets		0			16.2			(1.5	)		0			0			0			14.7
	Other current assets		0			6.5			1.8			10.6			16.2			0			35.1
	Total current assets		6.7			210.3			341.6			197.5			73.7			(357.6	)		472.2
	Equity investments		161.3			80.8			27.3			36.4			4.2			(303.8	)		6.2
	Property, plant and equipment, net		0			105.1			0			41			23.3			0			169.4
	Goodwill		0			39.8			0			32.3			1.3			0			73.4
	Deferred tax assets		0			20.1			(12.4	)		6.5			(1.6	)		0			12.6
	Other noncurrent assets		0.1			15.6			120.2			10.4			41.1			(160.1	)		27.3
	Total assets	$	168.1		$	471.7		$	476.7		$	324.1		$	142		$	(821.5	)	$	761.1
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	384.3		$	14.7		$	32.9		$	20.3		$	(357.4	)	$	94.9
	Accrued liabilities		4.6			17.1			10.5			30.3			9.6			0			72.1
	Total current liabilities		4.7			401.4			25.2			63.2			29.9			(357.4	)		167
	Long-term debt		0			398.5			0			57.9			0			(160.0	)		296.4
	Other long-term liabilities		0			81.1			2.4			22.7			6.8			0			113
	Total liabilities		4.7			881			27.6			143.8			36.7			(517.4	)		576.4
	Koppers shareholders’ equity		163.4			(409.3	)		449.1			180.3			84			(304.1	)		163.4
	Noncontrolling interests		0			0			0			0			21.3			0			21.3
	Total liabilities and equity	$	168.1		$	471.7		$	476.7		$	324.1		$	142		$	(821.5	)	$	761.1
	Condensed Consolidating Balance Sheet
	December 31, 2012
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	4.8		$	0		$	40.7		$	21.2		$	0		$	66.7
	Receivables, net		6.9			89.9			324.9			65.9			21.2			(346.1	)		162.7
	Inventories, net		0			102.2			0			86.7			7.2			(0.3	)		195.8
	Deferred tax assets		0			16.4			(1.5	)		0			0.2			0			15.1
	Other current assets		0			8			2.8			17.6			12.5			0			40.9
	Total current assets		6.9			221.3			326.2			210.9			62.3			(346.4	)		481.2
	Equity investments		148.7			77.1			27.3			30.2			3.8			(281.3	)		5.8
	Property, plant and equipment, net		0			105.7			0			40.7			14.7			0			161.1
	Goodwill		0			39.8			0			34.4			1.4			0			75.6
	Deferred tax assets		0			33.5			(12.4	)		7.6			(1.5	)		0			27.2
	Other noncurrent assets		0			15.8			126.7			12.1			40.3			(165.8	)		29.1
	Total assets	$	155.6		$	493.2		$	467.8		$	335.9		$	121		$	(793.5	)	$	780
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	371.7		$	17		$	42.2		$	18.6		$	(346.1	)	$	103.5
	Accrued liabilities		4.9			15.9			12.2			35.7			9			0			77.7
	Total current liabilities		5			387.6			29.2			77.9			27.6			(346.1	)		181.2
	Long-term debt		0			397.6			0			64.4			0			(165.9	)		296.1
	Other long-term liabilities		0			101.2			2.4			24.5			6.5			0			134.6
	Total liabilities		5			886.4			31.6			166.8			34.1			(512.0	)		611.9
	Koppers shareholders’ equity		150.6			(393.2	)		436.2			169.1			69.4			(281.5	)		150.6
	Noncontrolling interests		0			0			0			0			17.5			0			17.5
	Total liabilities and equity	$	155.6		$	493.2		$	467.8		$	335.9		$	121		$	(793.5	)	$	780
Condensed Consolidating Statement of Cash Flows	'
	Condensed Consolidating Statement of Cash Flows
	For the Nine Months Ended September 30, 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	$	32.6		$	39.7		$	0		$	14.9		$	1.9		$	(23.5	)	$	65.6
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(13.3	)		0			(6.6	)		(9.5	)		0			(29.4	)
	Net cash proceeds (payments) from divestitures and asset sales		0			1.4			0			1.1			(0.1	)		0			2.4
	Net cash provided by (used in) investing activities		0			(11.9	)		0			(5.5	)		(9.6	)		0			(27.0	)
	Cash provided by (used in) financing activities:
	Deferred financing costs		0			(1.2	)		0			0			0			0			(1.2	)
	Dividends paid		(15.3	)		(23.5	)		0			0			0			23.5			(15.3	)
	Other financing activities		0			0			0			0			2.3			0			2.3
	Stock issued (repurchased)		(17.3	)		0			0			0			0			0			(17.3	)
	Net cash provided by (used in) financing activities		(32.6	)		(24.7	)		0			0			2.3			23.5			(31.5	)
	Effect of exchange rates on cash		0			0.1			0			(1.8	)		0.3			0			(1.4	)
	Net increase (decrease) in cash and cash equivalents		0			3.2			0			7.6			(5.1	)		0			5.7
	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		$	8		$	0		$	48.3		$	16.1		$	0		$	72.4
	Condensed Consolidating Statement of Cash Flows
	For the Nine Months Ended September 30, 2012
		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	$	21.8		$	32		$	0		$	21.5		$	(6.0	)	$	(14.8	)	$	54.5
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(12.2	)		0			(3.2	)		(0.4	)		0			(15.8	)
	Net cash proceeds (payments) from divestitures and asset sales		0			0.3			0			0.3			0.1			0			0.7
	Net cash provided by (used in) investing activities		0			(11.9	)		0			(2.9	)		(0.3	)		0			(15.1	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of long-term debt		0.1			(5.0	)		0			0			(0.1	)		0			(5.0	)
	Deferred financing costs		0			(0.1	)		0			0			0			0			(0.1	)
	Stock issued (repurchased)		(7.4	)		0			0			0			0			0			(7.4	)
	Dividends paid		(14.5	)		(14.8	)		0			0			0			14.8			(14.5	)
	Net cash provided by (used in) financing activities		(21.8	)		(19.9	)		0			0			(0.1	)		14.8			(27.0	)
	Effect of exchange rates on cash		0			(0.1	)		0			2.5			0			0			2.4
	Net increase (decrease) in cash and cash equivalents		0			0.1			0			21.1			(6.4	)		0			14.8
	Cash and cash equivalents at beginning of year		0			0			0			45.1			9			0			54.1
	Cash and cash equivalents at end of period	$	0		$	0.1		$	0		$	66.2		$	2.6		$	0		$	68.9

Dividends_Additional_Informati

Dividends - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Equity [Abstract]	'	'	'	'
Dividends declared per common share	$0.25	$0.24	$0.75	$0.72
Common share, dividend payable date	6-Jan-14	'	'	'
Common share, dividend declared date	6-Nov-13	'	'	'
Common share, dividend record date	18-Nov-13	'	'	'

Discontinued_Operations_Additi

Discontinued Operations - Additional Information (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Discontinued Operations And Disposal Groups [Abstract]	'
Estimated total future closure costs	$0.30
Future completion period, closure	'2015

Discontinued_Operations_Summar

Discontinued Operations - Summary of Restructuring Activities and Related Reserves (Detail) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	$12.90	$15.90
Charges	'	0.5
Costs charged against assets	'	-0.4
Reversal of accrued charges	-0.4	-0.6
Cash expenditures	-1.6	-2.7
Currency translation	-1.2	0.2
Reserve, Ending Balance	9.7	12.9
Severance and Employee Benefits [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	0.2	1.8
Charges	'	0.1
Costs charged against assets	'	0
Reversal of accrued charges	-0.1	0
Cash expenditures	0	-1.7
Currency translation	0	0
Reserve, Ending Balance	0.1	0.2
Environmental Remediation [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	6.7	6.7
Charges	'	0
Costs charged against assets	'	0
Reversal of accrued charges	0	0
Cash expenditures	-0.1	-0.1
Currency translation	-0.7	0.1
Reserve, Ending Balance	5.9	6.7
Inventory Writedowns [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	0	0
Charges	'	0.4
Costs charged against assets	'	-0.4
Reversal of accrued charges	0	0
Cash expenditures	0	0
Currency translation	0	0
Reserve, Ending Balance	0	0
Site Demolition [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	5.9	6.2
Charges	'	0
Costs charged against assets	'	0
Reversal of accrued charges	-0.3	0
Cash expenditures	-1.5	-0.4
Currency translation	-0.5	0.1
Reserve, Ending Balance	3.6	5.9
Other [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	0.1	1.2
Charges	'	0
Costs charged against assets	'	0
Reversal of accrued charges	0	-0.6
Cash expenditures	0	-0.5
Currency translation	0	0
Reserve, Ending Balance	$0.10	$0.10

Discontinued_Operations_Summar1

Discontinued Operations - Summary of Net Sales and Operating Profit from Discontinued Operations (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Discontinued Operations And Disposal Groups [Abstract]	'	'	'	'
Net sales	$0	$0.30	$0	$5.70
Operating loss	($0.10)	($0.10)	($0.20)	($0.30)

Fair_Value_Measurements_Schedu

Fair Value Measurements - Schedule of Company's Financial Instruments (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Fair Value [Member]	'	'
Financial assets:	'	'
Cash and cash equivalents, including restricted cash	$73.90	$66.70
Investments and other assets	1.4	1.4
Financial liabilities:	'	'
Long-term debt	325.3	331.1
Carrying Value [Member]	'	'
Financial assets:	'	'
Cash and cash equivalents, including restricted cash	73.9	66.7
Investments and other assets	1.4	1.4
Financial liabilities:	'	'
Long-term debt	$296.40	$296.10

Comprehensive_Income_and_Equit2

Comprehensive Income and Equity - Schedule of Comprehensive Income (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Equity [Abstract]	'	'	'	'
Net income	$19.50	$16.20	$45.70	$53
Other comprehensive income (loss):	'	'	'	'
Change in currency translation adjustment	5.6	5.3	-0.4	1.9
Change in foreign currency transactions of long-term subsidiary investments	0.3	2.5	-6.6	2.2
Change in unrecognized pension transition asset, net of tax benefit of $0.0, $0.1, $0.0 and $0.1	0	-0.1	0	-0.2
Change in unrecognized prior service cost, net of tax expense of $0.0, $0.0, $0.0 and $0.0	0	0.1	0.1	0.1
Change in unrecognized pension net loss, net of tax expense of $0.8, $0.8, $2.3 and $2.3	1.2	1.3	3.5	3.8
Total comprehensive income	26.6	25.3	42.3	60.8
Less: comprehensive income attributable to noncontrolling interests	0.8	0.3	1.5	1
Comprehensive income attributable to Koppers	$25.80	$25	$40.80	$59.80

Comprehensive_Income_and_Equit3

Comprehensive Income and Equity - Schedule of Comprehensive Income (Parenthetical) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Equity [Abstract]	'	'	'	'
Tax expense, unrecognized pension transition asset	$0	$0.10	$0	$0.10
Tax expense, unrecognized prior service cost	0	0	0	0
Tax expense, unrecognized pension net loss	$0.80	$0.80	$2.30	$2.30

Comprehensive_Income_and_Equit4

Comprehensive Income and Equity - Schedule of Change in Equity (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Comprehensive Income And Equity [Line Items]	'	'	'	'
Balance	'	'	$168.10	$107.20
Net income	19.5	16.2	45.7	53
Issuance of common stock	'	'	0.2	0.8
Employee stock plans	'	'	5.2	5.4
Other comprehensive income (loss)	'	'	-3.4	7.8
Dividends	'	'	-15.9	-15.2
Investment in noncontrolling interests	'	'	2.3	'
Repurchases of common stock	'	'	-17.5	-8.2
Balance	184.7	150.8	184.7	150.8
Total Koppers Shareholders' Equity [Member]	'	'	'	'
Comprehensive Income And Equity [Line Items]	'	'	'	'
Balance	'	'	150.6	94.8
Net income	'	'	44.5	52
Issuance of common stock	'	'	0.2	0.8
Employee stock plans	'	'	5.2	5.4
Other comprehensive income (loss)	'	'	-3.7	7.8
Dividends	'	'	-15.9	-15.2
Investment in noncontrolling interests	'	'	0	'
Repurchases of common stock	'	'	-17.5	-8.2
Balance	163.4	137.4	163.4	137.4
Noncontrolling Interests [Member]	'	'	'	'
Comprehensive Income And Equity [Line Items]	'	'	'	'
Balance	'	'	17.5	12.4
Net income	'	'	1.2	1
Issuance of common stock	'	'	0	0
Employee stock plans	'	'	0	0
Other comprehensive income (loss)	'	'	0.3	0
Dividends	'	'	0	0
Investment in noncontrolling interests	'	'	2.3	'
Repurchases of common stock	'	'	0	0
Balance	$21.30	$13.40	$21.30	$13.40

Earnings_Per_Common_Share_Sche

Earnings Per Common Share - Schedule of Basic and Diluted Earnings Per Common Share (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]	'	'	'	'
Net income attributable to Koppers	$19.10	$16	$44.50	$52
Less: loss from discontinued operations	-0.1	0	-0.1	-0.1
Income from continuing operations attributable to Koppers	$19.20	$16	$44.60	$52.10
Weighted average common shares outstanding:	'	'	'	'
Basic	20,577	20,694	20,657	20,709
Effect of dilutive securities	224	206	230	231
Diluted	20,801	20,900	20,887	20,940
Earnings per common share - continuing operations:	'	'	'	'
Basic earnings per common share	$0.93	$0.77	$2.16	$2.52
Diluted earnings per common share	$0.92	$0.77	$2.13	$2.50
Other data:	'	'	'	'
Antidilutive securities excluded from computation of diluted earnings per common share	254	203	236	191

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	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	'
Stock options, term in years	'10 years	'
Future compensation expense related to non-vested stock-based compensation arrangements	8	'
Future compensation expense, weighted-average expected period of recognition in months	'21 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	'

StockBased_Compensation_Summar

Stock-Based Compensation - Summary of Performance Stock Units (Detail)	Sep. 30, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	481,625	404,775
Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	328,098	268,677
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	'
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	98,453	'
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	95,858	'
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	147,680	'
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	143,787	'

StockBased_Compensation_Summar1

Stock-Based Compensation - Summary of Status and Activity of Non-Vested Stock Awards (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	404,775
Granted	159,594
Credited from dividends	10,590
Performance stock unit adjustment	43,921
Vested	-132,112
Forfeited	-5,143
Non-vested, Ending Balance	481,625
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit	$36.11
Granted, Weighted Average Grant Date Fair Value per Unit	$42.64
Credited from dividends, Weighted Average Grant Date Fair Value per Unit	$35.17
Performance stock unit adjustment, Weighted Average Grant Date Fair Value per Unit	$40.09
Vested, Weighted Average Grant Date Fair Value per Unit	$29.81
Forfeited, Weighted Average Grant Date Fair Value per Unit	$40.34
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit	$40.29
Restricted Stock Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	136,098
Granted	62,276
Credited from dividends	3,526
Performance stock unit adjustment	0
Vested	-46,314
Forfeited	-2,059
Non-vested, Ending Balance	153,527
Performance Stock Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	268,677
Granted	97,318
Credited from dividends	7,064
Performance stock unit adjustment	43,921
Vested	-85,798
Forfeited	-3,084
Non-vested, Ending Balance	328,098

StockBased_Compensation_Stock_

Stock-Based Compensation - Stock Options Fair Value Assumptions (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
February 2013 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 2012 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
February 2011 Grant [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Grant date price per share of option award	$40.26
Expected dividend yield per share	2.50%
Expected life in years	'6 years 6 months
Expected volatility	60.00%
Risk-free interest rate	3.02%
Grant date fair value per share of option awards	$19.28

StockBased_Compensation_Summar2

Stock-Based Compensation - Summary of Status and Activity of Stock Options (Detail) (USD $)	9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Options Outstanding, Beginning Balance	331,799
Options, Granted	94,532
Options, Exercised	-5,251
Options Outstanding, Ending Balance	421,080
Options Exercisable, Ending Balance	167,565
Outstanding, Weighted Average Exercise Price per Option, Beginning Balance	$34.07
Granted, Weighted Average Exercise Price per Option	$42.76
Exercised, Weighted Average Exercise Price per Option	$39.04
Outstanding, Weighted Average Exercise Price per Option, Ending Balance	$35.96
Exercisable, Weighted Average Exercise Price per Option, Ending Balance	$29.15
Outstanding at September 30, 2013, Weighted Average Remaining Contractual Term	'7 years 1 month 10 days
Exercisable at September 30, 2013, Weighted Average Remaining Contractual Term	'4 years 11 months 9 days
Outstanding at September 30, 2013, Aggregate Intrinsic Value	$2.80
Exercisable at September 30, 2013, Aggregate Intrinsic Value	$2.30

StockBased_Compensation_Schedu

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Stock-based compensation expense recognized:	'	'	'	'
Selling, general and administrative expenses	$1.90	$1.90	$4.70	$5.10
Less related income tax benefit	0.8	0.8	1.9	2
Total stock-based compensation expense recognized	$1.10	$1.10	$2.80	$3.10

Segment_Information_Additional

Segment Information - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
	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		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues from external customers:	'	'	'	'
Revenues from external customers	$395.20	$387.90	$1,136.50	$1,180.10
Intersegment revenues:	'	'	'	'
Intersegment revenues	395.2	387.9	1,136.50	1,180.10
Depreciation and amortization expense:	'	'	'	'
Depreciation and amortization expense	7.2	6.7	21.8	21.1
Operating profit:	'	'	'	'
Operating profit (loss)	39.1	30.8	92.5	100.7
Operating Segments [Member] | Carbon Materials and Chemicals [Member]	'	'	'	'
Revenues from external customers:	'	'	'	'
Revenues from external customers	241.6	241.1	692.4	757.3
Intersegment revenues:	'	'	'	'
Intersegment revenues	241.6	241.1	692.4	757.3
Depreciation and amortization expense:	'	'	'	'
Depreciation and amortization expense	4.5	4.2	13.5	12.8
Operating profit:	'	'	'	'
Operating profit (loss)	21.8	18.4	47.4	65.1
Operating Segments [Member] | Railroad and Utility Products [Member]	'	'	'	'
Revenues from external customers:	'	'	'	'
Revenues from external customers	153.6	146.8	444.1	422.8
Intersegment revenues:	'	'	'	'
Intersegment revenues	153.6	146.8	444.1	422.8
Depreciation and amortization expense:	'	'	'	'
Depreciation and amortization expense	2.7	2.5	8.3	8.3
Operating profit:	'	'	'	'
Operating profit (loss)	17.8	12.8	46.6	36.9
Intersegment [Member] | Carbon Materials and Chemicals [Member]	'	'	'	'
Revenues from external customers:	'	'	'	'
Revenues from external customers	23.3	27	70.9	83.8
Intersegment revenues:	'	'	'	'
Intersegment revenues	23.3	27	70.9	83.8
Corporate, Non-Segment [Member]	'	'	'	'
Operating profit:	'	'	'	'
Operating profit (loss)	($0.50)	($0.40)	($1.50)	($1.30)

Segment_Information_Summary_of1

Segment Information - Summary of Tangible and Intangible Assets by Segment (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Segment assets:	'	'
Segment assets	$761.10	$780
Goodwill:	'	'
Goodwill	73.4	75.6
Carbon Materials and Chemicals [Member]	'	'
Segment assets:	'	'
Segment assets	531.2	516.3
Goodwill:	'	'
Goodwill	68.5	70.2
Railroad and Utility Products and Services [Member]	'	'
Segment assets:	'	'
Segment assets	181.5	205
Goodwill:	'	'
Goodwill	4.9	5.4
All Other [Member]	'	'
Segment assets:	'	'
Segment assets	$48.40	$58.70

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Income Tax Disclosure [Abstract]	'	'	'	'	'
Percentage of pretax income	46.40%	35.20%	43.00%	34.70%	'
Potential income tax examination	$0	'	$0	'	'
Net tax benefit included in income taxes, discrete items	1.6	0.3	3	0.2	'
U.S. federal statutory rate	35.00%	35.00%	35.00%	35.00%	'
Taxes on foreign earnings	10.20%	'	6.60%	-1.50%	'
State taxes	1.80%	1.60%	1.80%	1.60%	'
Tax credit	-0.20%	'	'	'	'
Uncertain tax position	0.90%	'	0.80%	'	'
Nondeductible expenses	0.50%	0.40%	0.50%	0.70%	'
Domestic manufacturing deduction	-1.80%	-2.50%	-1.70%	-1.90%	'
Unrecognized tax benefits	'	0.70%	'	0.80%	'
Unrecognized tax benefits with impact on the effective tax rate	4.4	'	4.4	'	5.5
Unrecognized tax benefits	6.8	'	6.8	'	7.7
Accrued interest expense and penalties	$1.10	'	$1.10	'	$1.30

Inventories_Components_of_Inve

Inventories - Components of Inventories (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Inventory Disclosure [Abstract]	'	'
Raw materials	$103	$118.20
Work in process	18.3	20
Finished goods	100.1	109.7
Inventories, gross	221.4	247.9
Less revaluation to LIFO	55	52.1
Net	$166.40	$195.80

Property_Plant_and_Equipment_P

Property, Plant and Equipment - Property, Plant and Equipment (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	$684.20	$660
Less accumulated depreciation	514.8	498.9
Net	169.4	161.1
Land [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	9.2	7
Buildings [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	35.7	36.4
Machinery and Equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	$639.30	$616.60

Property_Plant_and_Equipment_A

Property, Plant and Equipment - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended			1 Months Ended	12 Months Ended		1 Months Ended
In Millions, unless otherwise specified	Feb. 29, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Nov. 30, 2011	Oct. 31, 2013	Dec. 31, 2012	Sep. 30, 2013	Oct. 31, 2013
	T						Subsequent Event [Member]	Koppers Carbon and Chemical Company Limited [Member]	Koppers Carbon and Chemical Company Limited [Member]	Koppers Carbon and Chemical Company Limited [Member]
							Battery			Subsequent Event [Member]
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'	'	'	'	'
Liquid carbon pitch leaked from storage tank	400	'	'	'	'	'	'	'	'	'
Costs associated with leak	'	'	$1.30	'	$3.70	'	'	'	'	'
Insurance recoveries associated with the leak, net	'	0.2	'	1.2	'	'	'	'	'	'
Percentage of operations in Tangshan, China of owned subsidiary	'	'	'	'	'	'	'	'	'	60.00%
Number of coke batteries to be closed	'	'	'	'	'	'	2	'	'	'
Profit after deduction of profit attributable to non-controlling interests	'	'	'	'	'	'	'	3.5	'	'
Book value of fixed assets	'	'	'	'	'	'	'	'	$15	'
Supply of export commitments	'	30.00%	'	30.00%	'	30.00%	'	'	'	'

Pensions_and_Postretirement_Be2

Pensions and Postretirement Benefit Plans - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
	Plans
Postemployment Benefits [Abstract]	'
Number of domestic non qualified defined benefit plan	3

Pensions_and_Postretirement_Be3

Pensions and Postretirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Postemployment Benefits [Abstract]	'	'	'	'
Service cost	$0.90	$0.80	$2.60	$2.60
Interest cost	2.7	2.8	8	8
Expected return on plan assets	-3.2	-2.7	-9.5	-8
Amortization of prior service cost	0	0	0.1	0.1
Amortization of net loss	1.9	2	5.7	6.1
Amortization of transition asset	0	0	0	-0.2
Net periodic benefit cost	2.3	2.9	6.9	8.6
Defined contribution plan expense	1.2	1.1	4.1	3.8
Multi-employer pension plan expense	0.1	0.1	0.3	0.3
Other postretirement benefit plans	$0.10	$0.20	$0.40	$0.50

Debt_Schedule_of_LongTerm_Debt

Debt - Schedule of Long-Term Debt Instruments (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Proforma Debt Instrument [Line Items]	'	'
Total debt	$296.40	$296.10
Less short term debt and current maturities of long-term debt	0	0
Long-term debt	296.4	296.1
Revolving Credit Facility [Member]	'	'
Proforma Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	0.00%	'
Debt, Maturity	'2018	'
Revolving Credit Facility	0	0
Senior Notes [Member]	'	'
Proforma Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	7.88%	'
Debt, Maturity	'2019	'
Senior Notes	296.4	296.1
Long-term debt	$296.40	$296.10

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)	9 Months Ended		1 Months Ended	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 01, 2009	Mar. 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
	Senior Notes [Member]	Senior Notes [Member]	Revolving Credit Facility [Member]	Revolving Credit Facility [Member]	Revolving Credit Facility [Member]	Revolving Credit Facility [Member]	Revolving Credit Facility [Member]
Debt Instrument [Line Items]	'	'	'	'	'	'	'
Line of credit facility, borrowing capacity	'	'	'	$300	'	$300	'
Line of credit facility, commitment fees	'	'	'	0.3	0.2	0.8	0.7
Extended revolving credit maturity date	'	'	27-Mar-18	'	'	'	'
Debt instrument, unused borrowing capacity	'	'	'	286.9	'	286.9	'
Letters of credit, amount outstanding	'	'	'	9.1	'	9.1	'
Debt, Weighted Average Interest Rate	7.88%	'	'	0.00%	'	0.00%	'
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%	'	'	'	'	'	'

Asset_Retirement_Obligations_S

Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligation (Detail) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Asset Retirement Obligation Disclosure [Abstract]	'	'
Balance at beginning of year	$21.50	$21.30
Accretion expense	0.8	1.1
Revision in estimated cash flows, net	0	1.8
Cash expenditures	-4.1	-3
Currency translation	-0.5	0.3
Balance at end of period	$17.70	$21.50

Deferred_Revenue_from_Extended2

Deferred Revenue from Extended Product Warranty Liabilities - Deferred Revenue from Extended Product Warranty Liabilities (Detail) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Revenue Recognition [Abstract]	'	'
Balance at beginning of year	$3.90	$4.80
Revenue earned	-0.5	-0.9
Balance at end of period	$3.40	$3.90

Commitments_and_Contingent_Lia2

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

1 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

Jul. 31, 2012

Jul. 31, 2004

Sep. 30, 2013

Sep. 30, 2012

Dec. 31, 2012

Mar. 30, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2011

State

Plaintiff

site

Compensatory Damages [Member]

Punitive Damages [Member]

Pennsylvania [Member]

Arkansas [Member]

Tennessee [Member]

Australia [Member]

Australia [Member]

site

Cases

Cases

Cases

Cases

Cases

Cases

Plaintiff

Cases

Commitments And Contingent Liabilities [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of states new claims filed

'

'

3

'

'

'

'

'

'

'

'

'

'

Number of plaintiffs

'

'

110

'

136

'

'

'

'

'

'

'

'

Number of cases

'

'

60

'

75

'

60

55

56

3

1

'

'

Compensatory damages

'

'

'

$1,700,000

'

'

'

'

'

$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

'

'

'

'

16,000,000

'

'

'

'

'

'

'

'

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

'

'

600,000

'

'

'

'

'

'

'

'

'

'

Environmental remediation expense

'

'

'

'

'

'

'

'

'

'

'

5,900,000

1,600,000

Amount contributable by third party

'

'

'

'

'

'

'

'

'

'

'

'

7,500,000

Environmental remediation reserve

'

'

1,000,000

'

1,000,000

'

'

'

'

'

'

'

4,300,000

Net amount contributed by third party

'

'

'

'

'

'

'

'

'

'

'

2,800,000

'

Accrued liability for environmental matters, current

'

'

7,900,000

8,500,000

'

'

'

'

'

'

'

'

'

Reversal of reserve includes sale to unaffiliated third party

'

'

$1,100,000

'

'

'

'

'

'

'

'

'

'

Commitments_and_Contingent_Lia3

Commitments and Contingent Liabilities - Changes in Accrued Liability for Environmental Matters (Detail) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Commitments And Contingencies Disclosure [Abstract]	'	'
Balance at beginning of year	$14.10	$17.70
Expense	1	1
Reversal of reserves	-1.2	-0.4
Cash expenditures	-0.8	-4.6
Currency translation	-1.3	0.4
Balance at end of year	$11.80	$14.10

Subsidiary_Guarantor_Informati4

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Additional Information (Detail) (Senior Notes [Member], USD $)	Dec. 01, 2009
In Millions, unless otherwise specified
Senior Notes [Member]	'
Debt Instrument [Line Items]	'
Principal value of Senior Notes	$300
Percent-owned material domestic subsidiaries	100.00%

Subsidiary_Guarantor_Informati5

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Statement of Comprehensive Income (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	$395.20	$387.90	$1,136.50	$1,180.10
Selling, general and administrative	18.3	19	52.2	55.1
Operating profit (loss)	39.1	30.8	92.5	100.7
Other income (expense)	1.3	0.6	2.8	1.7
Interest expense (income)	6.7	6.9	20.2	20.8
Income taxes	14.1	8.3	29.3	28.5
Income from continuing operations	19.6	16.2	45.8	53.1
Discontinued operations	-0.1	0	-0.1	-0.1
Noncontrolling interests	0.4	0.2	1.2	1
Net income attributable to Koppers	19.1	16	44.5	52
Comprehensive income attributable to Koppers	25.8	25	40.8	59.8
Senior Notes [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	395.2	387.9	1,136.50	1,180.10
Cost of sales including depreciation and amortization	337.8	338.1	991.8	1,024.30
Selling, general and administrative	18.3	19	52.2	55.1
Operating profit (loss)	39.1	30.8	92.5	100.7
Other income (expense)	1.3	0.6	2.8	1.7
Interest expense (income)	6.7	6.9	20.2	20.8
Income taxes	14.1	8.3	29.3	28.5
Income from continuing operations	19.6	16.2	45.8	53.1
Discontinued operations	-0.1	0	-0.1	-0.1
Noncontrolling interests	0.4	0.2	1.2	1
Net income attributable to Koppers	19.1	16	44.5	52
Comprehensive income attributable to Koppers	25.8	25	40.8	59.8
Parent [Member] | Senior Notes [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	0	0	0	0
Cost of sales including depreciation and amortization	0	0	0	0
Selling, general and administrative	0.5	0.4	1.5	1.3
Operating profit (loss)	-0.5	-0.4	-1.5	-1.3
Other income (expense)	19.4	16.3	45.4	52.9
Interest expense (income)	0	0.1	0	0.1
Income taxes	-0.2	-0.2	-0.6	-0.5
Income from continuing operations	19.1	16	44.5	52
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	19.1	16	44.5	52
Comprehensive income attributable to Koppers	25.8	25	40.8	59.8
Koppers Inc. [Member] | Senior Notes [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	230.1	238.2	660.3	689.1
Cost of sales including depreciation and amortization	197.5	211	580.6	601.9
Selling, general and administrative	10.8	11.6	29.7	33
Operating profit (loss)	21.8	15.6	50	54.2
Other income (expense)	0.4	0.4	1.3	0.4
Interest expense (income)	6.7	6.9	20.2	20.7
Income taxes	10.2	7	21.3	20.5
Income from continuing operations	5.3	2.1	9.8	13.4
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	5.3	2.1	9.8	13.4
Comprehensive income attributable to Koppers	6.4	3.3	13	16.9
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	11.9	15.1	48.5	73
Cost of sales including depreciation and amortization	7.2	9.3	34.3	49.2
Selling, general and administrative	0.1	0.4	0.7	1.6
Operating profit (loss)	4.6	5.4	13.5	22.2
Other income (expense)	1.1	0.3	6.3	0.8
Interest expense (income)	0.2	0	0.1	0
Income taxes	0	0.1	0.2	0.3
Income from continuing operations	5.5	5.6	19.5	22.7
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	5.5	5.6	19.5	22.7
Comprehensive income attributable to Koppers	5.7	8.1	12.9	24.9
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	164	147.8	470	466.7
Cost of sales including depreciation and amortization	144	129.7	419.3	412.9
Selling, general and administrative	6.9	6.6	20.3	19.2
Operating profit (loss)	13.1	11.5	30.4	34.6
Other income (expense)	0.8	-0.1	1.5	0.5
Interest expense (income)	0.8	1.2	3.1	3.9
Income taxes	4.1	1.4	8.4	8.2
Income from continuing operations	9	8.8	20.4	23
Discontinued operations	-0.1	0	-0.1	-0.1
Noncontrolling interests	0.4	0.2	1.2	1
Net income attributable to Koppers	8.5	8.6	19.1	21.9
Comprehensive income attributable to Koppers	13.8	13.9	18.7	24
Consolidating Adjustments [Member] | Senior Notes [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	-10.8	-13.2	-42.3	-48.7
Cost of sales including depreciation and amortization	-10.9	-11.9	-42.4	-39.7
Selling, general and administrative	0	0	0	0
Operating profit (loss)	0.1	-1.3	0.1	-9
Other income (expense)	-20.4	-16.3	-51.7	-52.9
Interest expense (income)	-1	-1.3	-3.2	-3.9
Income taxes	0	0	0	0
Income from continuing operations	-19.3	-16.3	-48.4	-58
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	-19.3	-16.3	-48.4	-58
Comprehensive income attributable to Koppers	($25.90)	($25.30)	($44.60)	($65.80)

Subsidiary_Guarantor_Informati6

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Balance Sheet (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Assets	'	'	'	'
Cash and cash equivalents	$72.40	$66.70	$68.90	$54.10
Restricted cash	1.5	0	'	'
Accounts receivable, net	182.1	162.7	'	'
Inventories, net	166.4	195.8	'	'
Deferred tax assets	14.7	15.1	'	'
Other current assets	25.6	31.4	'	'
Total current assets	472.2	481.2	'	'
Equity investments	6.2	5.8	'	'
Property, plant and equipment, net	169.4	161.1	'	'
Goodwill	73.4	75.6	'	'
Deferred tax assets	12.6	27.2	'	'
Other noncurrent assets	27.3	29.1	'	'
Total assets	761.1	780	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	94.9	103.5	'	'
Accrued liabilities	66.3	72.1	'	'
Total current liabilities	167	181.2	'	'
Long-term debt	296.4	296.1	'	'
Total liabilities	576.4	611.9	'	'
Koppers shareholders' equity	163.4	150.6	'	'
Noncontrolling interests	21.3	17.5	'	'
Total liabilities and equity	761.1	780	'	'
Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	72.4	66.7	68.9	54.1
Restricted cash	1.5	'	'	'
Accounts receivable, net	182.1	162.7	'	'
Inventories, net	166.4	195.8	'	'
Deferred tax assets	14.7	15.1	'	'
Other current assets	35.1	40.9	'	'
Total current assets	472.2	481.2	'	'
Equity investments	6.2	5.8	'	'
Property, plant and equipment, net	169.4	161.1	'	'
Goodwill	73.4	75.6	'	'
Deferred tax assets	12.6	27.2	'	'
Other noncurrent assets	27.3	29.1	'	'
Total assets	761.1	780	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	94.9	103.5	'	'
Accrued liabilities	72.1	77.7	'	'
Total current liabilities	167	181.2	'	'
Long-term debt	296.4	296.1	'	'
Other long-term liabilities	113	134.6	'	'
Total liabilities	576.4	611.9	'	'
Koppers shareholders' equity	163.4	150.6	'	'
Noncontrolling interests	21.3	17.5	'	'
Total liabilities and equity	761.1	780	'	'
Parent [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Restricted cash	0	'	'	'
Accounts receivable, net	6.7	6.9	'	'
Inventories, net	0	0	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	6.7	6.9	'	'
Equity investments	161.3	148.7	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Other noncurrent assets	0.1	0	'	'
Total assets	168.1	155.6	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0.1	0.1	'	'
Accrued liabilities	4.6	4.9	'	'
Total current liabilities	4.7	5	'	'
Long-term debt	0	0	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	4.7	5	'	'
Koppers shareholders' equity	163.4	150.6	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	168.1	155.6	'	'
Koppers Inc. [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	8	4.8	0.1	0
Restricted cash	0	'	'	'
Accounts receivable, net	100.1	89.9	'	'
Inventories, net	79.5	102.2	'	'
Deferred tax assets	16.2	16.4	'	'
Other current assets	6.5	8	'	'
Total current assets	210.3	221.3	'	'
Equity investments	80.8	77.1	'	'
Property, plant and equipment, net	105.1	105.7	'	'
Goodwill	39.8	39.8	'	'
Deferred tax assets	20.1	33.5	'	'
Other noncurrent assets	15.6	15.8	'	'
Total assets	471.7	493.2	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	384.3	371.7	'	'
Accrued liabilities	17.1	15.9	'	'
Total current liabilities	401.4	387.6	'	'
Long-term debt	398.5	397.6	'	'
Other long-term liabilities	81.1	101.2	'	'
Total liabilities	881	886.4	'	'
Koppers shareholders' equity	-409.3	-393.2	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	471.7	493.2	'	'
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Restricted cash	1.5	'	'	'
Accounts receivable, net	339.8	324.9	'	'
Inventories, net	0	0	'	'
Deferred tax assets	-1.5	-1.5	'	'
Other current assets	1.8	2.8	'	'
Total current assets	341.6	326.2	'	'
Equity investments	27.3	27.3	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	-12.4	-12.4	'	'
Other noncurrent assets	120.2	126.7	'	'
Total assets	476.7	467.8	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	14.7	17	'	'
Accrued liabilities	10.5	12.2	'	'
Total current liabilities	25.2	29.2	'	'
Long-term debt	0	0	'	'
Other long-term liabilities	2.4	2.4	'	'
Total liabilities	27.6	31.6	'	'
Koppers shareholders' equity	449.1	436.2	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	476.7	467.8	'	'
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	64.4	61.9	68.8	54.1
Restricted cash	0	'	'	'
Accounts receivable, net	92.9	86.8	'	'
Inventories, net	87.1	93.9	'	'
Deferred tax assets	0	0.2	'	'
Other current assets	26.8	30.1	'	'
Total current assets	271.2	272.9	'	'
Equity investments	4.2	3.8	'	'
Property, plant and equipment, net	64.3	55.4	'	'
Goodwill	33.6	35.8	'	'
Deferred tax assets	4.9	6.1	'	'
Other noncurrent assets	51.4	52.5	'	'
Total assets	429.6	426.5	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	53.2	60.6	'	'
Accrued liabilities	39.9	44.7	'	'
Total current liabilities	93.1	105.3	'	'
Long-term debt	57.9	64.4	'	'
Other long-term liabilities	29.5	31	'	'
Total liabilities	180.5	200.7	'	'
Koppers shareholders' equity	227.8	208.3	'	'
Noncontrolling interests	21.3	17.5	'	'
Total liabilities and equity	429.6	426.5	'	'
Consolidating Adjustments [Member] | Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Restricted cash	0	'	'	'
Accounts receivable, net	-357.4	-345.8	'	'
Inventories, net	-0.2	-0.3	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	-357.6	-346.1	'	'
Equity investments	-267.4	-251.1	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Other noncurrent assets	-160	-165.9	'	'
Total assets	-785	-763.1	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	-357.4	-345.9	'	'
Accrued liabilities	0	0	'	'
Total current liabilities	-357.4	-345.9	'	'
Long-term debt	-160	-165.9	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	-517.4	-511.8	'	'
Koppers shareholders' equity	-267.6	-251.3	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	($785)	($763.10)	'	'

Subsidiary_Guarantor_Informati7

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Statement of Cash Flows (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Subsidiary Guarantor Senior Notes [Line Items]	'	'
Cash provided by (used in) operating activities	$65.60	$54.50
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-29.4	-15.8
Net cash proceeds (payments) from divestitures and asset sales	2.4	0.7
Net cash provided by (used in) investing activities	-27	-15.1
Cash provided by (used in) financing activities:	'	'
Deferred financing costs	-1.2	-0.1
Dividends paid	-15.3	-14.5
Net cash provided by (used in) financing activities	-31.5	-27
Effect of exchange rates on cash	-1.4	2.4
Net increase (decrease) in cash and cash equivalents	5.7	14.8
Cash and cash equivalents at beginning of year	66.7	54.1
Cash and cash equivalents at end of period	72.4	68.9
Senior Notes [Member]	'	'
Subsidiary Guarantor Senior Notes [Line Items]	'	'
Cash provided by (used in) operating activities	65.6	54.5
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-29.4	-15.8
Net cash proceeds (payments) from divestitures and asset sales	2.4	0.7
Net cash provided by (used in) investing activities	-27	-15.1
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	'	-5
Deferred financing costs	-1.2	-0.1
Dividends paid	-15.3	-14.5
Other financing activities	2.3	'
Stock issued (repurchased)	-17.3	-7.4
Net cash provided by (used in) financing activities	-31.5	-27
Effect of exchange rates on cash	-1.4	2.4
Net increase (decrease) in cash and cash equivalents	5.7	14.8
Cash and cash equivalents at beginning of year	66.7	54.1
Cash and cash equivalents at end of period	72.4	68.9
Parent [Member] | Senior Notes [Member]	'	'
Subsidiary Guarantor Senior Notes [Line Items]	'	'
Cash provided by (used in) operating activities	32.6	21.8
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	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	'	0.1
Deferred financing costs	0	0
Dividends paid	-15.3	-14.5
Other financing activities	0	'
Stock issued (repurchased)	-17.3	-7.4
Net cash provided by (used in) financing activities	-32.6	-21.8
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 Guarantor Senior Notes [Line Items]	'	'
Cash provided by (used in) operating activities	39.7	32
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-13.3	-12.2
Net cash proceeds (payments) from divestitures and asset sales	1.4	0.3
Net cash provided by (used in) investing activities	-11.9	-11.9
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	'	-5
Deferred financing costs	-1.2	-0.1
Dividends paid	-23.5	-14.8
Other financing activities	0	'
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	-24.7	-19.9
Effect of exchange rates on cash	0.1	-0.1
Net increase (decrease) in cash and cash equivalents	3.2	0.1
Cash and cash equivalents at beginning of year	4.8	0
Cash and cash equivalents at end of period	8	0.1
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'
Subsidiary Guarantor Senior Notes [Line Items]	'	'
Cash provided by (used in) operating activities	0	0
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	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
Deferred financing costs	0	0
Dividends paid	0	0
Other financing activities	0	'
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	0	0
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
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'
Subsidiary Guarantor Senior Notes [Line Items]	'	'
Cash provided by (used in) operating activities	16.8	15.5
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-16.1	-3.6
Net cash proceeds (payments) from divestitures and asset sales	1	0.4
Net cash provided by (used in) investing activities	-15.1	-3.2
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	'	-0.1
Deferred financing costs	0	0
Dividends paid	0	0
Other financing activities	2.3	'
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	2.3	-0.1
Effect of exchange rates on cash	-1.5	2.5
Net increase (decrease) in cash and cash equivalents	2.5	14.7
Cash and cash equivalents at beginning of year	61.9	54.1
Cash and cash equivalents at end of period	64.4	68.8
Consolidating Adjustments [Member] | Senior Notes [Member]	'	'
Subsidiary Guarantor Senior Notes [Line Items]	'	'
Cash provided by (used in) operating activities	-23.5	-14.8
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	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
Deferred financing costs	0	0
Dividends paid	23.5	14.8
Other financing activities	0	'
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	23.5	14.8
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) (Shelf Registration [Member])	Sep. 30, 2013
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		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	$395.20	$387.90	$1,136.50	$1,180.10
Selling, general and administrative	18.3	19	52.2	55.1
Operating profit (loss)	39.1	30.8	92.5	100.7
Other income (expense)	1.3	0.6	2.8	1.7
Interest expense (income)	6.7	6.9	20.2	20.8
Income taxes	14.1	8.3	29.3	28.5
Income from continuing operations	19.6	16.2	45.8	53.1
Discontinued operations	-0.1	0	-0.1	-0.1
Noncontrolling interests	0.4	0.2	1.2	1
Net income attributable to Koppers	19.1	16	44.5	52
Comprehensive income attributable to Koppers	25.8	25	40.8	59.8
Shelf Registration [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	395.2	387.9	1,136.50	1,180.10
Cost of sales including depreciation and amortization	337.8	338.1	991.8	1,024.30
Selling, general and administrative	18.3	19	52.2	55.1
Operating profit (loss)	39.1	30.8	92.5	100.7
Other income (expense)	1.3	0.6	2.8	1.7
Interest expense (income)	6.7	6.9	20.2	20.8
Income taxes	14.1	8.3	29.3	28.5
Income from continuing operations	19.6	16.2	45.8	53.1
Discontinued operations	-0.1	0	-0.1	-0.1
Noncontrolling interests	0.4	0.2	1.2	1
Net income attributable to Koppers	19.1	16	44.5	52
Comprehensive income attributable to Koppers	25.8	25	40.8	59.8
Parent [Member] | Shelf Registration [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	0	0	0	0
Cost of sales including depreciation and amortization	0	'	0	0
Selling, general and administrative	0.5	0.4	1.5	1.3
Operating profit (loss)	-0.5	-0.4	-1.5	-1.3
Other income (expense)	19.4	16.3	45.4	52.9
Interest expense (income)	0	0.1	0	0.1
Income taxes	-0.2	-0.2	-0.6	-0.5
Income from continuing operations	19.1	16	44.5	52
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	19.1	16	44.5	52
Comprehensive income attributable to Koppers	25.8	25	40.8	59.8
Koppers Inc. [Member] | Shelf Registration [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	230.1	238.2	660.3	689.1
Cost of sales including depreciation and amortization	197.5	211	580.6	601.9
Selling, general and administrative	10.8	11.6	29.7	33
Operating profit (loss)	21.8	15.6	50	54.2
Other income (expense)	0.4	0.4	1.3	0.4
Interest expense (income)	6.7	6.9	20.2	20.7
Income taxes	10.2	7	21.3	20.5
Income from continuing operations	5.3	2.1	9.8	13.4
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	5.3	2.1	9.8	13.4
Comprehensive income attributable to Koppers	6.4	3.3	13	16.9
Domestic Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	11.9	15.1	48.5	73
Cost of sales including depreciation and amortization	7.2	9.3	34.3	49.2
Selling, general and administrative	0.1	0.4	0.7	1.6
Operating profit (loss)	4.6	5.4	13.5	22.2
Other income (expense)	1.1	0.3	6.3	0.8
Interest expense (income)	0.2	0	0.1	0
Income taxes	0	0.1	0.2	0.3
Income from continuing operations	5.5	5.6	19.5	22.7
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	5.5	5.6	19.5	22.7
Comprehensive income attributable to Koppers	5.7	8.1	12.9	24.9
Foreign Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	120.7	118.6	348.6	355.4
Cost of sales including depreciation and amortization	103.6	102.3	305.7	309.6
Selling, general and administrative	5.5	5.6	16.8	16.7
Operating profit (loss)	11.6	10.7	26.1	29.1
Other income (expense)	0.7	0.1	0.8	0.1
Interest expense (income)	0.6	1	2.5	3
Income taxes	3.8	1.4	7.4	7.5
Income from continuing operations	7.9	8.4	17	18.7
Discontinued operations	-0.1	0	-0.1	-0.1
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	7.8	8.4	16.9	18.6
Comprehensive income attributable to Koppers	13.2	14.3	14.4	21.4
Non-Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	43.4	29.2	123.9	111.3
Cost of sales including depreciation and amortization	40.5	27.4	116.1	103.3
Selling, general and administrative	1.4	1	3.5	2.5
Operating profit (loss)	1.5	0.8	4.3	5.5
Other income (expense)	0.1	-0.2	0.7	0.4
Interest expense (income)	0.2	0.2	0.6	0.9
Income taxes	0.3	0	1	0.7
Income from continuing operations	1.1	0.4	3.4	4.3
Discontinued operations	0	0	0	0
Noncontrolling interests	0.4	0.2	1.2	1
Net income attributable to Koppers	0.7	0.2	2.2	3.3
Comprehensive income attributable to Koppers	1.3	0.4	2.8	3.3
Consolidating Adjustments [Member] | Shelf Registration [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	-10.9	-13.2	-44.8	-48.7
Cost of sales including depreciation and amortization	-11	-11.9	-44.9	-39.7
Selling, general and administrative	0	0	0	0
Operating profit (loss)	0.1	-1.3	0.1	-9
Other income (expense)	-20.4	-16.3	-51.7	-52.9
Interest expense (income)	-1	-1.3	-3.2	-3.9
Income taxes	0	0	0	0
Income from continuing operations	-19.3	-16.3	-48.4	-58
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	-19.3	-16.3	-48.4	-58
Comprehensive income attributable to Koppers	($26.60)	($26.10)	($43.10)	($66.50)

Recovered_Sheet1

Subsidiary Guarantor Information for Shelf Registration - Condensed Consolidating Balance Sheet (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Assets	'	'	'	'
Cash and cash equivalents	$72.40	$66.70	$68.90	$54.10
Accounts receivable, net	182.1	162.7	'	'
Inventories, net	166.4	195.8	'	'
Deferred tax assets	14.7	15.1	'	'
Other current assets	25.6	31.4	'	'
Total current assets	472.2	481.2	'	'
Equity investments	6.2	5.8	'	'
Property, plant and equipment, net	169.4	161.1	'	'
Goodwill	73.4	75.6	'	'
Deferred tax assets	12.6	27.2	'	'
Other noncurrent assets	27.3	29.1	'	'
Total assets	761.1	780	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	94.9	103.5	'	'
Accrued liabilities	66.3	72.1	'	'
Total current liabilities	167	181.2	'	'
Long-term debt	296.4	296.1	'	'
Total liabilities	576.4	611.9	'	'
Koppers shareholders' equity	163.4	150.6	'	'
Noncontrolling interests	21.3	17.5	'	'
Total liabilities and equity	761.1	780	'	'
Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	72.4	66.7	68.9	54.1
Restricted cash	1.5	'	'	'
Accounts receivable, net	182.1	162.7	'	'
Inventories, net	166.4	195.8	'	'
Deferred tax assets	14.7	15.1	'	'
Other current assets	35.1	40.9	'	'
Total current assets	472.2	481.2	'	'
Equity investments	6.2	5.8	'	'
Property, plant and equipment, net	169.4	161.1	'	'
Goodwill	73.4	75.6	'	'
Deferred tax assets	12.6	27.2	'	'
Other noncurrent assets	27.3	29.1	'	'
Total assets	761.1	780	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	94.9	103.5	'	'
Accrued liabilities	72.1	77.7	'	'
Total current liabilities	167	181.2	'	'
Long-term debt	296.4	296.1	'	'
Other long-term liabilities	113	134.6	'	'
Total liabilities	576.4	611.9	'	'
Koppers shareholders' equity	163.4	150.6	'	'
Noncontrolling interests	21.3	17.5	'	'
Total liabilities and equity	761.1	780	'	'
Parent [Member] | Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Restricted cash	0	'	'	'
Accounts receivable, net	6.7	6.9	'	'
Inventories, net	0	0	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	6.7	6.9	'	'
Equity investments	161.3	148.7	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Other noncurrent assets	0.1	0	'	'
Total assets	168.1	155.6	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0.1	0.1	'	'
Accrued liabilities	4.6	4.9	'	'
Total current liabilities	4.7	5	'	'
Long-term debt	0	0	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	4.7	5	'	'
Koppers shareholders' equity	163.4	150.6	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	168.1	155.6	'	'
Koppers Inc. [Member] | Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	8	4.8	0.1	0
Restricted cash	0	'	'	'
Accounts receivable, net	100.1	89.9	'	'
Inventories, net	79.5	102.2	'	'
Deferred tax assets	16.2	16.4	'	'
Other current assets	6.5	8	'	'
Total current assets	210.3	221.3	'	'
Equity investments	80.8	77.1	'	'
Property, plant and equipment, net	105.1	105.7	'	'
Goodwill	39.8	39.8	'	'
Deferred tax assets	20.1	33.5	'	'
Other noncurrent assets	15.6	15.8	'	'
Total assets	471.7	493.2	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	384.3	371.7	'	'
Accrued liabilities	17.1	15.9	'	'
Total current liabilities	401.4	387.6	'	'
Long-term debt	398.5	397.6	'	'
Other long-term liabilities	81.1	101.2	'	'
Total liabilities	881	886.4	'	'
Koppers shareholders' equity	-409.3	-393.2	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	471.7	493.2	'	'
Domestic Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Restricted cash	1.5	'	'	'
Accounts receivable, net	339.8	324.9	'	'
Inventories, net	0	0	'	'
Deferred tax assets	-1.5	-1.5	'	'
Other current assets	1.8	2.8	'	'
Total current assets	341.6	326.2	'	'
Equity investments	27.3	27.3	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	-12.4	-12.4	'	'
Other noncurrent assets	120.2	126.7	'	'
Total assets	476.7	467.8	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	14.7	17	'	'
Accrued liabilities	10.5	12.2	'	'
Total current liabilities	25.2	29.2	'	'
Long-term debt	0	0	'	'
Other long-term liabilities	2.4	2.4	'	'
Total liabilities	27.6	31.6	'	'
Koppers shareholders' equity	449.1	436.2	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	476.7	467.8	'	'
Foreign Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	48.3	40.7	66.2	45.1
Restricted cash	0	'	'	'
Accounts receivable, net	58.7	65.9	'	'
Inventories, net	79.9	86.7	'	'
Deferred tax assets	0	0	'	'
Other current assets	10.6	17.6	'	'
Total current assets	197.5	210.9	'	'
Equity investments	36.4	30.2	'	'
Property, plant and equipment, net	41	40.7	'	'
Goodwill	32.3	34.4	'	'
Deferred tax assets	6.5	7.6	'	'
Other noncurrent assets	10.4	12.1	'	'
Total assets	324.1	335.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	32.9	42.2	'	'
Accrued liabilities	30.3	35.7	'	'
Total current liabilities	63.2	77.9	'	'
Long-term debt	57.9	64.4	'	'
Other long-term liabilities	22.7	24.5	'	'
Total liabilities	143.8	166.8	'	'
Koppers shareholders' equity	180.3	169.1	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	324.1	335.9	'	'
Non-Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	16.1	21.2	2.6	9
Restricted cash	0	'	'	'
Accounts receivable, net	34.2	21.2	'	'
Inventories, net	7.2	7.2	'	'
Deferred tax assets	0	0.2	'	'
Other current assets	16.2	12.5	'	'
Total current assets	73.7	62.3	'	'
Equity investments	4.2	3.8	'	'
Property, plant and equipment, net	23.3	14.7	'	'
Goodwill	1.3	1.4	'	'
Deferred tax assets	-1.6	-1.5	'	'
Other noncurrent assets	41.1	40.3	'	'
Total assets	142	121	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	20.3	18.6	'	'
Accrued liabilities	9.6	9	'	'
Total current liabilities	29.9	27.6	'	'
Long-term debt	0	0	'	'
Other long-term liabilities	6.8	6.5	'	'
Total liabilities	36.7	34.1	'	'
Koppers shareholders' equity	84	69.4	'	'
Noncontrolling interests	21.3	17.5	'	'
Total liabilities and equity	142	121	'	'
Consolidating Adjustments [Member] | Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Restricted cash	0	'	'	'
Accounts receivable, net	-357.4	-346.1	'	'
Inventories, net	-0.2	-0.3	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	-357.6	-346.4	'	'
Equity investments	-303.8	-281.3	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Other noncurrent assets	-160.1	-165.8	'	'
Total assets	-821.5	-793.5	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	-357.4	-346.1	'	'
Accrued liabilities	0	0	'	'
Total current liabilities	-357.4	-346.1	'	'
Long-term debt	-160	-165.9	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	-517.4	-512	'	'
Koppers shareholders' equity	-304.1	-281.5	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	($821.50)	($793.50)	'	'

Recovered_Sheet2

Subsidiary Guarantor Information for Shelf Registration - Condensed Consolidating Statement of Cash Flows (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	$65.60	$54.50
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-29.4	-15.8
Net cash proceeds (payments) from divestitures and asset sales	2.4	0.7
Net cash provided by (used in) investing activities	-27	-15.1
Cash provided by (used in) financing activities:	'	'
Deferred financing costs	-1.2	-0.1
Dividends paid	-15.3	-14.5
Net cash provided by (used in) financing activities	-31.5	-27
Effect of exchange rates on cash	-1.4	2.4
Net increase (decrease) in cash and cash equivalents	5.7	14.8
Cash and cash equivalents at beginning of year	66.7	54.1
Cash and cash equivalents at end of period	72.4	68.9
Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	65.6	54.5
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-29.4	-15.8
Net cash proceeds (payments) from divestitures and asset sales	2.4	0.7
Net cash provided by (used in) investing activities	-27	-15.1
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	'	-5
Deferred financing costs	-1.2	-0.1
Dividends paid	-15.3	-14.5
Other financing activities	2.3	'
Stock issued (repurchased)	-17.3	-7.4
Net cash provided by (used in) financing activities	-31.5	-27
Effect of exchange rates on cash	-1.4	2.4
Net increase (decrease) in cash and cash equivalents	5.7	14.8
Cash and cash equivalents at beginning of year	66.7	54.1
Cash and cash equivalents at end of period	72.4	68.9
Parent [Member] | Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	32.6	21.8
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	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	'	0.1
Deferred financing costs	0	0
Dividends paid	-15.3	-14.5
Other financing activities	0	'
Stock issued (repurchased)	-17.3	-7.4
Net cash provided by (used in) financing activities	-32.6	-21.8
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] | Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	39.7	32
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-13.3	-12.2
Net cash proceeds (payments) from divestitures and asset sales	1.4	0.3
Net cash provided by (used in) investing activities	-11.9	-11.9
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	'	-5
Deferred financing costs	-1.2	-0.1
Dividends paid	-23.5	-14.8
Other financing activities	0	'
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	-24.7	-19.9
Effect of exchange rates on cash	0.1	-0.1
Net increase (decrease) in cash and cash equivalents	3.2	0.1
Cash and cash equivalents at beginning of year	4.8	0
Cash and cash equivalents at end of period	8	0.1
Domestic Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	0	0
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	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
Deferred financing costs	0	0
Dividends paid	0	0
Other financing activities	0	'
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	0	0
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
Foreign Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	14.9	21.5
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-6.6	-3.2
Net cash proceeds (payments) from divestitures and asset sales	1.1	0.3
Net cash provided by (used in) investing activities	-5.5	-2.9
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	'	0
Deferred financing costs	0	0
Dividends paid	0	0
Other financing activities	0	'
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	0	0
Effect of exchange rates on cash	-1.8	2.5
Net increase (decrease) in cash and cash equivalents	7.6	21.1
Cash and cash equivalents at beginning of year	40.7	45.1
Cash and cash equivalents at end of period	48.3	66.2
Non-Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	1.9	-6
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-9.5	-0.4
Net cash proceeds (payments) from divestitures and asset sales	-0.1	0.1
Net cash provided by (used in) investing activities	-9.6	-0.3
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	'	-0.1
Deferred financing costs	0	0
Dividends paid	0	0
Other financing activities	2.3	'
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	2.3	-0.1
Effect of exchange rates on cash	0.3	0
Net increase (decrease) in cash and cash equivalents	-5.1	-6.4
Cash and cash equivalents at beginning of year	21.2	9
Cash and cash equivalents at end of period	16.1	2.6
Consolidating Adjustments [Member] | Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	-23.5	-14.8
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	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
Deferred financing costs	0	0
Dividends paid	23.5	14.8
Other financing activities	0	'
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	23.5	14.8
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 $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Nov. 30, 2011
Related Party Transactions [Abstract]	'	'	'
Loan to related party	$9.50	$9.50	$11.70
Ownership percentage	30.00%	'	30.00%
Repayment of loan	$2.20	'	'
Loan repayable date	'November 2013	'	'
Loan repayment extended period	'1 year	'	'