Koppers (KOP) 10-Q 10 Nov 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014	Oct. 31, 2014
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Trading Symbol	'KOP	'
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	'	20,495,011

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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]	'	'	'	'
Net sales	$440.10	$395.20	$1,128.30	$1,136.50
Cost of sales (excluding items below)	377	330.6	974	970
Depreciation and amortization	11.2	7.2	29.8	21.8
Impairment and restructuring charges	2.6	0	18.1	0
Selling, general and administrative expenses	32	18.3	75.3	52.2
Operating profit (loss)	17.3	39.1	31.1	92.5
Other (loss) income	-0.2	1.3	-0.3	2.8
Interest expense	11.9	6.7	25.3	20.2
Income before income taxes	5.2	33.7	5.5	75.1
Income taxes	9.5	14.1	9.1	29.3
(Loss) income from continuing operations	-4.3	19.6	-3.6	45.8
Income (loss) from discontinued operations, net of tax benefit of $0.0, $0.1, $0.0 and $0.1	0.1	-0.1	0	-0.1
Net (loss) income	-4.2	19.5	-3.6	45.7
Net (loss) income attributable to noncontrolling interests	-1.5	0.4	-4.7	1.2
Net (loss) income attributable to Koppers	-2.7	19.1	1.1	44.5
Basic -	'	'	'	'
Continuing operations	($0.14)	$0.93	$0.05	$2.16
Discontinued operations	$0	$0	$0	$0
(Loss) Earnings per basic common share	($0.14)	$0.93	$0.05	$2.16
Diluted -	'	'	'	'
Continuing operations	($0.14)	$0.92	$0.05	$2.13
Discontinued operations	$0	$0	$0	$0
(Loss) Earnings per diluted common share	($0.14)	$0.92	$0.05	$2.13
Comprehensive (loss) income	-19.9	26.6	-14.1	42.3
Comprehensive (loss) income attributable to noncontrolling interests	-1.3	0.8	-4.9	1.5
Comprehensive (loss) income attributable to Koppers	($18.60)	$25.80	($9.20)	$40.80
Weighted average shares outstanding (in thousands):	'	'	'	'
Basic	20,495	20,577	20,452	20,657
Diluted	20,603	20,801	20,593	20,887
Dividends declared per common share	$0.25	$0.25	$0.75	$0.75

Condensed_Consolidated_Stateme1

Condensed Consolidated Statement of Comprehensive Income (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]	'	'	'	'
Loss from discontinued operations, tax benefit	$0	$0.10	$0	$0.10

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheet (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Assets	'	'
Cash and cash equivalents	$75.10	$82.20
Accounts receivable, net of allowance of $6.5 and $3.6	229.5	157.9
Income tax receivable	6.4	9
Inventories, net	227.7	168.8
Deferred tax assets	20.2	10
Loan to related party	9.5	9.5
Other current assets	39.6	35.7
Total current assets	608	473.1
Equity in non-consolidated investments	5.7	6.6
Property, plant and equipment, net	286.8	197
Goodwill	238	72.7
Intangible assets, net	180.1	12.2
Deferred tax assets	10.3	9.3
Other assets	25	14
Total assets	1,353.90	784.9
Liabilities	'	'
Accounts payable	122.4	107.6
Accrued liabilities	102.6	82.4
Dividends payable	5.1	5.1
Current maturities of long-term debt	30	0
Total current liabilities	260.1	195.1
Long-term debt	837.5	303.1
Accrued postretirement benefits	27.7	41.6
Deferred tax liabilities	20.6	14.7
Other long-term liabilities	43	40.6
Total liabilities	1,188.90	595.1
Commitments and contingent liabilities (Note 18)	'	'
Equity	'	'
Senior Convertible Preferred Stock, $0.01 par value per share; 10,000,000 shares authorized; no shares issued	0	0
Common Stock, $0.01 par value per share; 40,000,000 shares authorized; 21,938,260 and 21,722,492 shares issued	0.2	0.2
Additional paid-in capital	164.5	158.9
Retained earnings	56.7	71.3
Accumulated other comprehensive loss	-20.4	-10.2
Treasury stock, at cost, 1,443,248 and 1,390,494 shares	-52.4	-50.4
Total Koppers shareholders' equity	148.6	169.8
Noncontrolling interests	16.4	20
Total equity	165	189.8
Total liabilities and equity	$1,353.90	$784.90

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheet (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Accounts receivable, allowance	$6.50	$3.60
Senior Convertible Preferred Stock, par value	$0.01	$0.01
Senior Convertible Preferred Stock, shares authorized	10,000,000	10,000,000
Senior Convertible Preferred Stock, shares issued	0	0
Common stock, par value	$0.01	$0.01
Common Stock, shares authorized	40,000,000	40,000,000
Common Stock, shares issued	21,938,260	21,722,492
Treasury stock, shares	1,443,248	1,390,494

Condensed_Consolidated_Stateme2

Condensed Consolidated Statement of Cash Flows (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Cash provided by (used in) operating activities:	'	'
Net (loss) income	($3.60)	$45.70
Adjustments to reconcile net cash provided by operating activities:	'	'
Depreciation and amortization	29.8	21.8
Impairment charges	4.7	0
Deferred income taxes	-3.2	11.1
Equity loss (income), net of dividends received	0.9	-0.4
Gain on sale of assets	0	-1.9
Change in other liabilities	-10.9	-14.2
Non-cash interest expense	3.4	1.2
Stock-based compensation	4.6	4.7
Other	-1.5	0.6
(Increase) decrease in working capital:	'	'
Accounts receivable	-15.6	-17.9
Inventories	4.9	25.5
Accounts payable	-6.1	-8
Accrued liabilities and other working capital	3.4	-2.6
Net cash provided by (used in) operating activities	10.8	65.6
Cash provided by (used in) investing activities:	'	'
Capital expenditures	-59	-29.4
Acquisitions, (net of cash acquired)	-496.5	0
Net cash proceeds from divestitures and asset sales	0.1	2.4
Net cash provided by (used in) investing activities	-555.4	-27
Cash provided by (used in) financing activities:	'	'
Borrowings of revolving credit	520.7	97.9
Repayments of revolving credit	-305.8	-97.9
Borrowings of long-term debt	348.9	0
Issuances of Common Stock	0.7	0.2
Proceeds from issuance of noncontrolling interest	1.4	2.3
Repurchases of Common Stock	-2	-17.5
Payment of deferred financing costs	-11.1	-1.2
Dividends paid	-15.2	-15.3
Net cash provided by (used in) financing activities	537.6	-31.5
Effect of exchange rate changes on cash	-0.1	-1.4
Net (decrease) increase in cash and cash equivalents	-7.1	5.7
Cash and cash equivalents at beginning of period	82.2	66.7
Cash and cash equivalents at end of period	$75.10	$72.40

Basis_of_Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Basis of Presentation	'
	1. Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements and related disclosures have been prepared in accordance with accounting principles generally accepted in the United States applicable to interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation of Koppers Holdings Inc.’s and its subsidiaries’ (“Koppers”, “Koppers Holdings” or the “Company”) financial position and interim results as of and for the periods presented have been included. All such adjustments are of a normal recurring nature unless disclosed otherwise. Because the Company’s business is seasonal, results for interim periods are not necessarily indicative of those that may be expected for a full year. The Condensed Consolidated Balance Sheet for December 31, 2013 has been summarized from the audited balance sheet contained in the Annual Report on Form 10-K for the year ended December 31, 2013.
	The financial information included herein should be read in conjunction with the Company’s audited consolidated financial statements and related notes included in its Annual Report on Form 10-K for the year ended December 31, 2013.

Dividends

Dividends	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Dividends	'
	2. Dividends
	On November 5, 2014, the Company’s board of directors declared a quarterly dividend of 25 cents per common share, payable on January 5, 2015 to shareholders of record as of November 17, 2014.

Plant_Closures_and_Discontinue

Plant Closures and Discontinued Operations	9 Months Ended
	Sep. 30, 2014
Discontinued Operations and Disposal Groups [Abstract]	'
Plant Closures and Discontinued Operations	'
	3. Plant Closures and Discontinued Operations
	On January 22, 2014, the Company announced its decision to discontinue coal tar distillation activities at its facility located in Uithoorn, the Netherlands. The decision was made as a result of a detailed analysis of its overall European manufacturing asset footprint in light of deteriorating market conditions in Europe and a variety of other factors, including regulatory requirements for significant capital expenditures at the facility. The Company has discontinued distillation activities and expects to complete closure at the site by the end of 2015. For the nine months ended September 30, 2014, the Company recorded closure costs of $13.1 million for severance and site demolition liabilities. In the fourth quarter of 2013, the Company recorded an asset impairment charge of $6.9 million related to the facility. The facility is part of the Carbon Materials and Chemicals segment.
	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 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			Site			Other			Total
		employee benefits			remediation			demolition
	(Dollars in millions)
	Reserve at December 31, 2012	$	0.2		$	6.7		$	6.3		$	0.1		$	13.3
	Reversal of accrued charges		(0.1	)		0			(0.3	)		0			(0.4	)
	Cash paid		0			(0.1	)		(2.0	)		(0.1	)		(2.2	)
	Currency translation		0			(1.0	)		(0.7	)		0			(1.7	)
	Reserve at December 31, 2013	$	0.1		$	5.6		$	3.3		$	0		$	9
	Accrual		10			0			3.1			0			13.1
	Cash paid		(9.3	)		0			(0.2	)		0			(9.5	)
	Currency translation		(0.2	)		(0.1	)		(0.1	)		0			(0.4	)
	Reserve at September 30, 2014	$	0.6		$	5.5		$	6.1		$	0		$	12.2

Business_Acquisitions

Business Acquisitions	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Business Acquisitions	'
	4. Business Acquisitions
	Koppers Ashcroft – On January 20, 2014, the Company acquired the crosstie treating business and related manufacturing facility of Tolko Industries Ltd. located in Ashcroft, British Columbia, Canada. The purchase price was $29.8 million, subject to post-closing adjustments, and was funded primarily by available cash. The preliminary allocation of purchase price to acquired assets primarily consisted of inventory totaling $16.0 million, plant and equipment totaling $3.6 million, intangible assets consisting primarily of customer relationships totaling $7.4 million and Canadian tax deductible goodwill of $1.8 million. The goodwill is allocated to the Railroad and Utility Products and Services segment and the customer contracts will be amortized over a period of 12 years.
	Osmose Entities – On August 15, 2014, pursuant to the terms and conditions of a stock purchase agreement, Koppers Inc. acquired Osmose, Inc. and Osmose Railroad Services, Inc. (together, the “Osmose Entities”) from Osmose Holdings, Inc. The aggregate cash purchase price was $494.1 million, net of estimated cash acquired of $27.2 million, and included estimated net working capital adjustments and is subject to certain post-closing adjustments, including but not limited to, final net working capital adjustments. The cash purchase price was funded by a new credit agreement with a consortium of banks which provides for a $500 million revolving credit facility and a $300 million term loan.
	Subsequent to the acquisition, Osmose, Inc. was renamed Koppers Performance Chemicals Inc. and Osmose Railroad Services, Inc. was renamed Koppers Railroad Structures Inc. Koppers Performance Chemicals Inc.’s wood preservation business develops, manufactures and sells wood preservation chemicals and wood treatment technologies for infrastructure, residential and commercial construction, and agricultural markets. The wood preservation business has operations and sales in North America, South America, Europe, and Australasia. Substantially all of the businesses of Koppers Performance Chemicals Inc. are reported as a new segment, Performance Chemicals. Koppers Railroad Structures Inc. is a provider of railroad infrastructure services, including bridge inspection, engineering, maintenance and repair, and construction services for the Class I and shortline railroads in North America. Koppers Railroad Structures Inc. and one wood treating company are reported as part of the Railroad and Utility Products and Services segment.
	The Osmose Entities had revenues of $391.5 million and net income from continuing operations of $19.3 million for the year ended December 31, 2013. Revenue from the Osmose Entities included in our results for the third quarter of 2014 totaled $53.4 million.
	The Company has not completed detailed valuation analyses to determine the fair values of Osmose Entities’ assets and liabilities. Accordingly, the unaudited condensed consolidated financial information includes a preliminary fair value determination based on assumptions and estimates that, while considered reasonable under the circumstances, are subject to changes, which may be material. In addition, Koppers has not yet completed the due diligence necessary to identify all of the adjustments required to conform Osmose Entities’ accounting policies to the Company’s or to identify other items that could significantly impact the fair value determination or the assumptions and adjustments made in the preparation of this unaudited condensed consolidated financial information.
	Upon completion of detailed valuation analyses, there may be additional increases or decreases to the recorded book values of the acquired assets and liabilities, including but not limited to inventories, brands, trademarks, customer relationships and other intangible assets, and property, plant and equipment that could give rise to future amounts of depreciation and amortization expense and changes in related deferred taxes that are not reflected in the information contained in this unaudited condensed consolidated information. Accordingly, once the necessary valuation analyses have been performed and the final fair value determination has been completed, actual results may differ materially from the information presented in this unaudited condensed consolidated financial information.
	The following table summarizes the Company’s preliminary fair value estimates for the Osmose entities as of September 30, 2014:
	(Dollars in millions)	Initial
		Allocation
	Cash and cash equivalents	$	27.2
	Accounts receivable, net		60
	Inventories, net		51.9
	Other current assets		9.5
	Property, plant and equipment		59.6
	Goodwill		164.8
	Intangible assets		164.2
	Other assets		4
	Total assets acquired		541.2
	Accounts payable		21.2
	Accrued liabilities		17.4
	Other liabilities		8.5
	Total liabilities assumed		47.1
	Net assets acquired	$	494.1
	Goodwill is calculated as the excess of the consideration transferred over the assets acquired and represents the estimated future economic benefits arising from the other assets acquired that could not be individually identified and separately recognized. Goodwill of $158.0 million and $6.8 million has been allocated, on a preliminary basis, to the Performance Chemicals segment and the Railroad and Utility Products and Services segment, respectively. The Company expects that a significant portion of the goodwill recognized will be deductible for tax purposes, but this determination is dependent upon the finalization of the purchase price allocation process.
	The following unaudited pro forma information presents a summary of the Company’s revenues and net income from continuing operations as if the acquisition occurred on January 1, 2013 (the first day of the most recently completed fiscal year). The unaudited pro forma information is not necessarily indicative of operating results that would have been achieved had the acquisition been completed as of January 1, 2013 and does not intend to project the future financial results of the Company after the acquisition of the Osmose Entities. The unaudited pro forma information is based on certain assumptions, which management believes are reasonable, and do not reflect the cost of any integration activities or the benefits from the acquisition and synergies that may be derived from any integration activities.
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	(Dollars in millions)
	Revenue	$	500.1	$	498.4	$	1,392.90	$	1,433.00
	Income from continuing operations attributable to Koppers		3.4		23.2		16.4		45.1
	Pro forma adjustments reflected in the unaudited pro forma information are based on items that are directly attributable to the acquisition of the Osmose Entities and related financing that are factually supportable and are expected to have a continuing impact on Koppers. These adjustments include, but are not limited to, depreciation and amortization related to fair value adjustments to property, plant and equipment and intangible assets, interest expense on acquisition-related debt, removal of acquisition related transaction expenses, elimination of intercompany sales and related income tax effects of the pro forma adjustments.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	5. Fair Value Measurements
	Carrying amounts and the related estimated fair values of the Company’s financial instruments as of September 30, 2014 and December 31, 2013 are as follows:
			September 30, 2014				December 31, 2013
			Fair Value		Carrying		Fair Value		Carrying
					Value				Value
	(Dollars in millions)
	Financial assets:
	Cash and cash equivalents, including restricted cash		$	75.1	$	75.1	$	82.2	$	82.2
	Investments and other assets(a)			1.4		1.4		1.4		1.4
	Financial liabilities:
	Long-term debt (including current portion)		$	883.7	$	867.5	$	331.2	$	303.1
	(a)	Excludes equity method investments.
	Cash and cash equivalents – The carrying amount approximates fair value because of the short maturity of those instruments.
	Investments and other assets – Represents the broker-quoted cash surrender value on universal life insurance policies. This asset is classified as Level 2 in the valuation hierarchy and is measured from values received from financial institutions.
	Debt – The fair value of the Company’s long-term debt is estimated based on the market prices for the same or similar issues or on the current rates offered to the Company for debt of the same remaining maturities (Level 2). The fair values of the revolving credit facility 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, 2014
Equity [Abstract]	'
Comprehensive Income and Equity	'
	6. Comprehensive Income and Equity
	Total comprehensive income for the three and nine months ended September 30, 2014 and 2013 is summarized in the table below:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
	(Dollars in millions)
	Net (loss) income	$	(4.2	)	$	19.5		$	(3.6	)	$	45.7
	Other comprehensive (loss) income:
	Change in currency translation adjustment		(10.6	)		5.6			(9.8	)		(0.4	)
	Change in foreign currency transactions of long-term subsidiary investments		(3.8	)		0.3			(0.5	)		(6.6	)
	Change in derivative financial instrument net loss, net of tax benefit of $(0.8), $0.0, $(0.8) and $0.0		(1.9	)		0			(1.9	)		0
	Change in unrecognized pension net loss, net of tax expense of $0.2, $0.8, $0.7 and $2.3		0.6			1.2			1.8			3.5
	Change in unrecognized prior service cost, net of tax expense of $0.0, $0.0, $0.0 and $0.0		0			0			(0.1	)		0.1
	Total comprehensive (loss) income		(19.9	)		26.6			(14.1	)		42.3
	Less: comprehensive (loss) income attributable to noncontrolling interests		(1.3	)		0.8			(4.9	)		1.5
	Comprehensive (loss) income attributable to Koppers	$	(18.6	)	$	25.8		$	(9.2	)	$	40.8
	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 13 – Pensions and Postretirement Benefit Plans.
	The following tables present the change in equity for the nine months ended September 30, 2014 and 2013, respectively:
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity
	Balance at December 31, 2013	$	169.8		$	20		$	189.8
	Net income (loss)		1.1			(4.7	)		(3.6	)
	Issuance of common stock		0.7			0			0.7
	Employee stock plans		4.9			0			4.9
	Other comprehensive income (loss)		(10.3	)		(0.2	)		(10.5	)
	Dividends		(15.6	)		0			(15.6	)
	Investment in noncontrolling interests		0			1.3			1.3
	Repurchases of common stock		(2.0	)		0			(2.0	)
	Balance at September 30, 2014	$	148.6		$	16.4		$	165
	(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 (loss) income		(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

Earnings_per_Common_Share

Earnings per Common Share	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Earnings per Common Share	'
	7. Earnings per Common Share
	The computation of basic earnings per common share for the periods presented is based upon the weighted average number of common shares outstanding during the periods. The computation of diluted earnings per common share includes the effect of non-vested nonqualified stock options and restricted stock units assuming such options and stock units were outstanding common shares at the beginning of the period. The effect of antidilutive securities is excluded from the computation of diluted earnings per common share.
	The following table sets forth the computation of basic and diluted earnings per common share:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014		2013
	(Dollars in millions, except share amounts, in thousands, and per share amounts)
	Net (loss) income attributable to Koppers	$	(2.7	)	$	19.1		$	1.1	$	44.5
	Less: income (loss) from discontinued operations		0.1			(0.1	)		0		(0.1	)
	(Loss) Income from continuing operations attributable to Koppers	$	(2.8	)	$	19.2		$	1.1	$	44.6
	Weighted average common shares outstanding:
	Basic		20,495			20,577			20,452		20,657
	Effect of dilutive securities		108			224			141		230
	Diluted		20,603			20,801			20,593		20,887
	(Loss) earnings per common share – continuing operations:
	Basic (loss) earnings per common share	$	(0.14	)	$	0.93		$	0.05	$	2.16
	Diluted (loss) earnings per common share		(0.14	)		0.92			0.05		2.13
	Other data:
	Antidilutive securities excluded from computation of diluted earnings per common share		265			254			260		236

Stockbased_Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Stock-based Compensation	'
	8. Stock-based Compensation
	The amended and restated 2005 Long-Term Incentive Plan (the “LTIP”) provides for the grant to eligible persons of stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance awards, dividend equivalents and other stock-based awards, which are collectively referred to as the awards.
	Under the LTIP, the board of directors granted restricted stock units and performance stock units to certain employee participants (collectively, the “stock units”). The restricted stock units vest on the third anniversary of the grant date or ratably over three years, assuming continued employment by the participant. Performance stock units granted in 2011 have a two-year performance objective. Performance stock units granted after 2011 have three-year performance objectives. Regardless of whether the measurement period for the applicable performance objective is two or three years, all performance stock units have a three-year period for vesting (if the applicable performance objective is obtained). The applicable performance objective is based upon a multi-year cumulative value creation calculation commencing on the first day of each grant year. The number of performance stock units granted represents the target award and participants have the ability to earn between zero and 150 percent of the target award based upon actual performance. If minimum performance criteria are not achieved, no performance stock units will vest.
	Dividends declared on the Company’s common stock during the restriction period of the stock units are credited at equivalent value as additional stock units and become payable as additional common shares upon vesting. In the event of termination of employment, other than retirement, death or disability, any non-vested stock units are forfeited, including additional stock units credited from dividends. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the stock units over the service period will result for most participants. There are special vesting provisions for the stock units related to a change in control.
	Restricted stock units that vest immediately or have one-year vesting periods are also issued under the LTIP to members of the board of directors in connection with annual director compensation and, from time to time, are issued to members of management in connection with employee compensation.
	Compensation expense for non-vested stock units is recorded over the vesting period based on the fair value at the date of grant. The fair value of stock units is the market price of the underlying common stock on the date of grant.
	The following table shows a summary of the performance stock units as of September 30, 2014:
	Performance Period	Minimum			Target			Maximum
		Shares			Shares			Shares
	2012 – 2014		0			87,059			130,559
	2013 – 2015		0			85,207			127,811
	2014 – 2016		0			102,149			153,224
	The following table shows a summary of the status and activity of non-vested stock awards for the nine months ended September 30, 2014:
		Restricted			Performance			Total			Weighted Average
		Stock Units			Stock Units			Stock Units			Grant Date Fair
											Value per Unit
	Non-vested at December 31, 2013		148,836			319,984			468,820		$	40.3
	Granted		95,067			108,506			203,573		$	37.9
	Credited from dividends		3,813			8,425			12,238		$	38.52
	Vested		(57,102	)		(132,317	)		(189,419	)	$	40.18
	Forfeited		(12,695	)		(24,218	)		(36,913	)	$	39.51
	Non-vested at September 30, 2014		177,919			280,380			458,299		$	39.3
	Stock options to most executive officers vest and become exercisable upon the completion of a three-year service period commencing on the grant date. The stock options have a term of 10 years. In the event of termination of employment, other than retirement, death or disability, any non-vested options are forfeited for most participants. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the options over the service period will result for most participants. There are special vesting provisions for the stock options related to a change in control.
	In accordance with accounting standards, compensation expense for non-vested stock options is recorded over the vesting period based on the fair value at the date of grant. The fair value of stock options on the date of grant is calculated using the Black-Scholes-Merton model and the assumptions listed below:
		February 2014 Grant			February 2013 Grant			February 2012 Grant
	Grant date price per share of option award	$	37.93		$	42.76		$	38.21
	Expected dividend yield per share		2.75	%		2.75	%		2.75	%
	Expected life in years		6.5			6.5			6.5
	Expected volatility		52.14	%		53.77	%		55.06	%
	Risk-free interest rate		1.98	%		1.29	%		1.34	%
	Grant date fair value per share of option awards	$	15.26		$	17.28		$	15.82
	The dividend yield is based on the Company’s current and prospective dividend rate which calculates a continuous dividend yield based upon the market price of the underlying common stock. The expected life in years is based on the simplified method permitted under Securities and Exchange Commission Staff Accounting Bulletin No. 14d.2 which calculates the average of the weighted vesting term and the contractual term of the option. This method was selected due to the lack of historical exercise data with respect to the Company. Expected volatility is based on the historical volatility of the Company’s common stock and the historical volatility of certain other similar public companies. The risk-free interest rate is based on U.S. Treasury bill rates for the expected life of the option.
	The following table shows a summary of the status and activity of stock options for the nine months ended September 30, 2014:
		Options			Weighted Average			Weighted Average			Aggregate Intrinsic
					Exercise Price			Remaining			Value (in millions)
					per Option			Contractual Term
								(in years)
	Outstanding at December 31, 2013		421,080		$	35.96
	Granted		106,658		$	37.93
	Exercised		(26,349	)	$	25.51
	Expired		(6,019	)	$	40.15
	Forfeited		(34,707	)	$	39.75
	Outstanding at September 30, 2014		460,663		$	36.67			6.83		$	0.7
	Exercisable at September 30, 2014		202,863		$	33			4.71		$	0.7
	Total stock-based compensation expense recognized for the three and nine months ended September 30, 2014 and 2013 is as follows:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
	(Dollars in millions)
	Stock-based compensation expense recognized:
	Selling, general and administrative expenses	$	1.4		$	1.9		$	4.6		$	4.7
	Less related income tax benefit		0.6			0.8			1.8			1.9
		$	0.8		$	1.1		$	2.8		$	2.8
	As of September 30, 2014, total future compensation expense related to non-vested stock-based compensation arrangements totaled $7.4 million and the weighted-average period over which this cost is expected to be recognized is approximately 23 months

Segment_Information

Segment Information	9 Months Ended
	Sep. 30, 2014
Segment Reporting [Abstract]	'
Segment Information	'
	9. Segment Information
	The Company has three reportable segments: Carbon Materials and Chemicals, Railroad and Utility Products and Services, and Performance Chemicals. The Company’s reportable segments contain business units that offer different products. The reportable segments are each managed separately because they manufacture and distribute distinct products with different production processes. The business units have been aggregated into three 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. Other rail services provided include bridge inspection, engineering, maintenance and repair, and construction services. Railroad services include bridge inspection and engineering services. Utility products include transmission and distribution poles and pilings.
	The Company’s Performance Chemicals segment develops, manufactures, and markets wood preservation chemicals and wood treatment technologies and services a diverse range of end-markets including infrastructure, residential and commercial construction, and agriculture.
	The Company 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,
			2014			2013			2014			2013
	(Dollars in millions)
	Revenues from external customers:
	Carbon Materials and Chemicals		$	226.6		$	241.6		$	637.8		$	692.4
	Railroad and Utility Products and Services			167.4			153.6			444.4			444.1
	Performance Chemicals			46.1			0			46.1			0
	Total		$	440.1		$	395.2		$	1,128.30		$	1,136.50
	Intersegment revenues:
	Carbon Materials and Chemicals		$	20.7		$	23.3		$	62		$	70.9
	Performance Chemicals			0.8			0			0.8			0
	Total		$	21.5		$	23.3		$	62.8		$	70.9
	Depreciation and amortization expense(a):
	Carbon Materials and Chemicals		$	6.6		$	4.5		$	18.7		$	13.5
	Railroad and Utility Products and Services			2.2			2.7			8.7			8.3
	Performance Chemicals			2.4			0			2.4			0
	Total		$	11.2		$	7.2		$	29.8		$	21.8
	Operating profit:
	Carbon Materials and Chemicals(b)		$	5.2		$	21.8		$	0.2		$	47.4
	Railroad and Utility Products and Services			17.4			17.8			41.3			46.6
	Performance Chemicals			1.3			0			1.3			0
	Corporate(c)			(6.6	)		(0.5	)		(11.7	)		(1.5	)
	Total		$	17.3		$	39.1		$	31.1		$	92.5
	(a)	Excludes impairment charges of $4.7 million for the nine months ended September 30, 2014 for Carbon Materials and Chemicals.
	(b)	Includes plant closure costs of $2.6 million and $13.4 million for the three and nine months ended September 30, 2014, respectively, for the Uithoorn, the Netherlands facility and impairment charges of $4.7 million for the nine months ended September 30, 2014 for the Tangshan, China facility.
	(c)	Operating loss for Corporate includes general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc., acquisition and acquisition-related integration costs.
	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,
			2014			2013
	(Dollars in millions)
	Segment assets:
	Carbon Materials and Chemicals		$	537.2		$	535.5
	Railroad and Utility Products and Services			293.8			179.3
	Performance Chemicals			474.3			0
	All other			48.6			70.1
	Total		$	1,353.90		$	784.9
	Goodwill:
	Carbon Materials and Chemicals		$	67.2		$	68
	Railroad and Utility Products and Services			12.8			4.7
	Performance Chemicals			158			0
	Total		$	238		$	72.7

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	10. Income Taxes
	Effective Tax Rate
	The income tax provision for interim periods is based on an estimated annual effective tax rate, which requires management to make its best estimate of annual pretax income by domestic and foreign jurisdictions and other items that impact taxable income. Items that are not related to annual pretax ordinary income are recognized entirely in the interim period as discrete items.
	Income taxes as a percentage of pretax income before discrete items was 94.2 percent and 46.4 percent for the three months ended September 30, 2014 and 2013, respectively. Discrete items included in income taxes for the three months ended September 30, 2014 consisted of a net tax benefit of $0.3 million primarily due to changes in unrecognized tax benefits. 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.
	The effective tax rate for the third quarter of 2014 differs from the U.S. federal statutory rate of 35.0 percent due to taxes on foreign earnings (+47.7 percent), nondeductible expenses (+11.0 percent), uncertain tax positions (+2.7 percent), and state taxes (+0.1 percent) partially offset by the domestic manufacturing deduction (-1.8 percent) and tax credits (-0.5 percent). With respect to the third quarter of 2013, the effective tax rate differs from the U.S. federal statutory rate of 35.0 percent due to 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).
	Income taxes as a percentage of pretax income before discrete items was 80.9 percent and 43.0 percent for the nine months ended September 30, 2014 and 2013, respectively. Discrete items included in income taxes for the nine months ended September 30, 2014 were a net tax benefit of $6.0 million which was primarily related to management’s decision that a deferred tax liability for certain undistributed earnings of its European subsidiaries was no longer necessary as these earnings are permanently reinvested. 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.
	The effective tax rate for the first nine months of 2014 differs from the U.S. federal statutory rate of 35.0 percent primarily due to the taxes on foreign earnings (+38.8 percent), nondeductible expenses (+6.7 percent), uncertain tax positions (+2.0 percent), and state taxes (+0.8 percent) partially offset by the domestic manufacturing deduction (-2.0 percent) and tax credits (-0.4 percent). With respect to the first nine months of 2013, the effective tax rate 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).
	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, and uncertain tax positions. To the extent that actual results vary from the estimates at the end of the third quarter, the actual tax provision recognized for 2014 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 2008.
	As of September 30, 2014 and December 31, 2013, the total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate, was approximately $4.5 million and $4.5 million, respectively. Unrecognized tax benefits totaled $5.8 million and $6.1 million as of September 30, 2014 and December 31, 2013, respectively. The Company recognizes interest expense and any related penalties from uncertain tax positions in income tax expense. As of September 30, 2014 and December 31, 2013 the Company had accrued approximately $1.4 million and $1.2 million for interest and penalties, respectively.

Inventories

Inventories	9 Months Ended
	Sep. 30, 2014
Inventory Disclosure [Abstract]	'
Inventories	'
	11. Inventories
	Net inventories as of September 30, 2014 and December 31, 2013 are summarized in the table below:
		September 30,		December 31,
		2014		2013
	(Dollars in millions)
	Raw materials	$	151.1	$	105.4
	Work in process		19.7		19.2
	Finished goods		111.9		94.8
			282.7		219.4
	Less revaluation to LIFO		55		50.6
	Net	$	227.7	$	168.8

Property_Plant_and_Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2014
Property, Plant and Equipment [Abstract]	'
Property, Plant and Equipment	'
	12. Property, Plant and Equipment
	Property, plant and equipment as of September 30, 2014 and December 31, 2013 are summarized in the table below:
		September 30,		December 31,
		2014		2013
	(Dollars in millions)
	Land	$	19.4	$	9.1
	Buildings		45		30.6
	Machinery and equipment		676.8		608.1
			741.2		647.8
	Less accumulated depreciation		454.4		450.8
	Net	$	286.8	$	197
	Impairment – Impairment charges for the nine months ended September 30, 2014 were $4.7 million ($2.8 million, net of non-controlling interest) and were related to the Carbon Material and Chemicals’ plant in Tangshan, China. This impairment charge was calculated using a probability-weighted discounted cash flow model.
	The impairment of the Company’s 60-percent owned plant in Tangshan, China is due to the forced closure of a neighboring metallurgical coke facility. In October 2013, the Company was informed by the Tangshan Municipal People’s Government (“Tangshan Government”) of its intention to close the two coke batteries owned and operated by the Tangshan Iron and Steel Group Co., Ltd (“TISCO”) in Tangshan, China. The Tangshan Government has ordered the closure of these coke batteries in an effort to improve the air quality in the Tangshan area. One TISCO coke battery closed in March 2014 and the Company has been informed that the remaining TISCO coke battery will cease production sometime within the next twelve to eighteen months.
	The Company’s 60-percent owned subsidiary, Koppers (China) Carbon & Chemical Company Limited (“KCCC”) is located near to TISCO’s coke facility and relies on its operations for a significant portion of raw material supply, utilities and other shared services. Closure of the TISCO coke batteries directly impacts KCCC’s ability to operate its coal tar distillation plant and the Company has determined that it is unable to continue coal tar distillation activities at the site once TISCO ceases production activities at the adjacent facility. The Company is continuing to evaluate its options, which include transitioning to a new location or entering into other strategic partnerships with other unrelated coal tar distillation companies.
	The closure of KCCC’s coal tar distillation facility would have a material adverse effect on the Company’s business, financial condition, cash flow and results of operations. For the most recent year ended December 31, 2013, KCCC contributed operating profit of approximately $3.3 million after deducting profit attributable to non-controlling interests and excluding asset impairment charges. As of September 30, 2014, all fixed assets directly related to the facility have been substantially depreciated.
	The Company believes it would be able to continue fulfilling current domestic Chinese customers and its export commitments with capacity at Koppers (Jiangsu) Carbon Chemical Company Limited, which commenced production in July 2014, its other 30-percent owned Chinese company and other commercial relationships in China. However, the Company’s margin on export sales may be negatively affected as a result of these actions.

Pensions_and_Postretirement_Be

Pensions and Postretirement Benefit Plans	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Pensions and Postretirement Benefit Plans	'
	13. Pensions and Postretirement Benefit Plans
	The Company and its subsidiaries maintain a number of defined benefit and defined contribution plans to provide retirement benefits for employees in the U.S., as well as employees outside the U.S. These plans are maintained and contributions are made in accordance with the Employee Retirement Income Security Act of 1974, 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, 2014 and 2013:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
	(Dollars in millions)
	Service cost	$	0.7		$	0.9		$	1.9		$	2.6
	Interest cost		2.8			2.7			8.8			8
	Expected return on plan assets		(3.5	)		(3.2	)		(10.5	)		(9.5	)
	Amortization of prior service cost		0			0			(0.1	)		0.1
	Amortization of net loss		1			1.9			3			5.7
	Net periodic benefit cost	$	1		$	2.3		$	3.1		$	6.9
	Defined contribution plan expense	$	1.3		$	1.2		$	4.5		$	4.1
	Other postretirement benefit plans		0.1			0.1			0.3			0.3
	Multi-employer pension plan expense		0			0.1			0.2			0.4

Debt

Debt	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Debt	'
	14. Debt
	Debt at September 30, 2014 and December 31, 2013 was as follows:
		Weighted			Maturity		September 30,		December 31,
		Average					2014		2013
		Interest Rate
	(Dollars in millions)
	Term Loan		3.64	%		2019	$	300	$	0
	Revolving Credit Facility		3.64	%		2019		214.9		0
	Construction loans		6.12	%		2018		55.7		6.6
	Senior Notes		7  7/8	%		2019		296.9		296.5
	Total debt							867.5		303.1
	Less short term debt and current maturities of long-term debt							30		0
	Long-term debt						$	837.5	$	303.1
	Revolving Credit Facility and Term Loan
	On August 15, 2014, Koppers Inc. replaced its $350.0 million revolving credit facility with a new $500.0 senior secured revolving credit facility and a $300.0 million senior secured term loan to finance its acquisition of the Osmose Entities. Both borrowings mature on August 15, 2019. The interest rates on the new borrowings are variable and are based on LIBOR. The initial interest rate on the borrowings at August 15, 2014 was 3.25 percent. The senior secured term loan has quarterly principal repayment obligations of 2.5 percent of the original principal amount borrowed, or $7.5 million.
	Borrowings under the revolving credit facility and term loan 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 and term loan contain certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends, investments or acquisitions. In addition, such covenants give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios.
	As of September 30, 2014, the Company had $233.0 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, 2014, $52.1 million of commitments were utilized by outstanding letters of credit.
	Construction Loans
	On November 18, 2013, the Company’s 75-percent owned subsidiary, Koppers (Jiangsu) Carbon Chemical Company Limited (“KJCC”) entered into two committed loan facility agreements for a combined commitment of RMB 265 million or approximately $44 million. The third party bank provided facility has a commitment amount of RMB 198.8 million and the other committed facility of RMB 66.2 million is provided by the 25-percent non-controlling shareholder in KJCC. Borrowings under the third party bank facility are secured by a letter of credit issued by a bank under the Koppers Inc. revolving credit facility. The committed facilities were used to finance the costs related to the construction of the coal tar distillation plant in Pizhou, Jiangsu province in China. The facilities are variable rate and have certain financial covenants that monitor minimum net worth and leverage. KJCC will repay the loans in six installments every six months starting in May 2016 with a final repayment on November 18, 2018, the maturity date of the loans.
	Senior Notes
	The Koppers Inc. 7 7/8 percent Senior Notes due 2019 (the “Senior Notes”) were issued on December 1, 2009 at an offering price of 98.311 percent of face value, or $294.9 million and have a principal amount at maturity of $300.0 million. The Senior Notes have an effective interest rate yield of 8 1/8 percent per annum. The 2009 Senior Notes are our senior obligations, are fully and unconditionally guaranteed by KH and certain of our wholly-owned domestic subsidiaries, and, as of August 15, 2014, are secured equally and ratably with the obligations under our Senior Secured Credit Facilities.
	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, 2014
Asset Retirement Obligation Disclosure [Abstract]	'
Asset Retirement Obligations	'
	15. Asset Retirement Obligations
	The Company recognizes asset retirement obligations for the removal and disposal of residues; dismantling of certain tanks required by governmental authorities; cleaning and dismantling costs for owned rail cars; and cleaning costs for leased rail cars and barges. The following table reflects changes in the carrying values of asset retirement obligations:
		September 30,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	23.2		$	21.5
	Accretion expense		1.8			1.2
	Revision in estimated cash flows, net		4.3			6.7
	Cash expenditures		(2.3	)		(5.6	)
	Currency translation		(0.1	)		(0.6	)
	Balance at end of period	$	26.9		$	23.2

Deferred_Revenue_from_Extended

Deferred Revenue from Extended Product Warranty Liabilities	9 Months Ended
	Sep. 30, 2014
Deferred Revenue Disclosure [Abstract]	'
Deferred Revenue from Extended Product Warranty Liabilities	'
	16. Deferred Revenue from Extended Product Warranty Liabilities
	The Company defers revenues associated with extended product warranty liabilities based on historical loss experience and sales of extended warranties on certain products. The following table reflects changes in the carrying values of deferred revenue:
		September 30,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	3.2		$	3.9
	Revenue earned		(0.5	)		(0.7	)
	Balance at end of period	$	2.7		$	3.2

Derivative_Financial_Instrumen

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Financial Instruments	'
	17. Derivative Financial Instruments
	The Company utilizes derivative instruments to manage exposures to risks that have been identified and measured and are capable of being controlled. The primary risks managed by the company by using derivative instruments are commodity price risk associated with copper and foreign currency exchange risk associated with a number of currencies, principally the U.S. dollar, the Canadian dollar, the Euro and British pounds. Swap contracts on copper are used to manage the price risk associated with forecasted purchases of materials used in the Company’s manufacturing processes. The Company enters into foreign currency forward contracts to manage foreign currency risk associated with the Company’s receivable and payable balances. Generally, the Company enters into master netting arrangements with the counterparties and offsets net derivative positions with the same counterparties. Currently, the Company’s agreements do not require cash collateral.
	ASC Topic 815-10, “Derivatives and Hedging,” requires companies to recognize all derivative instruments as either assets or liabilities at fair value in the balance sheet. Derivative instruments’ fair value is determined using significant other observable inputs, or Level 2 in the fair value hierarchy. In accordance with ASC Topic 815-10, the Company designates commodity swaps as cash flow hedges of forecasted purchases of commodities. For derivative instruments that are designated and qualify as cash flow hedges, the effective portion of the gain or loss on the derivative is reported as a component of other comprehensive income and is reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative instruments representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current earnings.
	As of September 30, 2014, the Company has outstanding copper swap contracts totaling 21.9 million pounds and the fair value of these swap contracts was $(3.3) million which is classified in accrued liabilities in the condensed consolidated balance sheet. The amount of loss recognized in other comprehensive income totaled $1.9 million, net of tax, at September 30, 2014. The ineffective portion of the copper swap contracts totaled $0.1 million and was charged to cost of sales for the three and nine months ended September 30, 2014. In the next twelve months the Company estimates that $1.3 million of unrealized losses, net of tax, related to commodity price hedging will be reclassified from other comprehensive income into earnings.
	Forward contracts related to foreign currency are not designated as hedges and fair value changes in these contracts are immediately charged to earnings and are classified in other income in the condensed consolidated statement of income. As of September 30, 2014, the Company has outstanding foreign currency forward contracts with a net fair value totaling $(0.1) million, of which $0.3 million is classified in accrued liabilities and $0.2 million is classified in other current assets in the condensed consolidated balance sheet.

Commitments_and_Contingent_Lia

Commitments and Contingent Liabilities	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingent Liabilities	'
	18. Commitments and Contingent Liabilities
	The Company and its subsidiaries are involved in litigation and various proceedings relating to environmental laws and regulations 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 two states in which the plaintiffs claim they suffered a variety of illnesses (including cancer) as a result of exposure to coal tar pitch sold by the defendants. There are approximately 112 plaintiffs in 60 cases pending as of September 30, 2014 as compared to 111 plaintiffs in 61 cases pending as of December 31, 2013. As of September 30, 2014, there are a total of 59 cases pending in state court in Pennsylvania, and one case pending in state court in Tennessee. Koppers Inc. has been dismissed from three cases formerly pending in state court in Arkansas.
	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 59 cases filed in Pennsylvania state court seek unspecified damages in excess of the court’s minimum jurisdictional limit. 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. The district court dismissed Koppers Holdings Inc. in September 2013 on the ground that there was no personal jurisdiction. Plaintiffs’ appeal of the dismissal of Koppers Holdings Inc. was dismissed in December 2013. In May 2014, the Court entered an amended scheduling order for class certification, which sets a deadline of November 21, 2014 for completion of class factual discovery with expert witness discovery to follow. Discovery on the merits is stayed until further order of the court.
	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.
	Virgin Islands. Koppers Performance Chemicals Inc. (“KPC”) is currently a defendant in a putative class action lawsuit filed in the United States District Court of the Virgin Islands. The plaintiffs claim, on behalf of themselves and others similarly situated, that KPC’s wood preservative products and formulas are defective, and the complaint alleges the following causes of action: breach of contract, negligence, strict liability, fraud and violation of Virgin Islands Consumer Fraud and Deceptive Business Practices statute. The putative class is defined as all users (residential or commercial) of wood products treated with KPC wood preserving products in the United States who purchased such wood products from January 1, 2004 to the present. Alternatively, plaintiffs allege that the putative class should be all persons and entities that have owned or acquired buildings or other structures physically located in the U.S. Virgin Islands that contain wood products treated with KPC wood preserving products from January 1, 2004 to the present. The complaint alleges plaintiffs are entitled to unspecified “economic and compensatory damages”, punitive damages, costs and disgorgement of profits. The complaint further requests a declaratory judgment and injunction to establish an inspection and disposal program for class members’ structures. The lawsuit was filed on July 16, 2014, and KPC has filed a motion to dismiss. Plaintiffs have not yet responded to KPC’s motion to dismiss. 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.
	Other Matters. In July 2012, Koppers Netherlands B.V.’s (“Koppers Netherlands”) coal tar distillation plant suffered a series of electrical disruptions which significantly affected plant operations and prevented the resumption of plant operations for a period of approximately three weeks. As a result of the suspension of operations, the coal tar distillation plant was unable to provide steam and other services to an adjacent unaffiliated plant. This unaffiliated plant and Koppers Netherlands’ plant share certain services and plant infrastructure under a cost sharing agreement. In September 2012, Koppers Netherlands received a business interruption claim from the owner of the unaffiliated plant that included an initial claim for lost profits of approximately $1.7 million. In July 2013 the owner of the unaffiliated plant filed a request for arbitration with the Netherlands Arbitration Institute seeking damages for the business interruption claim plus interest, costs and legal fees. In its statement of claim to the arbitration board, the owner of the unaffiliated facility has claimed damages of at least $3.1 million for these costs. The arbitration hearing was held in June 2014 and a decision is not expected until late 2014 or 2015.
	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. Currently, at the properties acquired from Beazer East (which include all but two of the sites permitted under the Resource Conservation and Recovery Act (“RCRA”)), a significant portion of all investigative, cleanup and closure activities are being conducted and paid for by Beazer East pursuant to the terms of the Indemnity. In addition, other of Koppers Inc.’s sites are or have been operated under RCRA and various other environmental permits, and remedial and closure activities are being conducted at some of these sites.
	To date, the parties that retained, assumed and/or agreed to indemnify the Company against the liabilities referred to above, including Beazer East, have performed their obligations in all material respects. The Company believes that, for the last three years ended December 31, 2013, amounts paid by Beazer East as a result of its environmental remediation obligations under the Indemnity have averaged in total approximately $15 million per year. Periodically, issues have arisen between Koppers Inc. and Beazer East and/or other indemnitors that have been resolved without arbitration. Koppers Inc. and Beazer East engage in discussions from time to time that involve, among other things, the allocation of environmental costs related to certain operating and closed facilities.
	If for any reason (including disputed coverage or financial incapability) one or more of such parties fail to perform their obligations and the Company or its subsidiaries are held liable for or otherwise required to pay all or part of such liabilities without reimbursement, the imposition of such liabilities on the Company or its subsidiaries could have a material adverse effect on its business, financial condition, cash flows and results of operations. Furthermore, the Company could be required to record a contingent liability on its balance sheet with respect to such matters, which could result in a negative impact to the Company’s business, financial condition, cash flows and results of operations.
	Domestic Environmental Matters. Koppers Inc. has been named as one of the potentially responsible parties (“PRPs”) at the Portland Harbor CERCLA site located on the Willamette River in Oregon. Koppers Inc. currently maintains a coal tar pitch terminal near the site. Koppers Inc. has responded to an Environmental Protection Agency (“EPA”) information request and has executed a PRP agreement which outlines the process to develop an allocation of past and future costs among more than 80 parties to the site. Koppers Inc. believes it is a de minimus contributor at the site. Additionally, a separate natural resources damages assessment (“NRDA”) is being conducted by a local trustee group. The NRDA is intended to identify further information necessary to estimate liabilities for remediation based settlements of national resource damages (“NRD”) claims. Koppers Inc. may also incur liabilities under the NRD process and has entered into a separate process to develop an allocation of NRDA cost.
	In March 2012, a draft Feasibility Study (“FS”) was submitted to EPA by the Lower Willamette Group, a group of certain PRPs which has been conducting the investigation of the site. The draft FS identifies ten possible remedial alternatives which range in cost from approximately $170 million to $1.8 billion. The FS does not determine who is responsible for remediation costs or select remedies. The FS is under review by the EPA which will issue a final decision on the nature and extent of the final remediation. Responsibility for implementing and funding that work will be decided in the separate allocation process.
	In September 2009, Koppers Inc. received a general notice letter notifying it that it may be a PRP at the Newark Bay CERCLA site. In January 2010, Koppers Inc. submitted a response to the general notice letter asserting that Koppers Inc. is a de minimus party at this site.
	Other than the estimated costs of participating in the PRP group at the Portland Harbor and Newark Bay CERCLA sites totaling $0.8 million at September 30, 2014, the Company has not provided a reserve for these matters because there has not been a determination of the total cost of the investigations, the remediation that will be required, the amount of natural resources damages or how those costs will be allocated among the PRPs. Accordingly, the Company believes that it cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. An unfavorable resolution of these matters may have a material adverse effect on the Company’s business, financial condition, cash flows and results of operations.
	Australian Environmental Matters. Soil and groundwater contamination has been detected at certain of the Company’s Australian facilities. At the Company’s tar distillation facility in Newcastle, New South Wales, Australia, soil contamination from an abandoned underground coal tar pipeline and other groundwater contamination have been detected at a property adjacent to the facility. In 2011, the Company and the owner of the adjacent property reached an agreement in which the Company will contribute $1.6 million and the owner of the adjacent property will contribute $7.5 million toward remediation of the property. The agreement provides that the Company will assume responsibility for the management of the remediation effort and will indemnify the current owner for any remediation costs in excess of its agreed contribution. At the completion of the remediation, the agreement provides that the property will be transferred to the Company. The remediation project commenced in 2011 and the Company has reserved its expected remaining remediation costs of $1.9 million and has recorded a receivable, net of cash collections, from the owner of the adjacent property of $1.8 million as of September 30, 2014.
	In December 2011, the Company ceased manufacturing operations at its Continental Carbon facility located in Kurnell, Australia. The Company has accrued its expected cost of site remediation resulting from the closure of $5.5 million as of September 30, 2014.
	Environmental Reserves Rollforward. The following table reflects changes in the accrued liability for environmental matters, of which $6.7 million and $8.2 million are classified as current liabilities at September 30, 2014 and December 31, 2013, respectively:
		Period ended
		September 30,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	11.9		$	14.1
	Expense		0.4			1.8
	Reversal of reserves		(0.2	)		(1.2	)
	Cash expenditures		(2.6	)		(0.9	)
	Acquisition		0.8			0
	Currency translation		0			(1.9	)
	Balance at end of period	$	10.3		$	11.9

Subsidiary_Guarantor_Informati

Subsidiary Guarantor Information for Koppers Inc. Senior Notes	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Subsidiary Guarantor Information for Koppers Inc. Senior Notes	'
	19. Subsidiary Guarantor Information for Koppers Inc. Senior Notes
	On December 1, 2009, Koppers Inc. issued $300.0 million principal value of Senior Notes. Koppers Holdings and each of Koppers Inc.’s 100 percent-owned material domestic subsidiaries other than Koppers Assurance, Inc. fully and unconditionally guarantee the payment of principal and interest on the Senior Notes. The domestic guarantor subsidiaries include Koppers World-Wide Ventures Corporation, Koppers Delaware, Inc., Koppers Concrete Products, Inc., Concrete Partners, Inc., Koppers Performance Chemicals Inc., Koppers Railroad Structures Inc., Osmose NZ, LLC, Osmose-Nevada Limited Liability Company, Wood Protection LP, Wood Protection Management LLC and Koppers Asia LLC. Non-guarantor subsidiaries are owned directly or indirectly by Koppers Inc. or are owned directly or indirectly by Koppers World-Wide Ventures Corporation.
	The guarantee of a guarantor subsidiary will be automatically and unconditionally released and discharged in the event of:
		¡		any sale of the capital stock or substantially all of the assets of the guarantor subsidiary;
		¡		the designation of the guarantor subsidiary as an unrestricted subsidiary in accordance with the indenture governing the Senior Notes; and
		¡		the legal defeasance, covenant defeasance or satisfaction and discharge of the indenture governing the Senior Notes.
	Koppers Holdings depends on the dividends from the earnings of Koppers Inc. and its subsidiaries to generate the funds necessary to meet its financial obligations, including the payment of any declared dividend of Koppers Holdings. Koppers Inc.’s credit agreement prohibits it from making dividend payments to Koppers Holdings Inc. unless (1) such dividend payments are permitted by the indenture governing Koppers Inc.’s Senior Notes and (2) no event of default or potential default has occurred or is continuing under the credit agreement. The indenture governing Koppers Inc.’s Senior Notes restricts its ability to finance Koppers Holdings Inc.’s payment of dividends if (1) a default has occurred or would result from such financing, (2) a restricted subsidiary of Koppers Inc. which is not a guarantor under the indenture is not able to incur additional indebtedness (as defined in the indenture), and (3) the sum of all restricted payments (as defined in the indenture) have exceeded the permitted amount (referred to as the “basket”) at such point in time.
	The Koppers Inc. revolving credit facility agreement provides for a revolving credit facility of up to $500.0 million at variable rates. Borrowings under the revolving credit facility are secured by a first priority lien on substantially all of the assets of Koppers Inc. and its material domestic subsidiaries. The revolving credit facility contains certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends, investments or acquisitions. In addition, such covenants give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios.
	The amount of restricted net assets unavailable for distribution to Koppers Holdings Inc. by Koppers Inc. totals $75 million as of September 30, 2014. Cash dividends paid to Koppers Holdings Inc. by its subsidiaries totaled $17.8 million and $33.2 million for the nine months ended September 30, 2014 and 2013, respectively.
	Separate condensed consolidating financial statement information for Koppers Holdings Inc. (the parent), Koppers Inc., domestic guarantor subsidiaries and non-guarantor subsidiaries as of September 30, 2014 and December 31, 2013 and for the three and nine months ended September 30, 2014 and 2013 is as follows. The condensed consolidating statement of comprehensive income for the three and nine months ended September 30, 2013 has been restated to revise the presentation of net income and related investments in subsidiaries under the equity method of accounting. This restatement changed the previously reported amounts for equity income, other income, interest expense, net income attributable to Koppers, comprehensive income attributable to Koppers and other related subtotals in the following columns: Parent, Koppers Inc., Domestic Guarantor Subsidiaries and Consolidating Adjustments. There was no change to amounts previously reported for the Consolidated totals.
	The condensed consolidating statement of cash flows for the nine months ended September 30, 2013 has been restated to revise the presentation of intercompany dividends and intercompany lending agreements. This restatement changed the previously reported amounts for cash provided by or used in operating activities, investing activities and financing activities in the following columns: Koppers Inc., Domestic Guarantor Subsidiaries, Non-Guarantor Subsidiaries and Consolidating Adjustments. There was no change to amounts previously reported for the Parent or Consolidated columns except for rounding differences. There was no impact on the net increase or decrease in cash for any column.
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2014
			Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
									Guarantor			Subsidiaries			Adjustments
									Subsidiaries
	(Dollars in millions)
	Net sales		$	0		$	220.5		$	53.3		$	189.6		$	(23.3	)	$	440.1
	Cost of sales including depreciation and amortization			0			194.8			43.1			175.8			(22.9	)		390.8
	Selling, general and administrative			0.3			16.8			5.1			9.8			0			32
	Operating profit (loss)			(0.3	)		8.9			5.1			4			(0.4	)		17.3
	Other income (expense)			0			0			1.3			(0.3	)		(1.2	)		(0.2	)
	Equity income of subsidiaries			(2.6	)		6.5			0.3			0			(4.2	)		0
	Interest expense (income)			0			11.4			0			1.7			(1.2	)		11.9
	Income taxes			(0.2	)		6.6			0.2			2.9			0			9.5
	Income from continuing operations			(2.7	)		(2.6	)		6.5			(0.9	)		(4.6	)		(4.3	)
	Discontinued operations			0			0			0			0.1			0			0.1
	Noncontrolling interests			0			0			0			(1.5	)		0			(1.5	)
	Net income attributable to Koppers		$	(2.7	)	$	(2.6	)	$	6.5		$	0.7		$	(4.6	)	$	(2.7	)
	Comprehensive income attributable to Koppers		$	(18.6	)	$	(18.4	)	$	(10.1	)	$	(9.6	)	$	38.1		$	(18.6	)
	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)			0			0.4			1			0.8			(0.9	)		1.3
	Equity income of subsidiaries			19.4			14.2			8.2			0			(41.8	)		0
	Interest expense (income)			0			6.8			0			0.8			(0.9	)		6.7
	Income taxes			(0.2	)		10.2			0			4.1			0			14.1
	Income from continuing operations			19.1			19.4			13.8			9			(41.7	)		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		$	19.4		$	13.8		$	8.5		$	(41.7	)	$	19.1
	Comprehensive income attributable to Koppers		$	25.8		$	26		$	19.3		$	5.3		$	(50.6	)	$	25.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2014
			Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
									Guarantor			Subsidiaries			Adjustments
									Subsidiaries
	(Dollars in millions)
	Net sales		$	0		$	600.5		$	71.2		$	501		$	(44.4	)	$	1,128.30
	Cost of sales including depreciation and amortization			0			539.7			52.3			474.1			(44.2	)		1,021.90
	Selling, general and administrative			1.3			44.6			5.7			23.7			0			75.3
	Operating profit (loss)			(1.3	)		16.2			13.2			3.2			(0.2	)		31.1
	Other income (expense)			0			0.1			3.1			(0.2	)		(3.3	)		(0.3	)
	Equity income of subsidiaries			1.9			16.1			(6.7	)		0			(11.3	)		0
	Interest expense (income)			0			24.7			0			3.9			(3.3	)		25.3
	Income taxes			(0.5	)		5.8			(5.7	)		9.5			0			9.1
Income from continuing operations			1.1			1.9			15.3			(10.4	)		(11.5	)		(3.6	)
Discontinued operations			0			0			0			(0.0	)		0			0
Noncontrolling interests			0			0			0			(4.7	)		0			(4.7	)
Net income attributable to Koppers		$	1.1		$	1.9		$	15.3		$	(5.7	)	$	(11.5	)	$	1.1
Comprehensive income attributable to Koppers		$	(9.2	)	$	(8.3	)	$	3.5		$	(14.7	)	$	19.5		$	(9.2	)
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)			0			1.3			3.1			1.5			(3.1	)		2.8
Equity income of subsidiaries			45.4			35.7			18.3			0			(99.4	)		0
Interest expense (income)			0			20.3			0			3			(3.1	)		20.2
Income taxes			(0.6	)		21.3			0.2			8.4			0			29.3
Income from continuing operations			44.5			45.4			34.7			20.5			(99.3	)		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		$	45.4		$	34.7		$	19.2		$	(99.3	)	$	44.5
Comprehensive income attributable to Koppers		$	40.8		$	41.6		$	27.7		$	(0.4	)	$	(68.9	)	$	40.8
Condensed Consolidating Balance Sheet
September 30, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents		$	0		$	0.2		$	1.8		$	73.1		$	0		$	75.1
Receivables, net			0			91.3			35.8			108.8			0			235.9
Affiliated receivables			0.1			4.1			8.3			10.4			(22.9	)		0
Inventories, net			0			87.8			31.5			108.8			(0.4	)		227.7
Deferred tax assets			0			7.9			10.9			1.4			0			20.2
Other current assets			0			5.5			1.5			42.1			0			49.1
Total current assets			0.1			196.8			89.8			344.6			(23.3	)		608
Equity investments			153.3			832.1			247.9			3.8			(1,231.4	)		5.7
Property, plant and equipment, net			0			111.9			51.9			123			0			286.8
Goodwill			0			39.8			162.7			35.5			0			238
Intangible assets, net			0			2.4			162.7			15			0			180.1
Deferred tax assets			0			0.5			1.1			8.7			0			10.3
Affiliated loan receivables			0			32.6			155.9			41.5			(230.0	)		0
Other noncurrent assets			0			19.4			3.7			1.9			0			25
Total assets		$	153.4		$	1,235.50		$	875.7		$	574		$	(1,484.7	)	$	1,353.90
LIABILITIES AND EQUITY
Accounts payable		$	0.1		$	52.2		$	8.3		$	61.8		$	0		$	122.4
Affiliated payables			0			14			6.3			8.4			(28.7	)		0
Accrued liabilities			4.7			33.8			19.9			49.3			0			107.7
Short-term debt and current portion of long-term debt			0			30			0			0			0			30
Total current liabilities			4.8			130			34.5			119.5			(28.7	)		260.1
Long-term debt			0			781.8			0			55.7			0			837.5
Affiliated debt			0			121			32.6			76.4			(230.0	)		0
Other long-term liabilities			0			55.2			10.8			25.3			0			91.3
Total liabilities			4.8			1,088.00			77.9			276.9			(258.7	)		1,188.90
Koppers shareholders’ equity			148.6			147.5			797.8			280.7			(1,226.0	)		148.6
Noncontrolling interests			0			0			0			16.4			0			16.4
Total liabilities and equity		$	153.4		$	1,235.50		$	875.7		$	574		$	(1,484.7	)	$	1,353.90
Condensed Consolidating Balance Sheet
December 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents		$	0		$	29.9		$	0.1		$	52.2		$	0		$	82.2
Receivables, net			0			75.6			9.3			82			0			166.9
Affiliated receivables			0.2			1.1			3.9			2.3			(7.5	)		0
Inventories, net			0			86.1			0			82.9			(0.2	)		168.8
Deferred tax assets			0			7.9			1.5			0.6			0			10
Other current assets			0			7.3			0.6			37.3			0			45.2
Total current assets			0.2			207.9			15.4			257.3			(7.7	)		473.1
Equity investments			174.7			333.5			182.9			4.6			(689.1	)		6.6
Property, plant and equipment, net			0			112.2			0			84.8			0			197
Goodwill			0			39.8			0			32.9			0			72.7
Intangible assets, net			0			3.3			0			8.9			0			12.2
Deferred tax assets			0			2.4			(1.4	)		8.3			0			9.3
Affiliated loan receivables			0			8.5			123.8			40.9			(173.2	)		0
Other noncurrent assets			0			11.7			0			2.3			0			14
Total assets		$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
LIABILITIES AND EQUITY
Accounts payable		$	0		$	48.3		$	6.7		$	52.6		$	0		$	107.6
Affiliated payables			0			1.9			4			8.6			(14.5	)		0
Accrued liabilities			5.1			27.8			0.5			54.1			0			87.5
Total current liabilities			5.1			78			11.2			115.3			(14.5	)		195.1
Long-term debt			0			296.5			0			6.6			0			303.1
Affiliated debt			0			109.5			8.5			55.2			(173.2	)		0
Other long-term liabilities			0			67.6			2.5			26.8			0			96.9
Total liabilities			5.1			551.6			22.2			203.9			(187.7	)		595.1
Koppers shareholders’ equity			169.8			167.7			298.5			216.1			(682.3	)		169.8
Noncontrolling interests			0			0			0			20			0			20
Total liabilities and equity		$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
Condensed Consolidating Statement of Cash Flows
For the Nine Months Ended September 30, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities		$	16.5		$	(0.9	)	$	26.4		$	-4.5		$	(26.7	)	$	10.8
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions			0			(508.0	)		(15.1	)		(47.2	)		14.8			(555.5	)
(Loans to) repayments from affiliates			0			(24.4	)		(33.9	)		(0.5	)		58.8			0
Net cash proceeds (payments) from divestitures and asset sales			0			0.1			0			0			0			0.1
Net cash provided by (used in) investing activities			0			(532.3	)		(49.0	)		(47.7	)		73.6			(555.4	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt			0			514.9			0			48.9			0			563.8
Borrowings (repayments) of affiliated debt			0			17.5			24.3			17			(58.8	)		0
Deferred financing costs			0			(11.1	)		0			0			0			(11.1	)
Other financing activities			0			0			0			1.4			0			1.4
Dividends paid			(15.2	)		(17.8	)		0			(8.9	)		26.7			(15.2	)
Stock issued (repurchased)			(1.3	)		0			0			14.8			(14.8	)		(1.3	)
Net cash provided by (used in) financing activities			(16.5	)		503.5			24.3			73.2			(46.9	)		537.6
Effect of exchange rates on cash			0			0			0			(0.1	)		0			(0.1	)
Net increase (decrease) in cash and cash equivalents			0			(29.7	)		1.7			20.9			0			(7.1	)
Cash and cash equivalents at beginning of year			0			29.9			0.1			52.2			0			82.2
Cash and cash equivalents at end of period		$	0		$	0.2		$	1.8		$	73.1		$	0		$	75.1
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		$	43.7		$	2.5		$	23.1		$	(36.3	)	$	65.6
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions			0			(13.3	)		0			(16.1	)		0			(29.4	)
(Loans to) repayments from affiliates			0			(3.0	)		(5.5	)		(3.2	)		11.7			0
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			(14.9	)		(5.5	)		(18.3	)		11.7			(27.0	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of affiliated debt			0			8.7			3			0			(11.7	)		0
Deferred financing costs			0			(1.2	)		0			0			0			(1.2	)
Other financing activities			0			0			0			2.3			0			2.3
Dividends paid			(15.3	)		(33.2	)		0			(3.1	)		36.3			(15.3	)
Stock issued (repurchased)			(17.3	)		0			0			0			0			(17.3	)
Net cash provided by (used in) financing activities			(32.6	)		(25.7	)		3			(0.8	)		24.6			(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

Subsidiary_Guarantor_Informati1

Subsidiary Guarantor Information for Shelf Registration	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Subsidiary Guarantor Information for Shelf Registration	'
	20. Subsidiary Guarantor Information for Shelf Registration
	Under a registration statement on Form S-3, Koppers Holdings may sell a combination of securities, including common stock, debt securities, preferred stock, depository shares, warrants and units, from time to time in one or more offerings. In addition, Koppers Inc. may sell debt securities from time to time under the registration statement. Debt securities may be fully and unconditionally guaranteed, on a joint and several basis, by Koppers Holdings, Koppers Inc. and/or other guarantor subsidiaries which will correspond to certain subsidiaries in the United States, Europe and Australia which are 100 percent owned by either Koppers Holdings or Koppers Inc. The non-guarantor subsidiaries consist of certain subsidiaries in the United States, China, India and Mauritius. Non-guarantor subsidiaries are owned directly by Koppers Inc. or are owned directly or indirectly by foreign guarantor subsidiaries. The guarantor subsidiaries that issue guarantees, if any, will be determined when a debt offering actually occurs under the registration statement and accordingly, the condensed consolidating financial information for subsidiary guarantors will be revised to identify the subsidiaries that actually provided guarantees. These guarantees will be governed pursuant to a supplemental indenture which the trustee and the issuing company would enter into concurrent with the debt offering.
	Koppers Holdings depends on the dividends from the earnings of Koppers Inc. and its subsidiaries to generate the funds necessary to meet its financial obligations, including the payment of any declared dividend of Koppers Holdings. Koppers Inc.’s credit agreement prohibits it from making dividend payments to Koppers Holdings Inc. unless (1) such dividend payments are permitted by the indenture governing Koppers Inc.’s Senior Notes and (2) no event of default or potential default has occurred or is continuing under the credit agreement. The indenture governing Koppers Inc.’s Senior Notes restricts its ability to finance Koppers Holdings Inc.’s payment of dividends if (1) a default has occurred or would result from such financing, (2) a restricted subsidiary of Koppers Inc. which is not a guarantor under the indenture is not able to incur additional indebtedness (as defined in the indenture), and (3) the sum of all restricted payments (as defined in the indenture) have exceeded the permitted amount (referred to as the “basket”) at such point in time.
	The Koppers Inc. revolving credit facility agreement provides for a revolving credit facility of up to $500.0 million at variable rates. Borrowings under the revolving credit facility are secured by a first priority lien on substantially all of the assets of Koppers Inc. and its material domestic subsidiaries. The revolving credit facility contains certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends, investments or acquisitions. In addition, such covenants give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios.
	The amount of restricted net assets unavailable for distribution to Koppers Holdings Inc. by Koppers Inc. totals $75 million as of September 30, 2014. Cash dividends paid to Koppers Holdings Inc. by its subsidiaries totaled $17.8 million and $33.2 million for the nine months ended September 30, 2014 and 2013, respectively.
	Separate condensed consolidating financial statement information for the parent, Koppers Inc., domestic guarantor subsidiaries, foreign guarantor subsidiaries and non-guarantor subsidiaries as of September 30, 2014 and December 31, 2013 and for the three and nine months ended September 30, 2014 and 2013 is as follows. The condensed consolidating statement of comprehensive income for the three and nine months ended September 30, 2013 has been restated to revise the presentation of net income and related investments in subsidiaries under the equity method of accounting. This restatement changed the previously reported amounts for equity income, other income, interest expense, net income attributable to Koppers, comprehensive income attributable to Koppers and other related subtotals in the following columns: Koppers Inc., Domestic Guarantor Subsidiaries, Foreign Guarantor Subsidiaries and Consolidating Adjustments. There was no change to amounts previously reported for the Consolidated totals.
	The condensed consolidating statement of cash flows for the nine months ended September 30, 2013 has been restated to revise the presentation of intercompany dividends and intercompany lending agreements. This restatement changed the previously reported amounts for cash provided by or used in operating activities, investing activities and financing activities in the following columns: Koppers Inc., Domestic Guarantor Subsidiaries, Foreign Guarantor Subsidiaries, Non-Guarantor Subsidiaries and Consolidating Adjustments. There was no change to amounts previously reported for the Parent or Consolidated columns except for rounding differences. There was no impact on the net increase or decrease in cash for any column.
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	220.5		$	17.1		$	103		$	121.7		$	(22.2	)	$	440.1
	Cost of sales including depreciation and amortization		0			194.8			13.6			91			113.4			(22.0	)		390.8
	Selling, general and administrative		0.3			16.8			0.2			5.2			9.5			0			32
	Operating profit (loss)		(0.3	)		8.9			3.3			6.8			(1.2	)		(0.2	)		17.3
	Other income (expense)		0			0			1.2			0			(0.3	)		(1.1	)		(0.2	)
	Equity income of subsidiaries		(2.6	)		6.5			(0.4	)		(4.1	)		(0.1	)		0.7			0
	Interest expense (income)		0			11.4			0			1			0.6			(1.1	)		11.9
	Income taxes		(0.2	)		6.6			0.2			2.5			0.4			0			9.5
	Income from continuing operations		(2.7	)		(2.6	)		3.9			(0.8	)		(2.6	)		0.5			(4.3	)
	Discontinued operations		0			0			0			0			0.1			0			0.1
	Noncontrolling interests		0			0			0			0			(1.5	)		0			(1.5	)
	Net income attributable to Koppers	$	(2.7	)	$	(2.6	)	$	3.9		$	(0.8	)	$	(1.0	)	$	0.5		$	(2.7	)
	Comprehensive income attributable to Koppers	$	(18.6	)	$	(18.4	)	$	(12.4	)	$	(10.4	)	$	(5.9	)	$	47.1		$	(18.6	)
	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		$	120.8		$	43.3		$	(10.9	)	$	395.2
	Cost of sales including depreciation and amortization		0			197.5			7.2			103.7			40.4			(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)		0			0.4			1			0.7			0.1			(0.9	)		1.3
	Equity income of subsidiaries		19.4			14.2			8.2			0.4			0.1			(42.3	)		0
	Interest expense (income)		0			6.8			0			0.7			0			(0.8	)		6.7
	Income taxes		(0.2	)		10.2			0			3.8			0.3			0			14.1
	Income from continuing operations		19.1			19.4			13.8			8.2			1.4			(42.3	)		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		$	19.4		$	13.8		$	8.1		$	1		$	(42.3	)	$	19.1
	Comprehensive income attributable to Koppers	$	25.8		$	26		$	14.5		$	13.7		$	2.9		$	(57.1	)	$	25.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	600.5		$	35		$	321.1		$	215.3		$	(43.6	)	$	1,128.30
	Cost of sales including depreciation and amortization		0			539.7			22.8			291.7			211.3			(43.6	)		1,021.90
	Selling, general and administrative		1.3			44.6			0.8			16.4			12.2			0			75.3
	Operating profit (loss)		(1.3	)		16.2			11.4			13			(8.2	)		0			31.1
	Other income (expense)		0			0.1			3			0.1			(0.3	)		(3.2	)		(0.3	)
	Equity income of subsidiaries		1.9			16.1			(7.4	)		(9.2	)		0			(1.4	)		0
	Interest expense (income)		0			24.7			0			2.4			1.4			(3.2	)		25.3
	Income taxes		(0.5	)		5.8			(5.7	)		8.9			0.6			0			9.1
	Income from continuing operations		1.1			1.9			12.7			(7.4	)		(10.5	)		(1.4	)		(3.6	)
	Discontinued operations		0			0			0			0			0			0			0
	Noncontrolling interests		0			0			0			0			(4.7	)		0			(4.7	)
	Net income attributable to Koppers	$	1.1		$	1.9		$	12.7		$	(7.4	)	$	(5.8	)	$	(1.4	)	$	1.1
Comprehensive income attributable to Koppers	$	(9.2	)	$	(8.3	)	$	1.1		$	(14.4	)	$	(6.5	)	$	28.1		$	(9.2	)
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		$	348.7		$	123.8		$	(44.8	)	$	1,136.50
Cost of sales including depreciation and amortization		0			580.6			34.3			305.8			116			(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)		0			1.3			3.1			0.8			0.7			(3.1	)		2.8
Equity income of subsidiaries		45.4			35.7			18.3			1.4			0.1			(100.9	)		0
Interest expense (income)		0			20.3			0			2.5			0.5			(3.1	)		20.2
Income taxes		(0.6	)		21.3			0.2			7.4			1			0			29.3
Income from continuing operations		44.5			45.4			34.7			18.4			3.6			(100.8	)		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		$	45.4		$	34.7		$	18.3		$	2.4		$	(100.8	)	$	44.5
Comprehensive income attributable to Koppers	$	40.8		$	41.6		$	22.8		$	15.8		$	2.9		$	(83.1	)	$	40.8
Condensed Consolidating Balance Sheet
September 30, 2014
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0			$0.20			$0.10			$31.90			$42.90			$0.00			$75.10
Receivables, net		0			91.3			10.7			43.1			90.8			0			235.9
Affiliated Receivables		0.1			4.1			(2.8	)		6.4			12.9			(20.7	)		0
Inventories, net		0			87.8			0			66.9			73.2			(0.2	)		227.7
Deferred tax assets		0			7.9			3.9			0			8.4			0			20.2
Other current assets		0			5.5			0.4			12.7			30.5			0			49.1
Total current assets		0.1			196.8			12.3			161			258.7			(20.9	)		608
Equity investments		153.3			832.1			175.5			44.9			3.8			(1,203.9	)		5.7
Property, plant and equipment, net		0			111.9			0.9			40			134			0			286.8
Goodwill		0			39.8			0			30.7			167.5			0			238
Intangible assets, net		0			2.4			0			8.3			169.4			0			180.1
Deferred tax assets		0			0.5			2.3			5.1			2.4			0			10.3
Affiliated loan receivables		0			32.6			155.9			0.1			41.4			(230.0	)		0
Other noncurrent assets		0			19.4			0			0.8			4.7			0.1			25
Total assets	$	153.4		$	1,235.50		$	346.9		$	290.9		$	781.9		$	(1,454.7	)	$	1,353.90
LIABILITIES AND EQUITY
Accounts payable	$	0.1		$	52.2		$	0		$	28		$	42.1		$	0		$	122.4
Affiliated payables		0			14			6.3			2.5			3.7			(26.5	)		0
Accrued liabilities		4.7			33.8			0.4			29			39.8			0			107.7
Short-term debt and current portion of long-term debt		0			30			0			0			0			0			30
Total current liabilities		4.8			130			6.7			59.5			85.6			(26.5	)		260.1
Long-term debt		0			781.8			0			0			55.7			0			837.5
Affiliated debt		0			121			32.6			54.7			21.7			(230.0	)		0
Other long-term liabilities		0			55.2			2.5			17.7			15.8			0.1			91.3
Total liabilities		4.8			1,088.00			41.8			131.9			178.8			(256.4	)		1,188.90
Koppers shareholders’ equity		148.6			147.5			305.1			159			586.7			(1,198.3	)		148.6
Noncontrolling interests		0			0			0			0			16.4			0			16.4
Total liabilities and equity	$	153.4		$	1,235.50		$	346.9		$	290.9		$	781.9		$	(1,454.7	)	$	1,353.90
Condensed Consolidating Balance Sheet
December 31, 2013
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0		$	29.9		$	0.1		$	43.5		$	8.7		$	0		$	82.2
Receivables, net		0			75.6			9.3			55.5			26.5			0			166.9
Affiliated receivables		0.2			1.1			3.9			0.8			1.6			(7.6	)		0
Inventories, net		0			86.1			0			75.2			7.7			(0.2	)		168.8
Deferred tax assets		0			7.9			1.5			0			0.6			0			10
Other current assets		0			7.3			0.6			17.5			19.8			0			45.2
Total current assets		0.2			207.9			15.4			192.5			64.9			(7.8	)		473.1
Equity investments		174.7			333.5			182.9			50.5			4.5			(739.5	)		6.6
Property, plant and equipment, net		0			112.2			0			38.1			46.7			0			197
Goodwill		0			39.8			0			31.5			1.4			0			72.7
Intangible assets, net		0			3.3			0			8.9			0			0			12.2
Deferred tax assets		0			2.4			(1.4	)		5.5			2.8			0			9.3
Affiliated loan receivables		0			8.5			123.8			0.1			40.8			(173.2	)		0
Other noncurrent assets		0			11.7			0			1			1.3			0			14
Total assets	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
LIABILITIES AND EQUITY
Accounts payable	$	0		$	48.3		$	6.7		$	40.6		$	12		$	0		$	107.6
Affiliated payables		0			1.9			4			0.4			8.4			(14.7	)		0
Accrued liabilities		5.1			27.8			0.5			31.4			22.7			0			87.5
Total current liabilities		5.1			78			11.2			72.4			43.1			(14.7	)		195.1
Long-term debt		0			296.5			0			0			6.6			0			303.1
Affiliated debt		0			109.5			8.5			55.2			0			(173.2	)		0
Other long-term liabilities		0			67.6			2.5			19.6			7.2			0			96.9
Total liabilities		5.1			551.6			22.2			147.2			56.9			(187.9	)		595.1
Koppers shareholders’ equity		169.8			167.7			298.5			180.9			85.5			(732.6	)		169.8
Noncontrolling interests		0			0			0			0			20			0			20
Total liabilities and equity	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
Condensed Consolidating Statement of Cash Flows
For the Nine Months Ended September 30, 2014
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities	$	16.5		$	(0.9	)	$	19.1		$	11.4		$	-8.6		$	(26.7	)	$	10.8
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(508.0	)		(15.7	)		(14.1	)		(36.6	)		18.9			(555.5	)
(Loans to) repayments from affiliates		0			(24.4	)		(27.7	)		0			(6.7	)		58.8			0
Net cash proceeds (payments) from divestitures and asset sales		0			0.1			0			0			0			0			0.1
Net cash provided by (used in) investing activities		0			(532.3	)		(43.4	)		(14.1	)		(43.3	)		77.7			(555.4	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0			514.9			0			0			48.9			0			563.8
Borrowings (repayments) of affiliated debt		0			17.5			24.3			0			17			(58.8	)		0
Deferred financing costs		0			(11.1	)		0			0			0			0			(11.1	)
Other financing activities		0			0			0			0			1.4			0			1.4
Dividends paid		(15.2	)		(17.8	)		0			(8.9	)		0			26.7			(15.2	)
Stock issued (repurchased)		(1.3	)		0			0			0			18.9			(18.9	)		(1.3	)
Net cash provided by (used in) financing activities		(16.5	)		503.5			24.3			(8.9	)		86.2			(51.0	)		537.6
Effect of exchange rates on cash		0			0			0			0			(0.1	)		0			(0.1	)
Net increase (decrease) in cash and cash equivalents		0			(29.7	)		0			(11.6	)		34.2			0			(7.1	)
Cash and cash equivalents at beginning of year		0			29.9			0.1			43.5			8.7			0			82.2
Cash and cash equivalents at end of period	$	0		$	0.2		$	0.1		$	31.9		$	42.9		$	0		$	75.1
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		$	43.7		$	2.5		$	25.8		$	(2.7	)	$	(36.3	)	$	65.6
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(13.3	)		0			(14.3	)		(9.5	)		7.7			(29.4	)
(Loans to) repayments from affiliates		0			(3.0	)		(5.5	)		0			(3.2	)		11.7			0
Net cash proceeds (payments) from divestitures and asset sales		0			1.4			0			1			0			0			2.4
Net cash provided by (used in) investing activities		0			(14.9	)		(5.5	)		(13.3	)		(12.7	)		19.4			(27.0	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of affiliated debt		0			8.7			3			0			0			(11.7	)		0
Deferred financing costs		0			(1.2	)		0			0			0			0			(1.2	)
Other financing activities		0			0			0			0			2.3			0			2.3
Dividends paid		(15.3	)		(33.2	)		0			(3.1	)		0			36.3			(15.3	)
Stock issued (repurchased)		(17.3	)		0			0			0			7.7			(7.7	)		(17.3	)
Net cash provided by (used in) financing activities		(32.6	)		(25.7	)		3			(3.1	)		10			16.9			(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

Related_Party_Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2014
Related Party Transactions [Abstract]	'
Related Party Transactions	'
	21. Related Party Transactions
	As of September 30, 2014, the Company has loaned $9.5 million to TKK, a 30-percent owned company in China. The loan is repayable in November 2014 and is expected to be extended for an additional one-year term.

New_Accounting_Pronouncements

New Accounting Pronouncements	9 Months Ended
	Sep. 30, 2014
Accounting Changes and Error Corrections [Abstract]	'
New Accounting Pronouncements	'
	22. New Accounting Pronouncements
	In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606).” ASU 2014-09 requires an entity to recognize revenue in a manner that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve that core principle, the amendment provides five steps that an entity should apply when recognizing revenue. The amendment also specifies the accounting of some costs to obtain or fulfill a contract with a customer and expands the disclosure requirements around contracts with customers. An entity can either adopt this amendment retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of initially applying the update recognized at the date of initial application. The amendment is effective for annual reporting periods beginning after December 15, 2016. Early adoption is not permitted. The Company is currently evaluating the impact of the adoption of ASU 2014-09 on the Company’s financial statements.
	In August 2014, the FASB issued ASU No. 2014-15, “Disclosure of Uncertainties About an Entity’s Ability to Continue as a Going Concern” (“ASU 2014-15”), which requires management to perform interim and annual assessments of an entity’s ability to continue as a going concern within one year of the date the financial statements are issued and provides guidance on determining when and how to disclose going concern uncertainties in the financial statements. Certain disclosures will be required if conditions give rise to substantial doubt about an entity’s ability to continue as a going concern. ASU 2014-15 applies to all entities and is effective for annual and interim reporting periods ending after December 15, 2016, with early adoption permitted. We do not expect that the adoption of this standard will have a material effect on the Company’s financial statements.

New_Accounting_Pronouncements_

New Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Changes and Error Corrections [Abstract]	'
New Accounting Pronouncements	'
	In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606).” ASU 2014-09 requires an entity to recognize revenue in a manner that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve that core principle, the amendment provides five steps that an entity should apply when recognizing revenue. The amendment also specifies the accounting of some costs to obtain or fulfill a contract with a customer and expands the disclosure requirements around contracts with customers. An entity can either adopt this amendment retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of initially applying the update recognized at the date of initial application. The amendment is effective for annual reporting periods beginning after December 15, 2016. Early adoption is not permitted. The Company is currently evaluating the impact of the adoption of ASU 2014-09 on the Company’s financial statements.
	In August 2014, the FASB issued ASU No. 2014-15, “Disclosure of Uncertainties About an Entity’s Ability to Continue as a Going Concern” (“ASU 2014-15”), which requires management to perform interim and annual assessments of an entity’s ability to continue as a going concern within one year of the date the financial statements are issued and provides guidance on determining when and how to disclose going concern uncertainties in the financial statements. Certain disclosures will be required if conditions give rise to substantial doubt about an entity’s ability to continue as a going concern. ASU 2014-15 applies to all entities and is effective for annual and interim reporting periods ending after December 15, 2016, with early adoption permitted. We do not expect that the adoption of this standard will have a material effect on the Company’s financial statements.

Plant_Closures_and_Discontinue1

Plant Closures and Discontinued Operations (Tables)	9 Months Ended
	Sep. 30, 2014
Discontinued Operations and Disposal Groups [Abstract]	'
Summary of Restructuring Activities and Related Reserves	'
	Details of the restructuring activities and related reserves are as follows:
		Severance and			Environmental			Site			Other			Total
		employee benefits			remediation			demolition
	(Dollars in millions)
	Reserve at December 31, 2012	$	0.2		$	6.7		$	6.3		$	0.1		$	13.3
	Reversal of accrued charges		(0.1	)		0			(0.3	)		0			(0.4	)
	Cash paid		0			(0.1	)		(2.0	)		(0.1	)		(2.2	)
	Currency translation		0			(1.0	)		(0.7	)		0			(1.7	)
	Reserve at December 31, 2013	$	0.1		$	5.6		$	3.3		$	0		$	9
	Accrual		10			0			3.1			0			13.1
	Cash paid		(9.3	)		0			(0.2	)		0			(9.5	)
	Currency translation		(0.2	)		(0.1	)		(0.1	)		0			(0.4	)
	Reserve at September 30, 2014	$	0.6		$	5.5		$	6.1		$	0		$	12.2

Business_Acquisitions_Tables

Business Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Schedule of Company's Preliminary Fair Value Estimates for Osmose Entities	'
	The following table summarizes the Company’s preliminary fair value estimates for the Osmose entities as of September 30, 2014:
	(Dollars in millions)	Initial
		Allocation
	Cash and cash equivalents	$	27.2
	Accounts receivable, net		60
	Inventories, net		51.9
	Other current assets		9.5
	Property, plant and equipment		59.6
	Goodwill		164.8
	Intangible assets		164.2
	Other assets		4
	Total assets acquired		541.2
	Accounts payable		21.2
	Accrued liabilities		17.4
	Other liabilities		8.5
	Total liabilities assumed		47.1
	Net assets acquired	$	494.1
Summary of Company's Revenue And Net Income From Continuing Operations	'
	The following unaudited pro forma information presents a summary of the Company’s revenues and net income from continuing operations as if the acquisition occurred on January 1, 2013 (the first day of the most recently completed fiscal year). The unaudited pro forma information is not necessarily indicative of operating results that would have been achieved had the acquisition been completed as of January 1, 2013 and does not intend to project the future financial results of the Company after the acquisition of the Osmose Entities. The unaudited pro forma information is based on certain assumptions, which management believes are reasonable, and do not reflect the cost of any integration activities or the benefits from the acquisition and synergies that may be derived from any integration activities.
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	(Dollars in millions)
	Revenue	$	500.1	$	498.4	$	1,392.90	$	1,433.00
	Income from continuing operations attributable to Koppers		3.4		23.2		16.4		45.1

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Schedule of Company's Financial Instruments	'
	Carrying amounts and the related estimated fair values of the Company’s financial instruments as of September 30, 2014 and December 31, 2013 are as follows:
		September 30, 2014				December 31, 2013
		Fair Value		Carrying		Fair Value		Carrying
				Value				Value
	(Dollars in millions)
	Financial assets:
	Cash and cash equivalents, including restricted cash	$	75.1	$	75.1	$	82.2	$	82.2
	Investments and other assets(a)		1.4		1.4		1.4		1.4
	Financial liabilities:
	Long-term debt (including current portion)	$	883.7	$	867.5	$	331.2	$	303.1

Comprehensive_Income_and_Equit1

Comprehensive Income and Equity (Tables)	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Schedule of Comprehensive Income	'
	Total comprehensive income for the three and nine months ended September 30, 2014 and 2013 is summarized in the table below:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
	(Dollars in millions)
	Net (loss) income	$	(4.2	)	$	19.5		$	(3.6	)	$	45.7
	Other comprehensive (loss) income:
	Change in currency translation adjustment		(10.6	)		5.6			(9.8	)		(0.4	)
	Change in foreign currency transactions of long-term subsidiary investments		(3.8	)		0.3			(0.5	)		(6.6	)
	Change in derivative financial instrument net loss, net of tax benefit of $(0.8), $0.0, $(0.8) and $0.0		(1.9	)		0			(1.9	)		0
	Change in unrecognized pension net loss, net of tax expense of $0.2, $0.8, $0.7 and $2.3		0.6			1.2			1.8			3.5
	Change in unrecognized prior service cost, net of tax expense of $0.0, $0.0, $0.0 and $0.0		0			0			(0.1	)		0.1
	Total comprehensive (loss) income		(19.9	)		26.6			(14.1	)		42.3
	Less: comprehensive (loss) income attributable to noncontrolling interests		(1.3	)		0.8			(4.9	)		1.5
	Comprehensive (loss) income attributable to Koppers	$	(18.6	)	$	25.8		$	(9.2	)	$	40.8
Schedule of Change in Equity	'
	The following tables present the change in equity for the nine months ended September 30, 2014 and 2013, respectively:
	(Dollars in millions)	Total Koppers			Noncontrolling			Total Equity
		Shareholders’			Interests
		Equity
	Balance at December 31, 2013	$	169.8		$	20		$	189.8
	Net income (loss)		1.1			(4.7	)		(3.6	)
	Issuance of common stock		0.7			0			0.7
	Employee stock plans		4.9			0			4.9
	Other comprehensive income (loss)		(10.3	)		(0.2	)		(10.5	)
	Dividends		(15.6	)		0			(15.6	)
	Investment in noncontrolling interests		0			1.3			1.3
	Repurchases of common stock		(2.0	)		0			(2.0	)
	Balance at September 30, 2014	$	148.6		$	16.4		$	165
	(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 (loss) income		(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

Earnings_per_Common_Share_Tabl

Earnings per Common Share (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Schedule of Computation of Basic and Diluted Earnings per Common Share	'
	The following table sets forth the computation of basic and diluted earnings per common share:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014		2013
	(Dollars in millions, except share amounts, in thousands, and per share amounts)
	Net (loss) income attributable to Koppers	$	(2.7	)	$	19.1		$	1.1	$	44.5
	Less: income (loss) from discontinued operations		0.1			(0.1	)		0		(0.1	)
	(Loss) Income from continuing operations attributable to Koppers	$	(2.8	)	$	19.2		$	1.1	$	44.6
	Weighted average common shares outstanding:
	Basic		20,495			20,577			20,452		20,657
	Effect of dilutive securities		108			224			141		230
	Diluted		20,603			20,801			20,593		20,887
	(Loss) earnings per common share – continuing operations:
	Basic (loss) earnings per common share	$	(0.14	)	$	0.93		$	0.05	$	2.16
	Diluted (loss) earnings per common share		(0.14	)		0.92			0.05		2.13
	Other data:
	Antidilutive securities excluded from computation of diluted earnings per common share		265			254			260		236

Stockbased_Compensation_Tables

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Summary of Performance Stock Units	'
	The following table shows a summary of the performance stock units as of September 30, 2014:
	Performance Period	Minimum			Target			Maximum
		Shares			Shares			Shares
	2012 – 2014		0			87,059			130,559
	2013 – 2015		0			85,207			127,811
	2014 – 2016		0			102,149			153,224
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, 2014:
		Restricted			Performance			Total			Weighted Average
		Stock Units			Stock Units			Stock Units			Grant Date Fair
											Value per Unit
	Non-vested at December 31, 2013		148,836			319,984			468,820		$	40.3
	Granted		95,067			108,506			203,573		$	37.9
	Credited from dividends		3,813			8,425			12,238		$	38.52
	Vested		(57,102	)		(132,317	)		(189,419	)	$	40.18
	Forfeited		(12,695	)		(24,218	)		(36,913	)	$	39.51
	Non-vested at September 30, 2014		177,919			280,380			458,299		$	39.3
Stock Options Fair Value Assumptions	'
	The fair value of stock options on the date of grant is calculated using the Black-Scholes-Merton model and the assumptions listed below:
		February 2014 Grant			February 2013 Grant			February 2012 Grant
	Grant date price per share of option award	$	37.93		$	42.76		$	38.21
	Expected dividend yield per share		2.75	%		2.75	%		2.75	%
	Expected life in years		6.5			6.5			6.5
	Expected volatility		52.14	%		53.77	%		55.06	%
	Risk-free interest rate		1.98	%		1.29	%		1.34	%
	Grant date fair value per share of option awards	$	15.26		$	17.28		$	15.82
Summary of Status and Activity of Stock Options	'
	The following table shows a summary of the status and activity of stock options for the nine months ended September 30, 2014:
		Options			Weighted Average			Weighted Average			Aggregate Intrinsic
					Exercise Price			Remaining			Value (in millions)
					per Option			Contractual Term
								(in years)
	Outstanding at December 31, 2013		421,080		$	35.96
	Granted		106,658		$	37.93
	Exercised		(26,349	)	$	25.51
	Expired		(6,019	)	$	40.15
	Forfeited		(34,707	)	$	39.75
	Outstanding at September 30, 2014		460,663		$	36.67			6.83		$	0.7
	Exercisable at September 30, 2014		202,863		$	33			4.71		$	0.7
Schedule of Stock-based Compensation Expense Recognized	'
	Total stock-based compensation expense recognized for the three and nine months ended September 30, 2014 and 2013 is as follows:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
	(Dollars in millions)
	Stock-based compensation expense recognized:
	Selling, general and administrative expenses	$	1.4		$	1.9		$	4.6		$	4.7
	Less related income tax benefit		0.6			0.8			1.8			1.9
		$	0.8		$	1.1		$	2.8		$	2.8

Segment_Information_Tables

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2014
Segment Reporting [Abstract]	'
Summary of Results of Segment Operations	'
	The following table sets forth certain sales and operating data, net of all intersegment transactions, for the Company’s segments for the periods indicated:
			Three Months Ended September 30,						Nine Months Ended September 30,
			2014			2013			2014			2013
	(Dollars in millions)
	Revenues from external customers:
	Carbon Materials and Chemicals		$	226.6		$	241.6		$	637.8		$	692.4
	Railroad and Utility Products and Services			167.4			153.6			444.4			444.1
	Performance Chemicals			46.1			0			46.1			0
	Total		$	440.1		$	395.2		$	1,128.30		$	1,136.50
	Intersegment revenues:
	Carbon Materials and Chemicals		$	20.7		$	23.3		$	62		$	70.9
	Performance Chemicals			0.8			0			0.8			0
	Total		$	21.5		$	23.3		$	62.8		$	70.9
	Depreciation and amortization expense(a):
	Carbon Materials and Chemicals		$	6.6		$	4.5		$	18.7		$	13.5
	Railroad and Utility Products and Services			2.2			2.7			8.7			8.3
	Performance Chemicals			2.4			0			2.4			0
	Total		$	11.2		$	7.2		$	29.8		$	21.8
	Operating profit:
	Carbon Materials and Chemicals(b)		$	5.2		$	21.8		$	0.2		$	47.4
	Railroad and Utility Products and Services			17.4			17.8			41.3			46.6
	Performance Chemicals			1.3			0			1.3			0
	Corporate(c)			(6.6	)		(0.5	)		(11.7	)		(1.5	)
	Total		$	17.3		$	39.1		$	31.1		$	92.5
	(a)	Excludes impairment charges of $4.7 million for the nine months ended September 30, 2014 for Carbon Materials and Chemicals.
	(b)	Includes plant closure costs of $2.6 million and $13.4 million for the three and nine months ended September 30, 2014, respectively, for the Uithoorn, the Netherlands facility and impairment charges of $4.7 million for the nine months ended September 30, 2014 for the Tangshan, China facility.
	(c)	Operating loss for Corporate includes general and administrative costs for Koppers Holdings Inc., the parent company of Koppers Inc., acquisition and acquisition-related integration costs.
Summary of Tangible and Intangible Assets by Segments	'
	The following table sets forth certain tangible and intangible assets allocated to each of the Company’s segments as of the dates indicated:
			September 30,			December 31,
			2014			2013
	(Dollars in millions)
	Segment assets:
	Carbon Materials and Chemicals		$	537.2		$	535.5
	Railroad and Utility Products and Services			293.8			179.3
	Performance Chemicals			474.3			0
	All other			48.6			70.1
	Total		$	1,353.90		$	784.9
	Goodwill:
	Carbon Materials and Chemicals		$	67.2		$	68
	Railroad and Utility Products and Services			12.8			4.7
	Performance Chemicals			158			0
	Total		$	238		$	72.7

Inventories_Tables

Inventories (Tables)	9 Months Ended
	Sep. 30, 2014
Inventory Disclosure [Abstract]	'
Components of Inventories	'
	Net inventories as of September 30, 2014 and December 31, 2013 are summarized in the table below:
		September 30,		December 31,
		2014		2013
	(Dollars in millions)
	Raw materials	$	151.1	$	105.4
	Work in process		19.7		19.2
	Finished goods		111.9		94.8
			282.7		219.4
	Less revaluation to LIFO		55		50.6
	Net	$	227.7	$	168.8

Property_Plant_and_Equipment_T

Property, Plant and Equipment (Tables)	9 Months Ended
	Sep. 30, 2014
Property, Plant and Equipment [Abstract]	'
Property, Plant and Equipment	'
	Property, plant and equipment as of September 30, 2014 and December 31, 2013 are summarized in the table below:
		September 30,		December 31,
		2014		2013
	(Dollars in millions)
	Land	$	19.4	$	9.1
	Buildings		45		30.6
	Machinery and equipment		676.8		608.1
			741.2		647.8
	Less accumulated depreciation		454.4		450.8
	Net	$	286.8	$	197

Pensions_and_Postretirement_Be1

Pensions and Postretirement Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans	'
	The following table provides the components of net periodic benefit cost for the pension plans and other benefit plans for the three and nine months ended September 30, 2014 and 2013:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
	(Dollars in millions)
	Service cost	$	0.7		$	0.9		$	1.9		$	2.6
	Interest cost		2.8			2.7			8.8			8
	Expected return on plan assets		(3.5	)		(3.2	)		(10.5	)		(9.5	)
	Amortization of prior service cost		0			0			(0.1	)		0.1
	Amortization of net loss		1			1.9			3			5.7
	Net periodic benefit cost	$	1		$	2.3		$	3.1		$	6.9
	Defined contribution plan expense	$	1.3		$	1.2		$	4.5		$	4.1
	Other postretirement benefit plans		0.1			0.1			0.3			0.3
	Multi-employer pension plan expense		0			0.1			0.2			0.4

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Schedule of Long-Term Debt Instruments	'
	Debt at September 30, 2014 and December 31, 2013 was as follows:
		Weighted			Maturity		September 30,		December 31,
		Average					2014		2013
		Interest Rate
	(Dollars in millions)
	Term Loan		3.64	%		2019	$	300	$	0
	Revolving Credit Facility		3.64	%		2019		214.9		0
	Construction loans		6.12	%		2018		55.7		6.6
	Senior Notes		7  7/8	%		2019		296.9		296.5
	Total debt							867.5		303.1
	Less short term debt and current maturities of long-term debt							30		0
	Long-term debt						$	837.5	$	303.1

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2014
Asset Retirement Obligation Disclosure [Abstract]	'
Schedule of Changes in Carrying Values of 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,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	23.2		$	21.5
	Accretion expense		1.8			1.2
	Revision in estimated cash flows, net		4.3			6.7
	Cash expenditures		(2.3	)		(5.6	)
	Currency translation		(0.1	)		(0.6	)
	Balance at end of period	$	26.9		$	23.2

Deferred_Revenue_from_Extended1

Deferred Revenue from Extended Product Warranty Liabilities (Tables)	9 Months Ended
	Sep. 30, 2014
Deferred Revenue Disclosure [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,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	3.2		$	3.9
	Revenue earned		(0.5	)		(0.7	)
	Balance at end of period	$	2.7		$	3.2

Commitments_and_Contingent_Lia1

Commitments and Contingent Liabilities (Tables)	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Changes in Accrued Liability for Environmental Matters	'
	The following table reflects changes in the accrued liability for environmental matters, of which $6.7 million and $8.2 million are classified as current liabilities at September 30, 2014 and December 31, 2013, respectively:
		Period ended
		September 30,			December 31,
		2014			2013
	(Dollars in millions)
	Balance at beginning of year	$	11.9		$	14.1
	Expense		0.4			1.8
	Reversal of reserves		(0.2	)		(1.2	)
	Cash expenditures		(2.6	)		(0.9	)
	Acquisition		0.8			0
	Currency translation		0			(1.9	)
	Balance at end of period	$	10.3		$	11.9

Subsidiary_Guarantor_Informati2

Subsidiary Guarantor Information for Koppers Inc. Senior Notes (Tables) (Senior Notes [Member])	9 Months Ended
	Sep. 30, 2014
Senior Notes [Member]	'
Condensed Consolidating Statement of Comprehensive Income	'
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	220.5		$	53.3		$	189.6		$	(23.3	)	$	440.1
	Cost of sales including depreciation and amortization		0			194.8			43.1			175.8			(22.9	)		390.8
	Selling, general and administrative		0.3			16.8			5.1			9.8			0			32
	Operating profit (loss)		(0.3	)		8.9			5.1			4			(0.4	)		17.3
	Other income (expense)		0			0			1.3			(0.3	)		(1.2	)		(0.2	)
	Equity income of subsidiaries		(2.6	)		6.5			0.3			0			(4.2	)		0
	Interest expense (income)		0			11.4			0			1.7			(1.2	)		11.9
	Income taxes		(0.2	)		6.6			0.2			2.9			0			9.5
	Income from continuing operations		(2.7	)		(2.6	)		6.5			(0.9	)		(4.6	)		(4.3	)
	Discontinued operations		0			0			0			0.1			0			0.1
	Noncontrolling interests		0			0			0			(1.5	)		0			(1.5	)
	Net income attributable to Koppers	$	(2.7	)	$	(2.6	)	$	6.5		$	0.7		$	(4.6	)	$	(2.7	)
	Comprehensive income attributable to Koppers	$	(18.6	)	$	(18.4	)	$	(10.1	)	$	(9.6	)	$	38.1		$	(18.6	)
	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)		0			0.4			1			0.8			(0.9	)		1.3
	Equity income of subsidiaries		19.4			14.2			8.2			0			(41.8	)		0
	Interest expense (income)		0			6.8			0			0.8			(0.9	)		6.7
	Income taxes		(0.2	)		10.2			0			4.1			0			14.1
	Income from continuing operations		19.1			19.4			13.8			9			(41.7	)		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		$	19.4		$	13.8		$	8.5		$	(41.7	)	$	19.1
	Comprehensive income attributable to Koppers	$	25.8		$	26		$	19.3		$	5.3		$	(50.6	)	$	25.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	600.5		$	71.2		$	501		$	(44.4	)	$	1,128.30
	Cost of sales including depreciation and amortization		0			539.7			52.3			474.1			(44.2	)		1,021.90
	Selling, general and administrative		1.3			44.6			5.7			23.7			0			75.3
	Operating profit (loss)		(1.3	)		16.2			13.2			3.2			(0.2	)		31.1
	Other income (expense)		0			0.1			3.1			(0.2	)		(3.3	)		(0.3	)
	Equity income of subsidiaries		1.9			16.1			(6.7	)		0			(11.3	)		0
	Interest expense (income)		0			24.7			0			3.9			(3.3	)		25.3
	Income taxes		(0.5	)		5.8			(5.7	)		9.5			0			9.1
	Income from continuing operations		1.1			1.9			15.3			(10.4	)		(11.5	)		(3.6	)
	Discontinued operations		0			0			0			(0.0	)		0			0
	Noncontrolling interests		0			0			0			(4.7	)		0			(4.7	)
	Net income attributable to Koppers	$	1.1		$	1.9		$	15.3		$	(5.7	)	$	(11.5	)	$	1.1
	Comprehensive income attributable to Koppers	$	(9.2	)	$	(8.3	)	$	3.5		$	(14.7	)	$	19.5		$	(9.2	)
	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)		0			1.3			3.1			1.5			(3.1	)		2.8
Equity income of subsidiaries		45.4			35.7			18.3			0			(99.4	)		0
Interest expense (income)		0			20.3			0			3			(3.1	)		20.2
Income taxes		(0.6	)		21.3			0.2			8.4			0			29.3
Income from continuing operations		44.5			45.4			34.7			20.5			(99.3	)		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		$	45.4		$	34.7		$	19.2		$	(99.3	)	$	44.5
Comprehensive income attributable to Koppers	$	40.8		$	41.6		$	27.7		$	(0.4	)	$	(68.9	)	$	40.8
Condensed Consolidating Balance Sheet	'
	Condensed Consolidating Balance Sheet
	September 30, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	0.2		$	1.8		$	73.1		$	0		$	75.1
	Receivables, net		0			91.3			35.8			108.8			0			235.9
	Affiliated receivables		0.1			4.1			8.3			10.4			(22.9	)		0
	Inventories, net		0			87.8			31.5			108.8			(0.4	)		227.7
	Deferred tax assets		0			7.9			10.9			1.4			0			20.2
	Other current assets		0			5.5			1.5			42.1			0			49.1
	Total current assets		0.1			196.8			89.8			344.6			(23.3	)		608
	Equity investments		153.3			832.1			247.9			3.8			(1,231.4	)		5.7
	Property, plant and equipment, net		0			111.9			51.9			123			0			286.8
	Goodwill		0			39.8			162.7			35.5			0			238
	Intangible assets, net		0			2.4			162.7			15			0			180.1
	Deferred tax assets		0			0.5			1.1			8.7			0			10.3
	Affiliated loan receivables		0			32.6			155.9			41.5			(230.0	)		0
	Other noncurrent assets		0			19.4			3.7			1.9			0			25
	Total assets	$	153.4		$	1,235.50		$	875.7		$	574		$	(1,484.7	)	$	1,353.90
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	52.2		$	8.3		$	61.8		$	0		$	122.4
	Affiliated payables		0			14			6.3			8.4			(28.7	)		0
	Accrued liabilities		4.7			33.8			19.9			49.3			0			107.7
	Short-term debt and current portion of long-term debt		0			30			0			0			0			30
	Total current liabilities		4.8			130			34.5			119.5			(28.7	)		260.1
	Long-term debt		0			781.8			0			55.7			0			837.5
	Affiliated debt		0			121			32.6			76.4			(230.0	)		0
	Other long-term liabilities		0			55.2			10.8			25.3			0			91.3
	Total liabilities		4.8			1,088.00			77.9			276.9			(258.7	)		1,188.90
	Koppers shareholders’ equity		148.6			147.5			797.8			280.7			(1,226.0	)		148.6
	Noncontrolling interests		0			0			0			16.4			0			16.4
	Total liabilities and equity	$	153.4		$	1,235.50		$	875.7		$	574		$	(1,484.7	)	$	1,353.90
	Condensed Consolidating Balance Sheet
	December 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	29.9		$	0.1		$	52.2		$	0		$	82.2
	Receivables, net		0			75.6			9.3			82			0			166.9
	Affiliated receivables		0.2			1.1			3.9			2.3			(7.5	)		0
	Inventories, net		0			86.1			0			82.9			(0.2	)		168.8
	Deferred tax assets		0			7.9			1.5			0.6			0			10
	Other current assets		0			7.3			0.6			37.3			0			45.2
	Total current assets		0.2			207.9			15.4			257.3			(7.7	)		473.1
	Equity investments		174.7			333.5			182.9			4.6			(689.1	)		6.6
	Property, plant and equipment, net		0			112.2			0			84.8			0			197
	Goodwill		0			39.8			0			32.9			0			72.7
	Intangible assets, net		0			3.3			0			8.9			0			12.2
	Deferred tax assets		0			2.4			(1.4	)		8.3			0			9.3
	Affiliated loan receivables		0			8.5			123.8			40.9			(173.2	)		0
	Other noncurrent assets		0			11.7			0			2.3			0			14
	Total assets	$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
	LIABILITIES AND EQUITY
	Accounts payable	$	0		$	48.3		$	6.7		$	52.6		$	0		$	107.6
	Affiliated payables		0			1.9			4			8.6			(14.5	)		0
	Accrued liabilities		5.1			27.8			0.5			54.1			0			87.5
	Total current liabilities		5.1			78			11.2			115.3			(14.5	)		195.1
	Long-term debt		0			296.5			0			6.6			0			303.1
Affiliated debt		0			109.5			8.5			55.2			(173.2	)		0
Other long-term liabilities		0			67.6			2.5			26.8			0			96.9
Total liabilities		5.1			551.6			22.2			203.9			(187.7	)		595.1
Koppers shareholders’ equity		169.8			167.7			298.5			216.1			(682.3	)		169.8
Noncontrolling interests		0			0			0			20			0			20
Total liabilities and equity	$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
Condensed Consolidating Statement of Cash Flows	'
	Condensed Consolidating Statement of Cash Flows
	For the Nine Months Ended September 30, 2014
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	16.5		$	(0.9	)	$	26.4		$	-4.5		$	(26.7	)	$	10.8
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(508.0	)		(15.1	)		(47.2	)		14.8			(555.5	)
	(Loans to) repayments from affiliates		0			(24.4	)		(33.9	)		(0.5	)		58.8			0
	Net cash proceeds (payments) from divestitures and asset sales		0			0.1			0			0			0			0.1
	Net cash provided by (used in) investing activities		0			(532.3	)		(49.0	)		(47.7	)		73.6			(555.4	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of long-term debt		0			514.9			0			48.9			0			563.8
	Borrowings (repayments) of affiliated debt		0			17.5			24.3			17			(58.8	)		0
	Deferred financing costs		0			(11.1	)		0			0			0			(11.1	)
	Other financing activities		0			0			0			1.4			0			1.4
	Dividends paid		(15.2	)		(17.8	)		0			(8.9	)		26.7			(15.2	)
	Stock issued (repurchased)		(1.3	)		0			0			14.8			(14.8	)		(1.3	)
	Net cash provided by (used in) financing activities		(16.5	)		503.5			24.3			73.2			(46.9	)		537.6
	Effect of exchange rates on cash		0			0			0			(0.1	)		0			(0.1	)
	Net increase (decrease) in cash and cash equivalents		0			(29.7	)		1.7			20.9			0			(7.1	)
	Cash and cash equivalents at beginning of year		0			29.9			0.1			52.2			0			82.2
	Cash and cash equivalents at end of period	$	0		$	0.2		$	1.8		$	73.1		$	0		$	75.1
	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		$	43.7		$	2.5		$	23.1		$	(36.3	)	$	65.6
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(13.3	)		0			(16.1	)		0			(29.4	)
	(Loans to) repayments from affiliates		0			(3.0	)		(5.5	)		(3.2	)		11.7			0
	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			(14.9	)		(5.5	)		(18.3	)		11.7			(27.0	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of affiliated debt		0			8.7			3			0			(11.7	)		0
	Deferred financing costs		0			(1.2	)		0			0			0			(1.2	)
	Other financing activities		0			0			0			2.3			0			2.3
	Dividends paid		(15.3	)		(33.2	)		0			(3.1	)		36.3			(15.3	)
	Stock issued (repurchased)		(17.3	)		0			0			0			0			(17.3	)
	Net cash provided by (used in) financing activities		(32.6	)		(25.7	)		3			(0.8	)		24.6			(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

Subsidiary_Guarantor_Informati3

Subsidiary Guarantor Information for Shelf Registration (Tables)	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Condensed Consolidating Statement of Comprehensive Income	'
	Condensed Consolidating Statement of Comprehensive Income
	For the Three Months Ended September 30, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	220.5		$	17.1		$	103		$	121.7		$	(22.2	)	$	440.1
	Cost of sales including depreciation and amortization		0			194.8			13.6			91			113.4			(22.0	)		390.8
	Selling, general and administrative		0.3			16.8			0.2			5.2			9.5			0			32
	Operating profit (loss)		(0.3	)		8.9			3.3			6.8			(1.2	)		(0.2	)		17.3
	Other income (expense)		0			0			1.2			0			(0.3	)		(1.1	)		(0.2	)
	Equity income of subsidiaries		(2.6	)		6.5			(0.4	)		(4.1	)		(0.1	)		0.7			0
	Interest expense (income)		0			11.4			0			1			0.6			(1.1	)		11.9
	Income taxes		(0.2	)		6.6			0.2			2.5			0.4			0			9.5
	Income from continuing operations		(2.7	)		(2.6	)		3.9			(0.8	)		(2.6	)		0.5			(4.3	)
	Discontinued operations		0			0			0			0			0.1			0			0.1
	Noncontrolling interests		0			0			0			0			(1.5	)		0			(1.5	)
	Net income attributable to Koppers	$	(2.7	)	$	(2.6	)	$	3.9		$	(0.8	)	$	(1.0	)	$	0.5		$	(2.7	)
	Comprehensive income attributable to Koppers	$	(18.6	)	$	(18.4	)	$	(12.4	)	$	(10.4	)	$	(5.9	)	$	47.1		$	(18.6	)
	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		$	120.8		$	43.3		$	(10.9	)	$	395.2
	Cost of sales including depreciation and amortization		0			197.5			7.2			103.7			40.4			(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)		0			0.4			1			0.7			0.1			(0.9	)		1.3
	Equity income of subsidiaries		19.4			14.2			8.2			0.4			0.1			(42.3	)		0
	Interest expense (income)		0			6.8			0			0.7			0			(0.8	)		6.7
	Income taxes		(0.2	)		10.2			0			3.8			0.3			0			14.1
	Income from continuing operations		19.1			19.4			13.8			8.2			1.4			(42.3	)		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		$	19.4		$	13.8		$	8.1		$	1		$	(42.3	)	$	19.1
	Comprehensive income attributable to Koppers	$	25.8		$	26		$	14.5		$	13.7		$	2.9		$	(57.1	)	$	25.8
	Condensed Consolidating Statement of Comprehensive Income
	For the Nine Months Ended September 30, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	600.5		$	35		$	321.1		$	215.3		$	(43.6	)	$	1,128.30
	Cost of sales including depreciation and amortization		0			539.7			22.8			291.7			211.3			(43.6	)		1,021.90
	Selling, general and administrative		1.3			44.6			0.8			16.4			12.2			0			75.3
	Operating profit (loss)		(1.3	)		16.2			11.4			13			(8.2	)		0			31.1
	Other income (expense)		0			0.1			3			0.1			(0.3	)		(3.2	)		(0.3	)
	Equity income of subsidiaries		1.9			16.1			(7.4	)		(9.2	)		0			(1.4	)		0
	Interest expense (income)		0			24.7			0			2.4			1.4			(3.2	)		25.3
	Income taxes		(0.5	)		5.8			(5.7	)		8.9			0.6			0			9.1
	Income from continuing operations		1.1			1.9			12.7			(7.4	)		(10.5	)		(1.4	)		(3.6	)
	Discontinued operations		0			0			0			0			0			0			0
	Noncontrolling interests		0			0			0			0			(4.7	)		0			(4.7	)
	Net income attributable to Koppers	$	1.1		$	1.9		$	12.7		$	(7.4	)	$	(5.8	)	$	(1.4	)	$	1.1
	Comprehensive income attributable to Koppers	$	(9.2	)	$	(8.3	)	$	1.1		$	(14.4	)	$	(6.5	)	$	28.1		$	(9.2	)
	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		$	348.7		$	123.8		$	(44.8	)	$	1,136.50
Cost of sales including depreciation and amortization		0			580.6			34.3			305.8			116			(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)		0			1.3			3.1			0.8			0.7			(3.1	)		2.8
Equity income of subsidiaries		45.4			35.7			18.3			1.4			0.1			(100.9	)		0
Interest expense (income)		0			20.3			0			2.5			0.5			(3.1	)		20.2
Income taxes		(0.6	)		21.3			0.2			7.4			1			0			29.3
Income from continuing operations		44.5			45.4			34.7			18.4			3.6			(100.8	)		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		$	45.4		$	34.7		$	18.3		$	2.4		$	(100.8	)	$	44.5
Comprehensive income attributable to Koppers	$	40.8		$	41.6		$	22.8		$	15.8		$	2.9		$	(83.1	)	$	40.8
Condensed Consolidating Balance Sheet	'
	Condensed Consolidating Balance Sheet
	September 30, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0			$0.20			$0.10			$31.90			$42.90			$0.00			$75.10
	Receivables, net		0			91.3			10.7			43.1			90.8			0			235.9
	Affiliated Receivables		0.1			4.1			(2.8	)		6.4			12.9			(20.7	)		0
	Inventories, net		0			87.8			0			66.9			73.2			(0.2	)		227.7
	Deferred tax assets		0			7.9			3.9			0			8.4			0			20.2
	Other current assets		0			5.5			0.4			12.7			30.5			0			49.1
	Total current assets		0.1			196.8			12.3			161			258.7			(20.9	)		608
	Equity investments		153.3			832.1			175.5			44.9			3.8			(1,203.9	)		5.7
	Property, plant and equipment, net		0			111.9			0.9			40			134			0			286.8
	Goodwill		0			39.8			0			30.7			167.5			0			238
	Intangible assets, net		0			2.4			0			8.3			169.4			0			180.1
	Deferred tax assets		0			0.5			2.3			5.1			2.4			0			10.3
	Affiliated loan receivables		0			32.6			155.9			0.1			41.4			(230.0	)		0
	Other noncurrent assets		0			19.4			0			0.8			4.7			0.1			25
	Total assets	$	153.4		$	1,235.50		$	346.9		$	290.9		$	781.9		$	(1,454.7	)	$	1,353.90
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	52.2		$	0		$	28		$	42.1		$	0		$	122.4
	Affiliated payables		0			14			6.3			2.5			3.7			(26.5	)		0
	Accrued liabilities		4.7			33.8			0.4			29			39.8			0			107.7
	Short-term debt and current portion of long-term debt		0			30			0			0			0			0			30
	Total current liabilities		4.8			130			6.7			59.5			85.6			(26.5	)		260.1
	Long-term debt		0			781.8			0			0			55.7			0			837.5
	Affiliated debt		0			121			32.6			54.7			21.7			(230.0	)		0
	Other long-term liabilities		0			55.2			2.5			17.7			15.8			0.1			91.3
	Total liabilities		4.8			1,088.00			41.8			131.9			178.8			(256.4	)		1,188.90
	Koppers shareholders’ equity		148.6			147.5			305.1			159			586.7			(1,198.3	)		148.6
	Noncontrolling interests		0			0			0			0			16.4			0			16.4
	Total liabilities and equity	$	153.4		$	1,235.50		$	346.9		$	290.9		$	781.9		$	(1,454.7	)	$	1,353.90
	Condensed Consolidating Balance Sheet
	December 31, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	29.9		$	0.1		$	43.5		$	8.7		$	0		$	82.2
	Receivables, net		0			75.6			9.3			55.5			26.5			0			166.9
	Affiliated receivables		0.2			1.1			3.9			0.8			1.6			(7.6	)		0
	Inventories, net		0			86.1			0			75.2			7.7			(0.2	)		168.8
	Deferred tax assets		0			7.9			1.5			0			0.6			0			10
	Other current assets		0			7.3			0.6			17.5			19.8			0			45.2
	Total current assets		0.2			207.9			15.4			192.5			64.9			(7.8	)		473.1
	Equity investments		174.7			333.5			182.9			50.5			4.5			(739.5	)		6.6
	Property, plant and equipment, net		0			112.2			0			38.1			46.7			0			197
	Goodwill		0			39.8			0			31.5			1.4			0			72.7
	Intangible assets, net		0			3.3			0			8.9			0			0			12.2
	Deferred tax assets		0			2.4			(1.4	)		5.5			2.8			0			9.3
	Affiliated loan receivables		0			8.5			123.8			0.1			40.8			(173.2	)		0
	Other noncurrent assets		0			11.7			0			1			1.3			0			14
	Total assets	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
	LIABILITIES AND EQUITY
	Accounts payable	$	0		$	48.3		$	6.7		$	40.6		$	12		$	0		$	107.6
	Affiliated payables		0			1.9			4			0.4			8.4			(14.7	)		0
	Accrued liabilities		5.1			27.8			0.5			31.4			22.7			0			87.5
	Total current liabilities		5.1			78			11.2			72.4			43.1			(14.7	)		195.1
	Long-term debt		0			296.5			0			0			6.6			0			303.1
Affiliated debt		0			109.5			8.5			55.2			0			(173.2	)		0
Other long-term liabilities		0			67.6			2.5			19.6			7.2			0			96.9
Total liabilities		5.1			551.6			22.2			147.2			56.9			(187.9	)		595.1
Koppers shareholders’ equity		169.8			167.7			298.5			180.9			85.5			(732.6	)		169.8
Noncontrolling interests		0			0			0			0			20			0			20
Total liabilities and equity	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
Condensed Consolidating Statement of Cash Flows	'
	Condensed Consolidating Statement of Cash Flows
	For the Nine Months Ended September 30, 2014
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	16.5		$	(0.9	)	$	19.1		$	11.4		$	-8.6		$	(26.7	)	$	10.8
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(508.0	)		(15.7	)		(14.1	)		(36.6	)		18.9			(555.5	)
	(Loans to) repayments from affiliates		0			(24.4	)		(27.7	)		0			(6.7	)		58.8			0
	Net cash proceeds (payments) from divestitures and asset sales		0			0.1			0			0			0			0			0.1
	Net cash provided by (used in) investing activities		0			(532.3	)		(43.4	)		(14.1	)		(43.3	)		77.7			(555.4	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of long-term debt		0			514.9			0			0			48.9			0			563.8
	Borrowings (repayments) of affiliated debt		0			17.5			24.3			0			17			(58.8	)		0
	Deferred financing costs		0			(11.1	)		0			0			0			0			(11.1	)
	Other financing activities		0			0			0			0			1.4			0			1.4
	Dividends paid		(15.2	)		(17.8	)		0			(8.9	)		0			26.7			(15.2	)
	Stock issued (repurchased)		(1.3	)		0			0			0			18.9			(18.9	)		(1.3	)
	Net cash provided by (used in) financing activities		(16.5	)		503.5			24.3			(8.9	)		86.2			(51.0	)		537.6
	Effect of exchange rates on cash		0			0			0			0			(0.1	)		0			(0.1	)
	Net increase (decrease) in cash and cash equivalents		0			(29.7	)		0			(11.6	)		34.2			0			(7.1	)
	Cash and cash equivalents at beginning of year		0			29.9			0.1			43.5			8.7			0			82.2
	Cash and cash equivalents at end of period	$	0		$	0.2		$	0.1		$	31.9		$	42.9		$	0		$	75.1
	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		$	43.7		$	2.5		$	25.8		$	(2.7	)	$	(36.3	)	$	65.6
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(13.3	)		0			(14.3	)		(9.5	)		7.7			(29.4	)
	(Loans to) repayments from affiliates		0			(3.0	)		(5.5	)		0			(3.2	)		11.7			0
	Net cash proceeds (payments) from divestitures and asset sales		0			1.4			0			1			0			0			2.4
	Net cash provided by (used in) investing activities		0			(14.9	)		(5.5	)		(13.3	)		(12.7	)		19.4			(27.0	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of affiliated debt		0			8.7			3			0			0			(11.7	)		0
	Deferred financing costs		0			(1.2	)		0			0			0			0			(1.2	)
	Other financing activities		0			0			0			0			2.3			0			2.3
	Dividends paid		(15.3	)		(33.2	)		0			(3.1	)		0			36.3			(15.3	)
	Stock issued (repurchased)		(17.3	)		0			0			0			7.7			(7.7	)		(17.3	)
	Net cash provided by (used in) financing activities		(32.6	)		(25.7	)		3			(3.1	)		10			16.9			(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

Dividends_Additional_Informati

Dividends - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Nov. 05, 2014
					Subsequent Event [Member]
Dividends Payable [Line Items]	'	'	'	'	'
Dividends declared per common share	$0.25	$0.25	$0.75	$0.75	$0.25
Common share, dividend payable date	'	'	5-Jan-15	'	'
Common share, dividend declared date	'	'	5-Nov-14	'	'
Common share, dividend record date	'	'	17-Nov-14	'	'

Plant_Closures_and_Discontinue2

Plant Closures and Discontinued Operations - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2013
Restructuring Cost and Reserve [Line Items]	'	'	'
Costs related to closure	'	$13.10	'
Impairment charges	6.9	4.7	0
Carbon Materials and Chemicals [Member]	'	'	'
Restructuring Cost and Reserve [Line Items]	'	'	'
Impairment charges	'	$4.70	'
Carbon Materials and Chemicals [Member] | Discontinued Operations [Member]	'	'	'
Restructuring Cost and Reserve [Line Items]	'	'	'
Future completion period, closure	'	'2015	'

Plant_Closures_and_Discontinue3

Plant Closures and Discontinued Operations - Summary of Restructuring Activities and Related Reserves (Detail) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	$9	$13.30
Accrual	13.1	'
Reversal of accrued charges	'	-0.4
Cash paid	-9.5	-2.2
Currency translation	-0.4	-1.7
Reserve, Ending Balance	12.2	9
Severance and Employee Benefits [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	0.1	0.2
Accrual	10	'
Reversal of accrued charges	'	-0.1
Cash paid	-9.3	0
Currency translation	-0.2	0
Reserve, Ending Balance	0.6	0.1
Environmental Remediation [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	5.6	6.7
Accrual	0	'
Reversal of accrued charges	'	0
Cash paid	0	-0.1
Currency translation	-0.1	-1
Reserve, Ending Balance	5.5	5.6
Site Demolition [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	3.3	6.3
Accrual	3.1	'
Reversal of accrued charges	'	-0.3
Cash paid	-0.2	-2
Currency translation	-0.1	-0.7
Reserve, Ending Balance	6.1	3.3
Other [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	0	0.1
Accrual	0	'
Reversal of accrued charges	'	0
Cash paid	0	-0.1
Currency translation	0	0
Reserve, Ending Balance	$0	$0

Business_Acquisitions_Addition

Business Acquisitions - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

0 Months Ended

0 Months Ended

0 Months Ended

3 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Jan. 20, 2014

Jan. 20, 2014

Jan. 20, 2014

Jan. 20, 2014

Sep. 30, 2014

Jan. 20, 2014

Sep. 30, 2014

Aug. 15, 2014

Sep. 30, 2014

Dec. 31, 2013

Aug. 15, 2014

Aug. 15, 2014

Tolko Industries Ltd [Member]

Tolko Industries Ltd [Member]

Tolko Industries Ltd [Member]

Tolko Industries Ltd [Member]

Tolko Industries Ltd [Member]

Tolko Industries Ltd [Member]

Tolko Industries Ltd [Member]

Osmose Holdings, Inc. [Member]

Osmose Holdings, Inc. [Member]

Osmose Holdings, Inc. [Member]

Osmose Holdings, Inc. [Member]

Osmose Holdings, Inc. [Member]

Customer Relationships [Member]

Customer Relationships [Member]

Railroad and Utility Products and Services [Member]

Railroad and Utility Products and Services [Member]

Performance Chemicals [Member]

Senior Secured Credit Facilities [Member]

Term Loan Facility [Member]

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Business acquisition purchase price

'

'

'

'

'

$29.80

'

'

'

'

'

'

'

'

'

'

'

Acquired assets consisted of inventory

'

'

'

'

'

'

16

'

'

'

'

'

'

51.9

'

'

'

Acquired assets consisted of plant and equipment

'

'

'

'

'

'

3.6

'

'

'

'

'

'

59.6

'

'

'

Intangible assets consisting primarily of customer relationships

'

'

'

'

'

'

'

'

7.4

'

'

'

'

'

'

'

'

Goodwill

238

'

238

'

72.7

'

'

'

'

6.8

1.8

158

'

'

'

'

'

Customer contracts amortization period

'

'

'

'

'

'

'

'12 years

'

'

'

'

'

'

'

'

'

Business acquisition purchase price

'

'

'

'

'

'

'

'

'

'

'

'

494.1

'

'

'

'

Payments to acquire businesses, net of cash acquired

'

'

496.5

0

'

'

'

'

'

'

'

'

27.2

'

'

'

'

Amount available under credit facility

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

500

300

Business acquisition, revenues

'

'

'

'

'

'

'

'

'

'

'

'

'

'

391.5

'

'

Business acquisition, net income from continuing operations

-2.8

19.2

1.1

44.6

'

'

'

'

'

'

'

'

'

'

19.3

'

'

Business acquisition, total revenue

$440.10

$395.20

$1,128.30

$1,136.50

'

'

'

'

'

'

'

'

'

$53.40

'

'

'

Business_Acquisitions_Schedule

Business Acquisitions - Schedule of Company's Preliminary Fair Value Estimates for Osmose Entities (Detail) (Osmose Holdings, Inc. [Member], USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Osmose Holdings, Inc. [Member]	'
Loans At Acquisition Date [Line Items]	'
Cash and cash equivalents	$27.20
Accounts receivable, net	60
Inventories, net	51.9
Other current assets	9.5
Property, plant and equipment	59.6
Goodwill	164.8
Intangible assets	164.2
Other assets	4
Total assets acquired	541.2
Accounts payable	21.2
Accrued liabilities	17.4
Other liabilities	8.5
Total liabilities assumed	47.1
Net assets acquired	$494.10

Business_Acquisitions_Summary_

Business Acquisitions - Summary of Company's Revenue And Net Income From Continuing Operations (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Business Combination Increase Decrease To Reflect Liabilities Acquired At Fair Value [Abstract]	'	'	'	'
Revenue	$500.10	$498.40	$1,392.90	$1,433
Income from continuing operations attributable to Koppers	$3.40	$23.20	$16.40	$45.10

Fair_Value_Measurements_Schedu

Fair Value Measurements - Schedule of Company's Financial Instruments (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Fair Value [Member]	'	'
Financial assets:	'	'
Cash and cash equivalents, including restricted cash	$75.10	$82.20
Investments and other assets	1.4	1.4
Financial liabilities:	'	'
Long-term debt (including current portion)	883.7	331.2
Carrying Value [Member]	'	'
Financial assets:	'	'
Cash and cash equivalents, including restricted cash	75.1	82.2
Investments and other assets	1.4	1.4
Financial liabilities:	'	'
Long-term debt (including current portion)	$867.50	$303.10

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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Equity [Abstract]	'	'	'	'
Net (loss) income	($4.20)	$19.50	($3.60)	$45.70
Other comprehensive (loss) income :	'	'	'	'
Change in currency translation adjustment	-10.6	5.6	-9.8	-0.4
Change in foreign currency transactions of long-term subsidiary investments	-3.8	0.3	-0.5	-6.6
Change in derivative financial instrument net loss, net of tax benefit of $(0.8), $0.0, $(0.8) and $0.0	-1.9	0	-1.9	0
Change in unrecognized pension net loss, net of tax expense of $0.2, $0.8, $0.7 and $2.3	0.6	1.2	1.8	3.5
Change in unrecognized prior service cost, net of tax expense of $0.0, $0.0, $0.0 and $0.0	0	0	-0.1	0.1
Total comprehensive (loss) income	-19.9	26.6	-14.1	42.3
Less: comprehensive (loss) income attributable to noncontrolling interests	-1.3	0.8	-4.9	1.5
Comprehensive (loss) income attributable to Koppers	($18.60)	$25.80	($9.20)	$40.80

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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Equity [Abstract]	'	'	'	'
Tax benefit, derivative financial instrument	$0.80	$0	$0.80	$0
Tax expense, unrecognized pension net loss	0.2	0.8	0.7	2.3
Tax expense, unrecognized prior service cost	$0	$0	$0	$0

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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Comprehensive Income And Equity [Line Items]	'	'	'	'
Balance	'	'	$189.80	$168.10
Net income (loss)	-4.2	19.5	-3.6	45.7
Issuance of common stock	'	'	0.7	0.2
Employee stock plans	'	'	4.9	5.2
Other comprehensive income (loss)	'	'	-10.5	-3.4
Dividends	'	'	-15.6	-15.9
Investment in noncontrolling interests	'	'	1.3	2.3
Repurchases of common stock	'	'	-2	-17.5
Balance	165	184.7	165	184.7
Total Koppers Shareholders' Equity [Member]	'	'	'	'
Comprehensive Income And Equity [Line Items]	'	'	'	'
Balance	'	'	169.8	150.6
Net income (loss)	'	'	1.1	44.5
Issuance of common stock	'	'	0.7	0.2
Employee stock plans	'	'	4.9	5.2
Other comprehensive income (loss)	'	'	-10.3	-3.7
Dividends	'	'	-15.6	-15.9
Investment in noncontrolling interests	'	'	0	0
Repurchases of common stock	'	'	-2	-17.5
Balance	148.6	163.4	148.6	163.4
Noncontrolling Interests [Member]	'	'	'	'
Comprehensive Income And Equity [Line Items]	'	'	'	'
Balance	'	'	20	17.5
Net income (loss)	'	'	-4.7	1.2
Issuance of common stock	'	'	0	0
Employee stock plans	'	'	0	0
Other comprehensive income (loss)	'	'	-0.2	0.3
Dividends	'	'	0	0
Investment in noncontrolling interests	'	'	1.3	2.3
Repurchases of common stock	'	'	0	0
Balance	$16.40	$21.30	$16.40	$21.30

Earnings_per_Common_Share_Sche

Earnings per Common Share - Schedule of Computation 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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]	'	'	'	'
Net (loss) income attributable to Koppers	($2.70)	$19.10	$1.10	$44.50
Less: income (loss) from discontinued operations	0.1	-0.1	0	-0.1
(Loss) Income from continuing operations attributable to Koppers	($2.80)	$19.20	$1.10	$44.60
Weighted average common shares outstanding:	'	'	'	'
Basic	20,495	20,577	20,452	20,657
Effect of dilutive securities	108	224	141	230
Diluted	20,603	20,801	20,593	20,887
(Loss) earnings per common share - continuing operations:	'	'	'	'
Basic (loss) earnings per common share	($0.14)	$0.93	$0.05	$2.16
Diluted (loss) earnings per common share	($0.14)	$0.92	$0.05	$2.13
Other data:	'	'	'	'
Antidilutive securities excluded from computation of diluted earnings per common share	265	254	260	236

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, 2014	Dec. 31, 2011
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Future compensation expense related to non-vested stock-based compensation arrangements	7.4	'
Future compensation expense, weighted-average expected period of recognition in months	'23 months	'
Performance Stock Units [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, vesting period in years	'3 years	'
Performance stock unit granted in years	'3 years	'2 years
Number of vest performance stock unit, if performance criteria are not achieved	0	'
Performance Stock Units [Member] | 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%	'
Performance Stock Units [Member] | 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 (RSUs) [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, vesting period in years	'3 years	'
Restricted Stock Units (RSUs) [Member] | Board of Directors [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, vesting period in years	'1 year	'
Employee Stock Option [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, term in years	'10 years	'

Stockbased_Compensation_Summar

Stock-based Compensation - Summary of Performance Stock Units (Detail)	Sep. 30, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	458,299	468,820
Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	280,380	319,984
Minimum Shares [Member] | 2012 - 2014 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	0	'
Minimum Shares [Member] | 2013 - 2015 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	0	'
Minimum Shares [Member] | 2014 - 2016 [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	87,059	'
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	85,207	'
Target Shares [Member] | 2014 - 2016 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	102,149	'
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	130,559	'
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	127,811	'
Maximum Shares [Member] | 2014 - 2016 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	153,224	'

Stockbased_Compensation_Summar1

Stock-based Compensation - Summary of Status and Activity of Non-Vested Stock Awards (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	468,820
Granted	203,573
Credited from dividends	12,238
Vested	-189,419
Forfeited	-36,913
Non-vested, Ending Balance	458,299
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit	$40.30
Granted, Weighted Average Grant Date Fair Value per Unit	$37.90
Credited from dividends, Weighted Average Grant Date Fair Value per Unit	$38.52
Vested, Weighted Average Grant Date Fair Value per Unit	$40.18
Forfeited, Weighted Average Grant Date Fair Value per Unit	$39.51
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit	$39.30
Restricted Stock Units (RSUs) [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	148,836
Granted	95,067
Credited from dividends	3,813
Vested	-57,102
Forfeited	-12,695
Non-vested, Ending Balance	177,919
Performance Stock Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	319,984
Granted	108,506
Credited from dividends	8,425
Vested	-132,317
Forfeited	-24,218
Non-vested, Ending Balance	280,380

Stockbased_Compensation_Stock_

Stock-based Compensation - Stock Options Fair Value Assumptions (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014
February 2014 Grant [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Grant date price per share of option award	$37.93
Expected dividend yield per share	2.75%
Expected life in years	'6 years 6 months
Expected volatility	52.14%
Risk-free interest rate	1.98%
Grant date fair value per share of option awards	$15.26
February 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

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, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Options, Outstanding at December 31, 2013	421,080
Options, Granted	106,658
Options, Exercised	-26,349
Options, Expired	-6,019
Options, Forfeited	-34,707
Options, Outstanding at September 30, 2014	460,663
Options, Exercisable at September 30, 2014	202,863
Weighted Average Exercise Price per Option, Outstanding at December 31, 2013	$35.96
Weighted Average Exercise Price per Option, Granted	$37.93
Weighted Average Exercise Price per Option, Exercised	$25.51
Weighted Average Exercise Price per Option, Expired	$40.15
Weighted Average Exercise Price per Option, Forfeited	$39.75
Weighted Average Exercise Price per Option, Outstanding at September 30, 2014	$36.67
Weighted Average Exercise Price per Option, Exercisable at September 30, 2014	$33
Weighted Average Remaining Contractual Term, Outstanding at September 30, 2014	'6 years 9 months 29 days
Weighted Average Remaining Contractual Term, Exercisable at September 30, 2014	'4 years 8 months 16 days
Aggregate Intrinsic Value, Outstanding at September 30, 2014	$0.70
Aggregate Intrinsic Value, Exercisable at September 30, 2014	$0.70

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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Stock-based compensation expense recognized:	'	'	'	'
Selling, general and administrative expenses	$1.40	$1.90	$4.60	$4.70
Less related income tax benefit	0.6	0.8	1.8	1.9
Decrease in net income attributable to Koppers	$0.80	$1.10	$2.80	$2.80

Segment_Information_Additional

Segment Information - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2014
	Segment
Segment Reporting [Abstract]	'
Number of reportable segments	3

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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues from external customers:	'	'	'	'
Revenues from external customers	$440.10	$395.20	$1,128.30	$1,136.50
Intersegment revenues:	'	'	'	'
Intersegment revenues	440.1	395.2	1,128.30	1,136.50
Depreciation and amortization expense (a):	'	'	'	'
Depreciation and amortization expense	11.2	7.2	29.8	21.8
Operating profit:	'	'	'	'
Operating profit (loss)	17.3	39.1	31.1	92.5
Operating Segments [Member] | Carbon Materials and Chemicals [Member]	'	'	'	'
Revenues from external customers:	'	'	'	'
Revenues from external customers	226.6	241.6	637.8	692.4
Intersegment revenues:	'	'	'	'
Intersegment revenues	226.6	241.6	637.8	692.4
Depreciation and amortization expense (a):	'	'	'	'
Depreciation and amortization expense	6.6	4.5	18.7	13.5
Operating profit:	'	'	'	'
Operating profit (loss)	5.2	21.8	0.2	47.4
Operating Segments [Member] | Railroad and Utility Products and Services [Member]	'	'	'	'
Revenues from external customers:	'	'	'	'
Revenues from external customers	167.4	153.6	444.4	444.1
Intersegment revenues:	'	'	'	'
Intersegment revenues	167.4	153.6	444.4	444.1
Depreciation and amortization expense (a):	'	'	'	'
Depreciation and amortization expense	2.2	2.7	8.7	8.3
Operating profit:	'	'	'	'
Operating profit (loss)	17.4	17.8	41.3	46.6
Operating Segments [Member] | Performance Chemicals [Member]	'	'	'	'
Revenues from external customers:	'	'	'	'
Revenues from external customers	46.1	0	46.1	0
Intersegment revenues:	'	'	'	'
Intersegment revenues	46.1	0	46.1	0
Depreciation and amortization expense (a):	'	'	'	'
Depreciation and amortization expense	2.4	0	2.4	0
Operating profit:	'	'	'	'
Operating profit (loss)	1.3	0	1.3	0
Intersegment [Member]	'	'	'	'
Revenues from external customers:	'	'	'	'
Revenues from external customers	21.5	23.3	62.8	70.9
Intersegment revenues:	'	'	'	'
Intersegment revenues	21.5	23.3	62.8	70.9
Intersegment [Member] | Carbon Materials and Chemicals [Member]	'	'	'	'
Revenues from external customers:	'	'	'	'
Revenues from external customers	20.7	23.3	62	70.9
Intersegment revenues:	'	'	'	'
Intersegment revenues	20.7	23.3	62	70.9
Intersegment [Member] | Performance Chemicals [Member]	'	'	'	'
Revenues from external customers:	'	'	'	'
Revenues from external customers	0.8	0	0.8	0
Intersegment revenues:	'	'	'	'
Intersegment revenues	0.8	0	0.8	0
Corporate, Non-Segment [Member]	'	'	'	'
Operating profit:	'	'	'	'
Operating profit (loss)	($6.60)	($0.50)	($11.70)	($1.50)

Segment_Information_Summary_of1

Segment Information - Summary of Results of Segment Operations (Parenthetical) (Detail) (USD $)	3 Months Ended	9 Months Ended			3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014
				Carbon Materials and Chemicals [Member]	Netherlands [Member]	Netherlands [Member]	China [Member]
Revenue from External Customer [Line Items]	'	'	'	'	'	'	'
Impairment charges	$6.90	$4.70	$0	$4.70	'	'	$4.70
Plant closure cost	'	'	'	'	$2.60	$13.40	'

Segment_Information_Summary_of2

Segment Information - Summary of Tangible and Intangible Assets by Segments (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Segment assets:	'	'
Segment assets	$1,353.90	$784.90
Goodwill:	'	'
Goodwill	238	72.7
Operating Segments [Member]	'	'
Segment assets:	'	'
Segment assets	1,353.90	784.9
Goodwill:	'	'
Goodwill	238	72.7
Carbon Materials and Chemicals [Member] | Operating Segments [Member]	'	'
Segment assets:	'	'
Segment assets	537.2	535.5
Goodwill:	'	'
Goodwill	67.2	68
Railroad and Utility Products and Services [Member] | Operating Segments [Member]	'	'
Segment assets:	'	'
Segment assets	293.8	179.3
Goodwill:	'	'
Goodwill	12.8	4.7
Performance Chemicals [Member] | Operating Segments [Member]	'	'
Segment assets:	'	'
Segment assets	474.3	0
Goodwill:	'	'
Goodwill	158	0
All Other [Member] | Operating Segments [Member]	'	'
Segment assets:	'	'
Segment assets	$48.60	$70.10

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'	'	'	'	'
Percentage of pretax income	94.20%	46.40%	80.90%	43.00%	'
Net tax benefit included in income taxes, discrete items	$0.30	$1.60	$6	$3	'
U.S. federal statutory rate	35.00%	35.00%	35.00%	35.00%	'
Taxes on foreign earnings	47.70%	10.20%	38.80%	6.60%	'
State taxes	0.10%	1.80%	0.80%	1.80%	'
Uncertain tax positions	2.70%	0.90%	2.00%	0.80%	'
Nondeductible expenses	11.00%	0.50%	6.70%	0.50%	'
Domestic manufacturing deduction	-1.80%	-1.80%	-2.00%	-1.70%	'
Tax credits	-0.50%	-0.20%	-0.40%	'	'
Unrecognized tax benefits with impact on the effective tax rate	4.5	'	4.5	'	4.5
Unrecognized tax benefits	5.8	'	5.8	'	6.1
Accrued interest expense and penalties	$1.40	'	$1.40	'	$1.20

Inventories_Components_of_Inve

Inventories - Components of Inventories (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Inventory Disclosure [Abstract]	'	'
Raw materials	$151.10	$105.40
Work in process	19.7	19.2
Finished goods	111.9	94.8
Inventories, gross	282.7	219.4
Less revaluation to LIFO	55	50.6
Net	$227.70	$168.80

Property_Plant_and_Equipment_P

Property, Plant and Equipment - Property, Plant and Equipment (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	$741.20	$647.80
Less accumulated depreciation	454.4	450.8
Net	286.8	197
Land [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	19.4	9.1
Buildings [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	45	30.6
Machinery and Equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	$676.80	$608.10

Property_Plant_and_Equipment_A

Property, Plant and Equipment - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended			12 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Oct. 31, 2013	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014
	Battery				Koppers Carbon and Chemical Company Limited [Member]	Koppers Carbon and Chemical Company Limited [Member]	China [Member]
Property, Plant and Equipment [Line Items]	'	'	'	'	'	'	'
Impairment charges	'	$6.90	$4.70	$0	'	'	$4.70
Assets impairment charges net of non controlling interest	'	'	2.8	'	'	'	'
Percentage of operations in Tangshan, China of owned subsidiary	'	'	'	'	60.00%	'	60.00%
Number of coke batteries to be closed	2	'	'	'	'	'	'
Number of coke batteries closed	1	'	'	'	'	'	'
Profit after deduction of profit attributable to non-controlling interests	'	'	'	'	'	$3.30	'
Supply of export commitments	'	'	30.00%	'	'	'	'

Pensions_and_Postretirement_Be2

Pensions and Postretirement Benefit Plans - Additional Information (Detail)	Sep. 30, 2014
	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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Postemployment Benefits [Abstract]	'	'	'	'
Service cost	$0.70	$0.90	$1.90	$2.60
Interest cost	2.8	2.7	8.8	8
Expected return on plan assets	-3.5	-3.2	-10.5	-9.5
Amortization of prior service cost	0	0	-0.1	0.1
Amortization of net loss	1	1.9	3	5.7
Net periodic benefit cost	1	2.3	3.1	6.9
Defined contribution plan expense	1.3	1.2	4.5	4.1
Other postretirement benefit plans	0.1	0.1	0.3	0.3
Multi-employer pension plan expense	$0	$0.10	$0.20	$0.40

Debt_Schedule_of_LongTerm_Debt

Debt - Schedule of Long-Term Debt Instruments (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]	'	'
Senior Notes	$296.90	$296.50
Total debt	867.5	303.1
Less short term debt and current maturities of long-term debt	30	0
Long-term debt	837.5	303.1
Total debt	867.5	303.1
Term Loan [Member]	'	'
Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	3.64%	'
Debt, Maturity	'2019	'
Term Loan	300	0
Revolving Credit Facility [Member]	'	'
Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	3.64%	'
Debt, Maturity	'2019	'
Revolving Credit Facility	214.9	0
Construction Loans [Member]	'	'
Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	6.12%	'
Debt, Maturity	'2018	'
Construction loans	$55.70	$6.60
Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	7.88%	'
Debt, Maturity	'2019	'

Debt_Additional_Information_De

Debt - Additional Information (Detail)

0 Months Ended

9 Months Ended

0 Months Ended

0 Months Ended

0 Months Ended

9 Months Ended

In Millions, unless otherwise specified

Aug. 15, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Nov. 18, 2013

Nov. 18, 2013

Nov. 18, 2013

Nov. 18, 2013

Nov. 18, 2013

Nov. 18, 2013

Nov. 18, 2013

Dec. 01, 2009

Sep. 30, 2014

Dec. 01, 2009

Revolving Credit Facility and Term Loan [Member]

Revolving Credit Facility and Term Loan [Member]

Revolving Credit Facility [Member]

Koppers Carbon and Chemical Company Limited [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

USD ($)

USD ($)

USD ($)

Installment

Third Party Debt [Member]

Lender [Member]

Koppers Carbon and Chemical Company Limited [Member]

Koppers Carbon and Chemical Company Limited [Member]

Koppers Carbon and Chemical Company Limited [Member]

USD ($)

CNY

Committed Credit Facility [Member]

USD ($)

CNY

CNY

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Revolving credit facility

$350

'

'

'

'

'

'

'

'

'

'

'

'

'

Revolving credit facility, current borrowing capacity

500

'

'

'

'

'

'

'

'

'

'

'

'

'

Senior secured term loan for acquiring Osmose

300

'

'

'

'

'

'

'

'

'

'

'

'

'

Revolving credit facility, Borrowing maturity date

15-Aug-19

'

'

'

'

'

'

'

'

'

'

'

'

'

Initial interest rate

3.25%

'

'

'

'

'

'

'

'

'

'

'

'

'

Quarterly principal repayment obligations interest rate

2.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

Quarterly principal repayment obligations amount

7.5

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt instrument, unused borrowing capacity

'

233

0

'

'

'

'

'

'

'

'

'

'

'

Letters of credit, amount outstanding

'

52.1

0

'

'

'

'

'

'

'

'

'

'

'

Percentage of owned subsidiary

'

'

'

60.00%

'

'

'

'

75.00%

'

'

100.00%

'

'

Construction loan facility borrowing capacity

'

'

'

'

'

'

198.8

66.2

'

44

265

'

'

'

Percentage of non-controlling shareholder

'

'

'

'

'

25.00%

'

'

'

'

'

'

'

'

Debt maturity date

'

'

'

'

18-Nov-18

'

'

'

'

'

'

'

'

'

Number of installments for repayment of loans

'

'

'

'

'

6

'

'

'

'

'

'

'

'

Installment due frequency for repayment of loan in months

'

'

'

'

'6 months

'

'

'

'

'

'

'

'

'

Commencement period of debt repayment

'

'

'

'

'2016-05

'

'

'

'

'

'

'

'

'

Debt, Weighted Average Interest Rate

'

'

3.64%

'

'

'

'

'

'

'

'

'

7.88%

'

Debt instrument, issuance date

'

'

'

'

'

'

'

'

'

'

'

'

1-Dec-09

'

Debt instrument, offering price percentage

'

'

'

'

'

'

'

'

'

'

'

98.31%

'

'

Debt instrument, offering value

'

'

'

'

'

'

'

'

'

'

'

'

'

294.9

Debt instrument, face amount

'

'

'

'

'

'

'

'

'

'

'

'

'

$300

Debt instrument, effective interest rate

'

'

'

'

'

'

'

'

'

'

'

'

8.13%

'

Debt instrument, redemption price percentage

'

'

'

'

'

'

'

'

'

'

'

'

103.94%

'

Frequency of interest payment on senior notes

'

'

'

'

'

'

'

'

'

'

'

'

'Interest on the Senior Notes is payable semiannually on December 1 and June 1 each year

'

Asset_Retirement_Obligations_S

Asset Retirement Obligations - Schedule of Changes in Carrying Values of Asset Retirement Obligations (Detail) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract]	'	'
Balance at beginning of year	$23.20	$21.50
Accretion expense	1.8	1.2
Revision in estimated cash flows, net	4.3	6.7
Cash expenditures	-2.3	-5.6
Currency translation	-0.1	-0.6
Balance at end of period	$26.90	$23.20

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, 2014	Dec. 31, 2013
Revenue Recognition [Abstract]	'	'
Balance at beginning of year	$3.20	$3.90
Revenue earned	-0.5	-0.7
Balance at end of period	$2.70	$3.20

Derivative_Financial_Instrumen1

Derivative Financial Instruments - Additional Information (Detail)	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014
In Millions, unless otherwise specified	Forward Contracts [Member]	Accrued Liabilities [Member]	Other Current Assets [Member]	Copper Swap Contracts [Member]	Copper Swap Contracts [Member]	Copper Swap Contracts [Member]	Copper Swap Contracts [Member]	Copper Swap Contracts [Member]
	USD ($)	Forward Contracts [Member]	Forward Contracts [Member]	USD ($)	USD ($)	Commodity Price [Member]	Accrued Liabilities [Member]	Accrued Liabilities [Member]
		USD ($)	USD ($)			USD ($)	USD ($)	GBP (£)
Derivative [Line Items]	'	'	'	'	'	'	'	'
Derivative, fair value, net	($0.10)	$0.30	$0.20	'	'	'	($3.30)	£ 21.9
Change in derivative financial instrument net loss	'	'	'	'	1.9	'	'	'
Ineffective portion of swap contracts charged to cost of sales	'	'	'	0.1	0.1	'	'	'
Unrealized losses, net of tax	'	'	'	'	'	$1.30	'	'

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, 2013

Sep. 30, 2012

Jul. 31, 2012

Jul. 31, 2004

Sep. 30, 2014

Dec. 31, 2013

Mar. 30, 2012

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

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

'

'

'

'

112

111

'

'

'

'

'

'

'

'

Number of cases

'

'

'

'

60

61

'

60

55

59

3

1

'

'

Compensatory damages

$3,100,000

$1,700,000

'

'

'

'

'

'

'

'

'

$15,000,000

'

'

Plant operation resumption period

'

'

'21 days

'

'

'

'

'

'

'

'

'

'

'

Environmental legal indemnification expense

'

'

'

7,000,000

'

'

'

'

'

'

'

'

'

'

Number of sites listed on National Priorities List

'

'

'

'

2

'

'

'

'

'

'

'

'

'

Environmental remediation costs paid by others, per year

'

'

'

'

'

15,000,000

'

'

'

'

'

'

'

'

Environmental Protection Agency

'

'

'

'

80

'

'

'

'

'

'

'

'

'

Possible remedial alternatives

'

'

'

'

'

'

10

'

'

'

'

'

'

'

Remedial alternatives

'

'

'

'

'

'

170,000,000

'

'

'

'

'

'

'

Remedial alternatives

'

'

'

'

'

'

1,800,000,000

'

'

'

'

'

'

'

Environmental contingencies reserve not provided by company

'

'

'

'

800,000

'

'

'

'

'

'

'

'

'

Environmental remediation expense

'

'

'

'

'

'

'

'

'

'

'

'

5,500,000

1,600,000

Amount contributable by third party

'

'

'

'

'

'

'

'

'

'

'

'

'

7,500,000

Environmental remediation reserve

'

'

'

'

400,000

1,800,000

'

'

'

'

'

'

'

1,900,000

Net amount contributed by third party

'

'

'

'

'

'

'

'

'

'

'

'

1,800,000

'

Accrued liability for environmental matters, current

'

'

'

'

$6,700,000

$8,200,000

'

'

'

'

'

'

'

'

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, 2014	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'	'
Balance at beginning of year	$11.90	$14.10
Expense	0.4	1.8
Reversal of reserves	-0.2	-1.2
Cash expenditures	-2.6	-0.9
Acquisition	0.8	0
Currency translation	0	-1.9
Balance at end of period	$10.30	$11.90

Subsidiary_Guarantor_Informati4

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Additional Information (Detail) (USD $)	0 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Dec. 01, 2009	Dec. 01, 2009	Sep. 30, 2014	Sep. 30, 2013	Aug. 15, 2014	Sep. 30, 2014
	Senior Notes [Member]	Senior Notes [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]
						Revolving Credit Facility [Member]
Debt Instrument [Line Items]	'	'	'	'	'	'
Principal value of Senior Notes	'	$300	'	'	'	'
Percent-owned material domestic subsidiaries	100.00%	'	'	'	'	'
Revolving credit facility, current borrowing capacity	'	'	'	'	500	'
Restricted net assets	'	'	'	'	'	75
Cash dividends paid	'	'	$17.80	$33.20	'	'

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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	$440.10	$395.20	$1,128.30	$1,136.50
Selling, general and administrative	32	18.3	75.3	52.2
Operating profit (loss)	17.3	39.1	31.1	92.5
Other income (expense)	-0.2	1.3	-0.3	2.8
Income taxes	9.5	14.1	9.1	29.3
(Loss) income from continuing operations	-4.3	19.6	-3.6	45.8
Discontinued operations	0.1	-0.1	0	-0.1
Noncontrolling interests	-1.5	0.4	-4.7	1.2
Net (loss) income attributable to Koppers	-2.7	19.1	1.1	44.5
Comprehensive income attributable to Koppers	-18.6	25.8	-9.2	40.8
Intersegment [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	21.5	23.3	62.8	70.9
Senior Notes [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	440.1	395.2	1,128.30	1,136.50
Cost of sales including depreciation and amortization	390.8	337.8	1,021.90	991.8
Selling, general and administrative	32	18.3	75.3	52.2
Operating profit (loss)	17.3	39.1	31.1	92.5
Other income (expense)	-0.2	1.3	-0.3	2.8
Equity income of subsidiaries	0	0	0	0
Interest expense (income)	11.9	6.7	25.3	20.2
Income taxes	9.5	14.1	9.1	29.3
(Loss) income from continuing operations	-4.3	19.6	-3.6	45.8
Discontinued operations	0.1	-0.1	0	-0.1
Noncontrolling interests	-1.5	0.4	-4.7	1.2
Net (loss) income attributable to Koppers	-2.7	19.1	1.1	44.5
Comprehensive income attributable to Koppers	-18.6	25.8	-9.2	40.8
Senior Notes [Member] | Intersegment [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	-23.3	-10.8	-44.4	-42.3
Cost of sales including depreciation and amortization	-22.9	-10.9	-44.2	-42.4
Selling, general and administrative	0	0	0	0
Operating profit (loss)	-0.4	0.1	-0.2	0.1
Other income (expense)	-1.2	-0.9	-3.3	-3.1
Equity income of subsidiaries	-4.2	-41.8	-11.3	-99.4
Interest expense (income)	-1.2	-0.9	-3.3	-3.1
Income taxes	0	0	0	0
(Loss) income from continuing operations	-4.6	-41.7	-11.5	-99.3
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net (loss) income attributable to Koppers	-4.6	-41.7	-11.5	-99.3
Comprehensive income attributable to Koppers	38.1	-50.6	19.5	-68.9
Senior Notes [Member] | Parent [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	0.3	0.5	1.3	1.5
Operating profit (loss)	-0.3	-0.5	-1.3	-1.5
Other income (expense)	0	0	0	0
Equity income of subsidiaries	-2.6	19.4	1.9	45.4
Interest expense (income)	0	0	0	0
Income taxes	-0.2	-0.2	-0.5	-0.6
(Loss) income from continuing operations	-2.7	19.1	1.1	44.5
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net (loss) income attributable to Koppers	-2.7	19.1	1.1	44.5
Comprehensive income attributable to Koppers	-18.6	25.8	-9.2	40.8
Senior Notes [Member] | Koppers Inc. [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	220.5	230.1	600.5	660.3
Cost of sales including depreciation and amortization	194.8	197.5	539.7	580.6
Selling, general and administrative	16.8	10.8	44.6	29.7
Operating profit (loss)	8.9	21.8	16.2	50
Other income (expense)	0	0.4	0.1	1.3
Equity income of subsidiaries	6.5	14.2	16.1	35.7
Interest expense (income)	11.4	6.8	24.7	20.3
Income taxes	6.6	10.2	5.8	21.3
(Loss) income from continuing operations	-2.6	19.4	1.9	45.4
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net (loss) income attributable to Koppers	-2.6	19.4	1.9	45.4
Comprehensive income attributable to Koppers	-18.4	26	-8.3	41.6
Senior Notes [Member] | Domestic Guarantor Subsidiaries [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	53.3	11.9	71.2	48.5
Cost of sales including depreciation and amortization	43.1	7.2	52.3	34.3
Selling, general and administrative	5.1	0.1	5.7	0.7
Operating profit (loss)	5.1	4.6	13.2	13.5
Other income (expense)	1.3	1	3.1	3.1
Equity income of subsidiaries	0.3	8.2	-6.7	18.3
Interest expense (income)	0	0	0	0
Income taxes	0.2	0	-5.7	0.2
(Loss) income from continuing operations	6.5	13.8	15.3	34.7
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net (loss) income attributable to Koppers	6.5	13.8	15.3	34.7
Comprehensive income attributable to Koppers	-10.1	19.3	3.5	27.7
Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	189.6	164	501	470
Cost of sales including depreciation and amortization	175.8	144	474.1	419.3
Selling, general and administrative	9.8	6.9	23.7	20.3
Operating profit (loss)	4	13.1	3.2	30.4
Other income (expense)	-0.3	0.8	-0.2	1.5
Equity income of subsidiaries	0	0	0	0
Interest expense (income)	1.7	0.8	3.9	3
Income taxes	2.9	4.1	9.5	8.4
(Loss) income from continuing operations	-0.9	9	-10.4	20.5
Discontinued operations	0.1	-0.1	0	-0.1
Noncontrolling interests	-1.5	0.4	-4.7	1.2
Net (loss) income attributable to Koppers	0.7	8.5	-5.7	19.2
Comprehensive income attributable to Koppers	($9.60)	$5.30	($14.70)	($0.40)

Subsidiary_Guarantor_Informati6

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Balance Sheet (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets	'	'	'	'
Cash and cash equivalents	$75.10	$82.20	$72.40	$66.70
Receivables, net	229.5	157.9	'	'
Inventories, net	227.7	168.8	'	'
Deferred tax assets	20.2	10	'	'
Other current assets	39.6	35.7	'	'
Total current assets	608	473.1	'	'
Equity investments	5.7	6.6	'	'
Property, plant and equipment, net	286.8	197	'	'
Goodwill	238	72.7	'	'
Intangible assets, net	180.1	12.2	'	'
Other noncurrent assets	25	14	'	'
Total assets	1,353.90	784.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	122.4	107.6	'	'
Accrued liabilities	102.6	82.4	'	'
Short-term debt and current portion of long-term debt	30	0	'	'
Total current liabilities	260.1	195.1	'	'
Long-term debt	837.5	303.1	'	'
Total liabilities	1,188.90	595.1	'	'
Koppers shareholders' equity	148.6	169.8	'	'
Noncontrolling interests	16.4	20	'	'
Total liabilities and equity	1,353.90	784.9	'	'
Senior Notes [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	75.1	82.2	72.4	66.7
Receivables, net	235.9	166.9	'	'
Affiliated receivables	0	0	'	'
Inventories, net	227.7	168.8	'	'
Deferred tax assets	20.2	10	'	'
Other current assets	49.1	45.2	'	'
Total current assets	608	473.1	'	'
Equity investments	5.7	6.6	'	'
Property, plant and equipment, net	286.8	197	'	'
Goodwill	238	72.7	'	'
Intangible assets, net	180.1	12.2	'	'
Deferred tax assets	10.3	9.3	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	25	14	'	'
Total assets	1,353.90	784.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	122.4	107.6	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	107.7	87.5	'	'
Short-term debt and current portion of long-term debt	30	'	'	'
Total current liabilities	260.1	195.1	'	'
Long-term debt	837.5	303.1	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	91.3	96.9	'	'
Total liabilities	1,188.90	595.1	'	'
Koppers shareholders' equity	148.6	169.8	'	'
Noncontrolling interests	16.4	20	'	'
Total liabilities and equity	1,353.90	784.9	'	'
Senior Notes [Member] | Intersegment [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	-22.9	-7.5	'	'
Inventories, net	-0.4	-0.2	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	-23.3	-7.7	'	'
Equity investments	-1,231.40	-689.1	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Intangible assets, net	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	-230	-173.2	'	'
Other noncurrent assets	0	0	'	'
Total assets	-1,484.70	-870	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0	0	'	'
Affiliated payables	-28.7	-14.5	'	'
Accrued liabilities	0	0	'	'
Short-term debt and current portion of long-term debt	0	'	'	'
Total current liabilities	-28.7	-14.5	'	'
Long-term debt	0	0	'	'
Affiliated debt	-230	-173.2	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	-258.7	-187.7	'	'
Koppers shareholders' equity	-1,226	-682.3	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	-1,484.70	-870	'	'
Senior Notes [Member] | Parent [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	0.1	0.2	'	'
Inventories, net	0	0	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	0.1	0.2	'	'
Equity investments	153.3	174.7	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Intangible assets, net	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	0	0	'	'
Total assets	153.4	174.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0.1	0	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	4.7	5.1	'	'
Short-term debt and current portion of long-term debt	0	'	'	'
Total current liabilities	4.8	5.1	'	'
Long-term debt	0	0	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	4.8	5.1	'	'
Koppers shareholders' equity	148.6	169.8	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	153.4	174.9	'	'
Senior Notes [Member] | Koppers Inc. [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0.2	29.9	8	4.8
Receivables, net	91.3	75.6	'	'
Affiliated receivables	4.1	1.1	'	'
Inventories, net	87.8	86.1	'	'
Deferred tax assets	7.9	7.9	'	'
Other current assets	5.5	7.3	'	'
Total current assets	196.8	207.9	'	'
Equity investments	832.1	333.5	'	'
Property, plant and equipment, net	111.9	112.2	'	'
Goodwill	39.8	39.8	'	'
Intangible assets, net	2.4	3.3	'	'
Deferred tax assets	0.5	2.4	'	'
Affiliated loan receivables	32.6	8.5	'	'
Other noncurrent assets	19.4	11.7	'	'
Total assets	1,235.50	719.3	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	52.2	48.3	'	'
Affiliated payables	14	1.9	'	'
Accrued liabilities	33.8	27.8	'	'
Short-term debt and current portion of long-term debt	30	'	'	'
Total current liabilities	130	78	'	'
Long-term debt	781.8	296.5	'	'
Affiliated debt	121	109.5	'	'
Other long-term liabilities	55.2	67.6	'	'
Total liabilities	1,088	551.6	'	'
Koppers shareholders' equity	147.5	167.7	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	1,235.50	719.3	'	'
Senior Notes [Member] | Domestic Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	1.8	0.1	0	0
Receivables, net	35.8	9.3	'	'
Affiliated receivables	8.3	3.9	'	'
Inventories, net	31.5	0	'	'
Deferred tax assets	10.9	1.5	'	'
Other current assets	1.5	0.6	'	'
Total current assets	89.8	15.4	'	'
Equity investments	247.9	182.9	'	'
Property, plant and equipment, net	51.9	0	'	'
Goodwill	162.7	0	'	'
Intangible assets, net	162.7	0	'	'
Deferred tax assets	1.1	-1.4	'	'
Affiliated loan receivables	155.9	123.8	'	'
Other noncurrent assets	3.7	0	'	'
Total assets	875.7	320.7	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	8.3	6.7	'	'
Affiliated payables	6.3	4	'	'
Accrued liabilities	19.9	0.5	'	'
Short-term debt and current portion of long-term debt	0	'	'	'
Total current liabilities	34.5	11.2	'	'
Long-term debt	0	0	'	'
Affiliated debt	32.6	8.5	'	'
Other long-term liabilities	10.8	2.5	'	'
Total liabilities	77.9	22.2	'	'
Koppers shareholders' equity	797.8	298.5	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	875.7	320.7	'	'
Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	73.1	52.2	64.4	61.9
Receivables, net	108.8	82	'	'
Affiliated receivables	10.4	2.3	'	'
Inventories, net	108.8	82.9	'	'
Deferred tax assets	1.4	0.6	'	'
Other current assets	42.1	37.3	'	'
Total current assets	344.6	257.3	'	'
Equity investments	3.8	4.6	'	'
Property, plant and equipment, net	123	84.8	'	'
Goodwill	35.5	32.9	'	'
Intangible assets, net	15	8.9	'	'
Deferred tax assets	8.7	8.3	'	'
Affiliated loan receivables	41.5	40.9	'	'
Other noncurrent assets	1.9	2.3	'	'
Total assets	574	440	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	61.8	52.6	'	'
Affiliated payables	8.4	8.6	'	'
Accrued liabilities	49.3	54.1	'	'
Short-term debt and current portion of long-term debt	0	'	'	'
Total current liabilities	119.5	115.3	'	'
Long-term debt	55.7	6.6	'	'
Affiliated debt	76.4	55.2	'	'
Other long-term liabilities	25.3	26.8	'	'
Total liabilities	276.9	203.9	'	'
Koppers shareholders' equity	280.7	216.1	'	'
Noncontrolling interests	16.4	20	'	'
Total liabilities and equity	$574	$440	'	'

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, 2014	Sep. 30, 2013
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	$10.80	$65.60
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-59	-29.4
Net cash proceeds (payments) from divestitures and asset sales	0.1	2.4
Net cash provided by (used in) investing activities	-555.4	-27
Cash provided by (used in) financing activities:	'	'
Deferred financing costs	-11.1	-1.2
Dividends paid	-15.2	-15.3
Net cash provided by (used in) financing activities	537.6	-31.5
Effect of exchange rates on cash	-0.1	-1.4
Net increase (decrease) in cash and cash equivalents	-7.1	5.7
Cash and cash equivalents at beginning of period	82.2	66.7
Cash and cash equivalents at end of period	75.1	72.4
Senior Notes [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	10.8	65.6
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-555.5	-29.4
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0.1	2.4
Net cash provided by (used in) investing activities	-555.4	-27
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	563.8	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	-11.1	-1.2
Other financing activities	1.4	2.3
Dividends paid	-15.2	-15.3
Stock issued (repurchased)	-1.3	-17.3
Net cash provided by (used in) financing activities	537.6	-31.5
Effect of exchange rates on cash	-0.1	-1.4
Net increase (decrease) in cash and cash equivalents	-7.1	5.7
Cash and cash equivalents at beginning of period	82.2	66.7
Cash and cash equivalents at end of period	75.1	72.4
Senior Notes [Member] | Intersegment [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	-26.7	-36.3
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	14.8	0
(Loans to) repayments from affiliates	58.8	11.7
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	73.6	11.7
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	-58.8	-11.7
Deferred financing costs	0	0
Other financing activities	0	0
Dividends paid	26.7	36.3
Stock issued (repurchased)	-14.8	0
Net cash provided by (used in) financing activities	-46.9	24.6
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 period	0	0
Cash and cash equivalents at end of period	0	0
Senior Notes [Member] | Parent [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	16.5	32.6
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	0	0
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	0	0
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	0	0
Other financing activities	0	0
Dividends paid	-15.2	-15.3
Stock issued (repurchased)	-1.3	-17.3
Net cash provided by (used in) financing activities	-16.5	-32.6
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 period	0	0
Cash and cash equivalents at end of period	0	0
Senior Notes [Member] | Koppers Inc. [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	-0.9	43.7
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	508	-13.3
(Loans to) repayments from affiliates	-24.4	-3
Net cash proceeds (payments) from divestitures and asset sales	0.1	1.4
Net cash provided by (used in) investing activities	-532.3	-14.9
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	514.9	'
Borrowings (repayments) of affiliated debt	17.5	8.7
Deferred financing costs	-11.1	-1.2
Other financing activities	0	0
Dividends paid	-17.8	-33.2
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	503.5	-25.7
Effect of exchange rates on cash	0	0.1
Net increase (decrease) in cash and cash equivalents	-29.7	3.2
Cash and cash equivalents at beginning of period	29.9	4.8
Cash and cash equivalents at end of period	0.2	8
Senior Notes [Member] | Domestic Guarantor Subsidiaries [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	26.4	2.5
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-15.1	0
(Loans to) repayments from affiliates	-33.9	-5.5
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	-49	-5.5
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	24.3	3
Deferred financing costs	0	0
Other financing activities	0	0
Dividends paid	0	0
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	24.3	3
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	1.7	0
Cash and cash equivalents at beginning of period	0.1	0
Cash and cash equivalents at end of period	1.8	0
Senior Notes [Member] | Non-Guarantor Subsidiaries [Member]	'	'
Subsidiary, Sale of Stock [Line Items]	'	'
Cash provided by (used in) operating activities	-4.5	23.1
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-47.2	-16.1
(Loans to) repayments from affiliates	-0.5	-3.2
Net cash proceeds (payments) from divestitures and asset sales	0	1
Net cash provided by (used in) investing activities	-47.7	-18.3
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	48.9	'
Borrowings (repayments) of affiliated debt	17	0
Deferred financing costs	0	0
Other financing activities	1.4	2.3
Dividends paid	-8.9	-3.1
Stock issued (repurchased)	14.8	0
Net cash provided by (used in) financing activities	73.2	0.8
Effect of exchange rates on cash	-0.1	-1.5
Net increase (decrease) in cash and cash equivalents	20.9	2.5
Cash and cash equivalents at beginning of period	52.2	61.9
Cash and cash equivalents at end of period	$73.10	$64.40

Subsidiary_Guarantor_Informati8

Subsidiary Guarantor Information for Shelf Registration - Additional Information (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Aug. 15, 2014
Subsidiary Guarantor Information for Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'
Cash dividends paid	$17.80	$33.20	'
Subsidiary Guarantor Information for Shelf Registration [Member] | Revolving Credit Facility [Member]	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'
Restricted net assets	75	'	'
Payment Guarantee by Subsidiaries for Senior Notes [Member]	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'
Revolving credit facility, current borrowing capacity	'	'	500
Cash dividends paid	$17.80	$33.20	'
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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	$440.10	$395.20	$1,128.30	$1,136.50
Selling, general and administrative	32	18.3	75.3	52.2
Operating profit (loss)	17.3	39.1	31.1	92.5
Other income (expense)	-0.2	1.3	-0.3	2.8
Income taxes	9.5	14.1	9.1	29.3
Income from continuing operations	-4.3	19.6	-3.6	45.8
Discontinued operations	0.1	-0.1	0	-0.1
Noncontrolling interests	-1.5	0.4	-4.7	1.2
Net income attributable to Koppers	-2.7	19.1	1.1	44.5
Comprehensive income attributable to Koppers	-18.6	25.8	-9.2	40.8
Intersegment [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	21.5	23.3	62.8	70.9
Shelf Registration [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	440.1	395.2	1,128.30	1,136.50
Cost of sales including depreciation and amortization	390.8	337.8	1,021.90	991.8
Selling, general and administrative	32	18.3	75.3	52.2
Operating profit (loss)	17.3	39.1	31.1	92.5
Other income (expense)	-0.2	1.3	-0.3	2.8
Equity income of subsidiaries	0	0	0	0
Interest expense (income)	11.9	6.7	25.3	20.2
Income taxes	9.5	14.1	9.1	29.3
Income from continuing operations	-4.3	19.6	-3.6	45.8
Discontinued operations	0.1	-0.1	0	-0.1
Noncontrolling interests	-1.5	0.4	-4.7	1.2
Net income attributable to Koppers	-2.7	19.1	1.1	44.5
Comprehensive income attributable to Koppers	-18.6	25.8	-9.2	40.8
Shelf Registration [Member] | Intersegment [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	-22.2	-10.9	-43.6	-44.8
Cost of sales including depreciation and amortization	-22	-11	-43.6	-44.9
Selling, general and administrative	0	0	0	0
Operating profit (loss)	-0.2	0.1	0	0.1
Other income (expense)	-1.1	-0.9	-3.2	-3.1
Equity income of subsidiaries	0.7	-42.3	-1.4	-100.9
Interest expense (income)	-1.1	-0.8	-3.2	-3.1
Income taxes	0	0	0	0
Income from continuing operations	0.5	-42.3	-1.4	-100.8
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	0.5	-42.3	-1.4	-100.8
Comprehensive income attributable to Koppers	47.1	-57.1	28.1	-83.1
Shelf Registration [Member] | Parent [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	0.3	0.5	1.3	1.5
Operating profit (loss)	-0.3	-0.5	-1.3	-1.5
Other income (expense)	0	0	0	0
Equity income of subsidiaries	-2.6	19.4	1.9	45.4
Interest expense (income)	0	0	0	0
Income taxes	-0.2	-0.2	-0.5	-0.6
Income from continuing operations	-2.7	19.1	1.1	44.5
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	-2.7	19.1	1.1	44.5
Comprehensive income attributable to Koppers	-18.6	25.8	-9.2	40.8
Shelf Registration [Member] | Koppers Inc. [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	220.5	230.1	600.5	660.3
Cost of sales including depreciation and amortization	194.8	197.5	539.7	580.6
Selling, general and administrative	16.8	10.8	44.6	29.7
Operating profit (loss)	8.9	21.8	16.2	50
Other income (expense)	0	0.4	0.1	1.3
Equity income of subsidiaries	6.5	14.2	16.1	35.7
Interest expense (income)	11.4	6.8	24.7	20.3
Income taxes	6.6	10.2	5.8	21.3
Income from continuing operations	-2.6	19.4	1.9	45.4
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	-2.6	19.4	1.9	45.4
Comprehensive income attributable to Koppers	-18.4	26	-8.3	41.6
Shelf Registration [Member] | Domestic Guarantor Subsidiaries [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	17.1	11.9	35	48.5
Cost of sales including depreciation and amortization	13.6	7.2	22.8	34.3
Selling, general and administrative	0.2	0.1	0.8	0.7
Operating profit (loss)	3.3	4.6	11.4	13.5
Other income (expense)	1.2	1	3	3.1
Equity income of subsidiaries	-0.4	8.2	-7.4	18.3
Interest expense (income)	0	0	0	0
Income taxes	0.2	0	-5.7	0.2
Income from continuing operations	3.9	13.8	12.7	34.7
Discontinued operations	0	0	0	0
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	3.9	13.8	12.7	34.7
Comprehensive income attributable to Koppers	-12.4	14.5	1.1	22.8
Shelf Registration [Member] | Foreign Guarantor Subsidiaries [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	103	120.8	321.1	348.7
Cost of sales including depreciation and amortization	91	103.7	291.7	305.8
Selling, general and administrative	5.2	5.5	16.4	16.8
Operating profit (loss)	6.8	11.6	13	26.1
Other income (expense)	0	0.7	0.1	0.8
Equity income of subsidiaries	-4.1	0.4	-9.2	1.4
Interest expense (income)	1	0.7	2.4	2.5
Income taxes	2.5	3.8	8.9	7.4
Income from continuing operations	-0.8	8.2	-7.4	18.4
Discontinued operations	0	-0.1	0	-0.1
Noncontrolling interests	0	0	0	0
Net income attributable to Koppers	-0.8	8.1	-7.4	18.3
Comprehensive income attributable to Koppers	-10.4	13.7	-14.4	15.8
Shelf Registration [Member] | Non-Guarantor Subsidiaries [Member]	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'
Net sales	121.7	43.3	215.3	123.8
Cost of sales including depreciation and amortization	113.4	40.4	211.3	116
Selling, general and administrative	9.5	1.4	12.2	3.5
Operating profit (loss)	-1.2	1.5	-8.2	4.3
Other income (expense)	-0.3	0.1	-0.3	0.7
Equity income of subsidiaries	-0.1	0.1	0	0.1
Interest expense (income)	0.6	0	1.4	0.5
Income taxes	0.4	0.3	0.6	1
Income from continuing operations	-2.6	1.4	-10.5	3.6
Discontinued operations	0.1	0	0	0
Noncontrolling interests	-1.5	0.4	-4.7	1.2
Net income attributable to Koppers	-1	1	-5.8	2.4
Comprehensive income attributable to Koppers	($5.90)	$2.90	($6.50)	$2.90

Recovered_Sheet1

Subsidiary Guarantor Information for Shelf Registration - Condensed Consolidating Balance Sheet (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets	'	'	'	'
Cash and cash equivalents	$75.10	$82.20	$72.40	$66.70
Receivables, net	229.5	157.9	'	'
Inventories, net	227.7	168.8	'	'
Deferred tax assets	20.2	10	'	'
Other current assets	39.6	35.7	'	'
Total current assets	608	473.1	'	'
Equity investments	5.7	6.6	'	'
Property, plant and equipment, net	286.8	197	'	'
Goodwill	238	72.7	'	'
Intangible assets, net	180.1	12.2	'	'
Deferred tax assets	10.3	9.3	'	'
Other noncurrent assets	25	14	'	'
Total assets	1,353.90	784.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	122.4	107.6	'	'
Accrued liabilities	102.6	82.4	'	'
Short-term debt and current portion of long-term debt	30	0	'	'
Total current liabilities	260.1	195.1	'	'
Long-term debt	837.5	303.1	'	'
Total liabilities	1,188.90	595.1	'	'
Koppers shareholders' equity	148.6	169.8	'	'
Noncontrolling interests	16.4	20	'	'
Total liabilities and equity	1,353.90	784.9	'	'
Shelf Registration [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	75.1	82.2	72.4	66.7
Receivables, net	235.9	166.9	'	'
Affiliated receivables	0	0	'	'
Inventories, net	227.7	168.8	'	'
Deferred tax assets	20.2	10	'	'
Other current assets	49.1	45.2	'	'
Total current assets	608	473.1	'	'
Equity investments	5.7	6.6	'	'
Property, plant and equipment, net	286.8	197	'	'
Goodwill	238	72.7	'	'
Intangible assets, net	180.1	12.2	'	'
Deferred tax assets	10.3	9.3	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	25	14	'	'
Total assets	1,353.90	784.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	122.4	107.6	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	107.7	87.5	'	'
Short-term debt and current portion of long-term debt	30	'	'	'
Total current liabilities	260.1	195.1	'	'
Long-term debt	837.5	303.1	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	91.3	96.9	'	'
Total liabilities	1,188.90	595.1	'	'
Koppers shareholders' equity	148.6	169.8	'	'
Noncontrolling interests	16.4	20	'	'
Total liabilities and equity	1,353.90	784.9	'	'
Shelf Registration [Member] | Intersegment [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	-20.7	-7.6	'	'
Inventories, net	-0.2	-0.2	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	-20.9	-7.8	'	'
Equity investments	-1,203.90	-739.5	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Intangible assets, net	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	-230	-173.2	'	'
Other noncurrent assets	0.1	0	'	'
Total assets	-1,454.70	-920.5	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0	0	'	'
Affiliated payables	-26.5	-14.7	'	'
Accrued liabilities	0	0	'	'
Short-term debt and current portion of long-term debt	0	'	'	'
Total current liabilities	-26.5	-14.7	'	'
Long-term debt	0	0	'	'
Affiliated debt	-230	-173.2	'	'
Other long-term liabilities	0.1	0	'	'
Total liabilities	-256.4	-187.9	'	'
Koppers shareholders' equity	-1,198.30	-732.6	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	-1,454.70	-920.5	'	'
Shelf Registration [Member] | Parent [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	0.1	0.2	'	'
Inventories, net	0	0	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	0.1	0.2	'	'
Equity investments	153.3	174.7	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Intangible assets, net	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	0	0	'	'
Total assets	153.4	174.9	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0.1	0	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	4.7	5.1	'	'
Short-term debt and current portion of long-term debt	0	'	'	'
Total current liabilities	4.8	5.1	'	'
Long-term debt	0	0	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	4.8	5.1	'	'
Koppers shareholders' equity	148.6	169.8	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	153.4	174.9	'	'
Shelf Registration [Member] | Koppers Inc. [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0.2	29.9	8	4.8
Receivables, net	91.3	75.6	'	'
Affiliated receivables	4.1	1.1	'	'
Inventories, net	87.8	86.1	'	'
Deferred tax assets	7.9	7.9	'	'
Other current assets	5.5	7.3	'	'
Total current assets	196.8	207.9	'	'
Equity investments	832.1	333.5	'	'
Property, plant and equipment, net	111.9	112.2	'	'
Goodwill	39.8	39.8	'	'
Intangible assets, net	2.4	3.3	'	'
Deferred tax assets	0.5	2.4	'	'
Affiliated loan receivables	32.6	8.5	'	'
Other noncurrent assets	19.4	11.7	'	'
Total assets	1,235.50	719.3	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	52.2	48.3	'	'
Affiliated payables	14	1.9	'	'
Accrued liabilities	33.8	27.8	'	'
Short-term debt and current portion of long-term debt	30	'	'	'
Total current liabilities	130	78	'	'
Long-term debt	781.8	296.5	'	'
Affiliated debt	121	109.5	'	'
Other long-term liabilities	55.2	67.6	'	'
Total liabilities	1,088	551.6	'	'
Koppers shareholders' equity	147.5	167.7	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	1,235.50	719.3	'	'
Shelf Registration [Member] | Domestic Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	0.1	0.1	0	0
Receivables, net	10.7	9.3	'	'
Affiliated receivables	-2.8	3.9	'	'
Inventories, net	0	0	'	'
Deferred tax assets	3.9	1.5	'	'
Other current assets	0.4	0.6	'	'
Total current assets	12.3	15.4	'	'
Equity investments	175.5	182.9	'	'
Property, plant and equipment, net	0.9	0	'	'
Goodwill	0	0	'	'
Intangible assets, net	0	0	'	'
Deferred tax assets	2.3	-1.4	'	'
Affiliated loan receivables	155.9	123.8	'	'
Other noncurrent assets	0	0	'	'
Total assets	346.9	320.7	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0	6.7	'	'
Affiliated payables	6.3	4	'	'
Accrued liabilities	0.4	0.5	'	'
Short-term debt and current portion of long-term debt	0	'	'	'
Total current liabilities	6.7	11.2	'	'
Long-term debt	0	0	'	'
Affiliated debt	32.6	8.5	'	'
Other long-term liabilities	2.5	2.5	'	'
Total liabilities	41.8	22.2	'	'
Koppers shareholders' equity	305.1	298.5	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	346.9	320.7	'	'
Shelf Registration [Member] | Foreign Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	31.9	43.5	48.3	40.7
Receivables, net	43.1	55.5	'	'
Affiliated receivables	6.4	0.8	'	'
Inventories, net	66.9	75.2	'	'
Deferred tax assets	0	0	'	'
Other current assets	12.7	17.5	'	'
Total current assets	161	192.5	'	'
Equity investments	44.9	50.5	'	'
Property, plant and equipment, net	40	38.1	'	'
Goodwill	30.7	31.5	'	'
Intangible assets, net	8.3	8.9	'	'
Deferred tax assets	5.1	5.5	'	'
Affiliated loan receivables	0.1	0.1	'	'
Other noncurrent assets	0.8	1	'	'
Total assets	290.9	328.1	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	28	40.6	'	'
Affiliated payables	2.5	0.4	'	'
Accrued liabilities	29	31.4	'	'
Short-term debt and current portion of long-term debt	0	'	'	'
Total current liabilities	59.5	72.4	'	'
Long-term debt	0	0	'	'
Affiliated debt	54.7	55.2	'	'
Other long-term liabilities	17.7	19.6	'	'
Total liabilities	131.9	147.2	'	'
Koppers shareholders' equity	159	180.9	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	290.9	328.1	'	'
Shelf Registration [Member] | Non-Guarantor Subsidiaries [Member]	'	'	'	'
Assets	'	'	'	'
Cash and cash equivalents	42.9	8.7	16.1	21.2
Receivables, net	90.8	26.5	'	'
Affiliated receivables	12.9	1.6	'	'
Inventories, net	73.2	7.7	'	'
Deferred tax assets	8.4	0.6	'	'
Other current assets	30.5	19.8	'	'
Total current assets	258.7	64.9	'	'
Equity investments	3.8	4.5	'	'
Property, plant and equipment, net	134	46.7	'	'
Goodwill	167.5	1.4	'	'
Intangible assets, net	169.4	0	'	'
Deferred tax assets	2.4	2.8	'	'
Affiliated loan receivables	41.4	40.8	'	'
Other noncurrent assets	4.7	1.3	'	'
Total assets	781.9	162.4	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	42.1	12	'	'
Affiliated payables	3.7	8.4	'	'
Accrued liabilities	39.8	22.7	'	'
Short-term debt and current portion of long-term debt	0	'	'	'
Total current liabilities	85.6	43.1	'	'
Long-term debt	55.7	6.6	'	'
Affiliated debt	21.7	0	'	'
Other long-term liabilities	15.8	7.2	'	'
Total liabilities	178.8	56.9	'	'
Koppers shareholders' equity	586.7	85.5	'	'
Noncontrolling interests	16.4	20	'	'
Total liabilities and equity	$781.90	$162.40	'	'

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, 2014	Sep. 30, 2013
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	$10.80	$65.60
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-59	-29.4
Net cash proceeds (payments) from divestitures and asset sales	0.1	2.4
Net cash provided by (used in) investing activities	-555.4	-27
Cash provided by (used in) financing activities:	'	'
Deferred financing costs	-11.1	-1.2
Dividends paid	-15.2	-15.3
Net cash provided by (used in) financing activities	537.6	-31.5
Effect of exchange rates on cash	-0.1	-1.4
Net increase (decrease) in cash and cash equivalents	-7.1	5.7
Cash and cash equivalents at beginning of period	82.2	66.7
Cash and cash equivalents at end of period	75.1	72.4
Shelf Registration [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	10.8	65.6
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-555.5	-29.4
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0.1	2.4
Net cash provided by (used in) investing activities	-555.4	-27
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	563.8	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	-11.1	-1.2
Other financing activities	1.4	2.3
Dividends paid	-15.2	-15.3
Stock issued (repurchased)	-1.3	-17.3
Net cash provided by (used in) financing activities	537.6	-31.5
Effect of exchange rates on cash	-0.1	-1.4
Net increase (decrease) in cash and cash equivalents	-7.1	5.7
Cash and cash equivalents at beginning of period	82.2	66.7
Cash and cash equivalents at end of period	75.1	72.4
Shelf Registration [Member] | Intersegment [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	-26.7	-36.3
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	18.9	7.7
(Loans to) repayments from affiliates	58.8	11.7
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	77.7	19.4
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	-58.8	-11.7
Deferred financing costs	0	0
Other financing activities	0	0
Dividends paid	26.7	36.3
Stock issued (repurchased)	-18.9	-7.7
Net cash provided by (used in) financing activities	-51	16.9
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 period	0	0
Cash and cash equivalents at end of period	0	0
Shelf Registration [Member] | Parent [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	16.5	32.6
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	0	0
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	0	0
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	0	0
Other financing activities	0	0
Dividends paid	-15.2	-15.3
Stock issued (repurchased)	-1.3	-17.3
Net cash provided by (used in) financing activities	-16.5	-32.6
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 period	0	0
Cash and cash equivalents at end of period	0	0
Shelf Registration [Member] | Koppers Inc. [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	-0.9	43.7
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-508	-13.3
(Loans to) repayments from affiliates	-24.4	-3
Net cash proceeds (payments) from divestitures and asset sales	-0.1	1.4
Net cash provided by (used in) investing activities	-532.3	-14.9
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	514.9	'
Borrowings (repayments) of affiliated debt	17.5	8.7
Deferred financing costs	-11.1	-1.2
Other financing activities	0	0
Dividends paid	-17.8	-33.2
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	503.5	-25.7
Effect of exchange rates on cash	0	0.1
Net increase (decrease) in cash and cash equivalents	-29.7	3.2
Cash and cash equivalents at beginning of period	29.9	4.8
Cash and cash equivalents at end of period	0.2	8
Shelf Registration [Member] | Domestic Guarantor Subsidiaries [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	19.1	2.5
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-15.7	0
(Loans to) repayments from affiliates	-27.7	-5.5
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	-43.4	-5.5
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	24.3	3
Deferred financing costs	0	0
Other financing activities	0	0
Dividends paid	0	0
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	24.3	3
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0.1	0
Cash and cash equivalents at end of period	0.1	0
Shelf Registration [Member] | Foreign Guarantor Subsidiaries [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	11.4	25.8
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-14.1	-14.3
(Loans to) repayments from affiliates	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	1
Net cash provided by (used in) investing activities	-14.1	-13.3
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	0	'
Borrowings (repayments) of affiliated debt	0	0
Deferred financing costs	0	0
Other financing activities	0	0
Dividends paid	-8.9	-3.1
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	-8.9	-3.1
Effect of exchange rates on cash	0	-1.8
Net increase (decrease) in cash and cash equivalents	-11.6	7.6
Cash and cash equivalents at beginning of period	43.5	40.7
Cash and cash equivalents at end of period	31.9	48.3
Shelf Registration [Member] | Non-Guarantor Subsidiaries [Member]	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'
Cash provided by (used in) operating activities	-8.6	-2.7
Cash provided by (used in) investing activities:	'	'
Capital expenditures and acquisitions	-36.6	-9.5
(Loans to) repayments from affiliates	-6.7	-3.2
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	-43.3	-12.7
Cash provided by (used in) financing activities:	'	'
Borrowings (repayments) of long-term debt	48.9	'
Borrowings (repayments) of affiliated debt	17	0
Deferred financing costs	0	0
Other financing activities	1.4	2.3
Dividends paid	0	0
Stock issued (repurchased)	18.9	7.7
Net cash provided by (used in) financing activities	86.2	10
Effect of exchange rates on cash	-0.1	0.3
Net increase (decrease) in cash and cash equivalents	34.2	-5.1
Cash and cash equivalents at beginning of period	8.7	21.2
Cash and cash equivalents at end of period	$42.90	$16.10

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Related Party Transactions [Abstract]	'	'
Loan to related party	$9.50	$9.50
Ownership percentage	30.00%	'
Loan repayable date	'2014-11	'
Loan repayment extended period	'1 year	'