Koppers (KOP) 10-K 3 Mar 14 2013 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Jan. 31, 2014	Jun. 30, 2013
Document And Entity Information [Abstract]	'	'	'
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	31-Dec-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Entity Registrant Name	'Koppers Holdings Inc.	'	'
Entity Central Index Key	'0001315257	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Well-known Seasoned Issuer	'Yes	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	20,634,103	'
Entity Public Float	'	'	$774

Consolidated_Statement_of_Inco

Consolidated Statement of Income (USD $)	12 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]	'	'	'
Net sales	$1,478.30	$1,555	$1,466.20
Cost of sales (excluding items below)	1,264.70	1,324.60	1,242.30
Depreciation and amortization	29.7	27.6	26.9
Impairment charges	11.9	0.6	0
Selling, general and administrative expenses	71.7	75.6	74.3
Operating profit (loss)	100.3	126.6	122.7
Other income	3.5	1.9	0.7
Interest expense	26.8	27.9	27.2
Income before income taxes	77	100.6	96.2
Income taxes	36.8	33.3	38.7
Income from continuing operations	40.2	67.3	57.5
Loss from discontinued operations, net of tax benefit of $0.1, $0.2 and $23.8	-0.1	-0.1	-19.9
Net income	40.1	67.2	37.6
Net income (loss) attributable to noncontrolling interests	-0.3	1.6	0.7
Net income attributable to Koppers	$40.40	$65.60	$36.90
Basic -	'	'	'
Continuing operations	$1.96	$3.18	$2.75
Discontinued operations	$0	($0.01)	($0.96)
Earnings per basic common share	$1.96	$3.17	$1.79
Diluted -	'	'	'
Continuing operations	$1.94	$3.14	$2.72
Discontinued operations	$0	($0.01)	($0.95)
Earnings per diluted common share	$1.94	$3.13	$1.77
Weighted average common shares outstanding (in thousands):	'	'	'
Basic	20,575	20,681	20,599
Diluted	20,815	20,927	20,833
Dividends declared per common share	$1	$0.96	$0.88

Consolidated_Statement_of_Inco1

Consolidated Statement of Income (Parenthetical) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]	'	'	'
Loss from discontinued operations, tax benefit	$0.10	$0.20	$23.80

Consolidated_Statement_of_Comp

Consolidated Statement of Comprehensive Income (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]	'	'	'
Net income	$40.10	$67.20	$37.60
Changes in other comprehensive income (loss):	'	'	'
Currency translation adjustment	-0.6	4	-2
Foreign currency transactions of long-term subsidiary investments	-9.4	1.8	-0.5
Unrecognized pension transition asset, net of tax of $0.0, $0.1 and $0.1	0	-0.3	-0.2
Unrecognized pension prior service cost, net of tax of $(0.7), $0.0 and $0.0	1.1	0	0.1
Unrecognized pension net gain (loss), net of tax of $(12.8), $(2.3) and $9.2	21.3	2.8	-14.9
Total comprehensive income	52.5	75.5	20.1
Comprehensive income attributable to noncontrolling interests	0.2	1.8	1.2
Comprehensive income attributable to Koppers	$52.30	$73.70	$18.90

Consolidated_Statement_of_Comp1

Consolidated Statement of Comprehensive Income (Parenthetical) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]	'	'	'
Unrecognized pension transition asset, tax	$0	$0.10	$0.10
Unrecognized pension prior service cost, tax	-0.7	0	0
Unrecognized pension net gain (loss), tax	($12.80)	($2.30)	$9.20

Consolidated_Balance_Sheet

Consolidated Balance Sheet (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
ASSETS	'	'
Cash and cash equivalents	$82.20	$66.70
Accounts receivable, net of allowance of $3.6 and $3.7	157.9	162.7
Income tax receivable	9	1.6
Inventories, net	168.8	195.8
Deferred tax assets	10	15.1
Loan to related party	9.5	9.5
Other current assets	35.7	29.8
Total current assets	473.1	481.2
Equity in non-consolidated investments	6.6	5.8
Property, plant and equipment, net	197	161.1
Goodwill	72.7	75.6
Deferred tax assets	9.3	27.2
Other assets	26.2	29.1
Total assets	784.9	780
Liabilities	'	'
Accounts payable	107.6	103.5
Accrued liabilities	82.4	72.1
Dividends payable	5.1	5.6
Total current liabilities	195.1	181.2
Long-term debt	303.1	296.1
Accrued postretirement benefits	41.6	89.9
Deferred tax liabilities	14.7	3.2
Other long-term liabilities	40.6	41.5
Total liabilities	595.1	611.9
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; 21,722,492 and 21,585,129 shares issued	0.2	0.2
Additional paid-in capital	158.9	153.3
Retained earnings	71.3	52
Accumulated other comprehensive loss	-10.2	-22
Treasury stock, at cost; 1,390,494 and 951,026 shares	-50.4	-32.9
Total Koppers shareholders' equity	169.8	150.6
Noncontrolling interests	20	17.5
Total equity	189.8	168.1
Total liabilities and equity	$784.90	$780

Consolidated_Balance_Sheet_Par

Consolidated Balance Sheet (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, except Share data, unless otherwise specified
Statement Of Financial Position [Abstract]	'	'
Accounts receivable, allowance	$3.60	$3.70
Senior Convertible Preferred Stock, par value	$0.01	$0.01
Senior Convertible Preferred Stock, shares authorized	10,000,000	10,000,000
Senior Convertible Preferred Stock, shares issued	0	0
Common Stock, par value	$0.01	$0.01
Common Stock, shares authorized	40,000,000	40,000,000
Common Stock, shares issued	21,722,492	21,585,129
Treasury stock, shares	1,390,494	951,026

Consolidated_Statement_of_Cash

Consolidated Statement of Cash Flows (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash provided by (used in) operating activities	'	'	'
Net income	$40.10	$67.20	$37.60
Adjustments to reconcile net cash provided by operating activities:	'	'	'
Depreciation and amortization	29.7	27.6	48.8
Impairment charges	11.9	0.6	0
(Gain) loss on sale of assets	-2.3	0.1	-0.2
Deferred income taxes	19.5	8	-11.3
Non-cash interest expense	1.7	1.7	1.6
Equity income of affiliated companies	-0.8	-0.8	-0.2
Change in other liabilities	-16.4	-11.2	6.7
Stock-based compensation	4.3	6.9	5.3
Other	0.5	-1.1	-3
Decrease (increase) in working capital:	'	'	'
Accounts receivable	2.9	-0.2	-33.2
Inventories	21.6	-26.5	5.1
Accounts payable	4.9	-0.1	15.3
Accrued liabilities and other working capital	0	5.6	4.4
Net cash provided by operating activities	117.6	77.8	76.9
Cash provided by (used in) investing activities	'	'	'
Capital expenditures	-72.9	-28.9	-33.2
Acquisitions, net of cash acquired	-2.3	-14	-0.6
Net cash proceeds (payments) from loan to related party	0	2.2	-11.7
Net cash proceeds from divestitures and asset sales	2.9	0.8	0.8
Net cash used in investing activities	-72.3	-39.9	-44.7
Cash provided by (used in) financing activities	'	'	'
Borrowings of revolving credit	97.9	259.4	218
Repayments of revolving credit	-97.9	-265.8	-211.6
Borrowings of long-term debt	6.6	0	0
Repayments on long-term debt	0	0	-1
Issuances of Common Stock	0.2	1.5	0.3
Repurchases of Common Stock	-17.5	-8.1	-0.3
Proceeds from issuance of noncontrolling interest	2.3	3.7	0
Excess tax benefit from employee stock plans	0.5	1.6	0
Payment of deferred financing costs	-1.3	-0.1	-0.5
Dividends paid	-21.1	-19.5	-18.2
Net cash provided by (used in) financing activities	-30.3	-27.3	-13.3
Effect of exchange rates on cash	0.5	2	-0.1
Net increase in cash and cash equivalents	15.5	12.6	18.8
Cash and cash equivalents at beginning of year	66.7	54.1	35.3
Cash and cash equivalents at end of period	82.2	66.7	54.1
Cash paid during the year for:	'	'	'
Interest	25.1	26	25.8
Income taxes	$20.50	$13.60	$25.70

Consolidated_Statement_of_Shar

Consolidated Statement of Shareholders' Equity (USD $)

Total

Senior Convertible Preferred Stock [Member]

Common Stock [Member]

Additional Paid-in Capital [Member]

Retained Earnings (Deficit) [Member]

Accumulated Other Comprehensive Loss [Member]

Accumulated Other Comprehensive Loss [Member]

Accumulated Other Comprehensive Loss [Member]

Accumulated Other Comprehensive Loss [Member]

Accumulated Other Comprehensive Loss [Member]

Treasury Stock [Member]

Total Koppers Shareholders' Equity - End of Year [Member]

Noncontrolling Interests [Member]

In Millions

Currency Translation Adjustment [Member]

Unrecognized Pension Transition Asset [Member]

Unrecognized Pension Prior Service Cost [Member]

Unrecognized Pension Net Loss [Member]

Balance at Dec. 31, 2010

'

$0

$0.20

$137

($11.70)

'

$31.70

$0.50

($0.30)

($44.20)

($24.50)

'

$11.20

Change in currency translation adjustment excluding foreign currency transactions of long-term subsidiary investments

-2

'

'

'

'

-2.4

'

'

'

'

'

'

'

Net income (loss) attributable to noncontrolling interests

0.7

'

'

'

'

'

'

'

'

'

'

'

0.7

Net income attributable to Koppers

36.9

'

'

'

36.9

'

'

'

'

'

'

'

'

Reclassification of unrecognized pension prior service cost to expense, net of tax expense of $0.1, $0.0 and $0.0

'

'

'

'

'

'

'

'

0.1

'

'

'

'

Reclassification of unrecognized pension net loss to expense, net of tax expense of $2.8, $3.1 and $2.4

'

'

'

'

'

'

'

'

'

4

'

'

'

Employee stock plans

'

'

'

5.9

'

'

'

'

'

'

'

'

'

Change in foreign currency transactions of long-term subsidiary investments

'

'

'

'

'

'

-0.5

'

'

'

'

'

'

Reclassification of unrecognized pension transition asset to expense, net of tax benefit of $0.0, $0.1 and $0.1

-0.2

'

'

'

'

'

'

-0.2

'

'

'

'

'

Purchases

'

'

'

'

'

'

'

'

'

'

-0.3

'

'

Investment in noncontrolling interests

'

'

'

'

'

'

'

'

'

'

'

'

0

Common Stock dividends

'

'

'

'

-18.5

'

'

'

'

'

'

'

'

Revaluation of unrecognized pension prior service cost, net of tax expense of $0.6, $0.0 and $0.0

'

'

'

'

'

'

'

'

0

'

'

'

'

Revaluation of unrecognized pension net loss, net of tax expense (benefit) of $10.0, $(0.9) and $(11.7)

'

'

'

'

'

'

'

'

'

-18.9

'

'

'

Currency translation adjustment

'

'

'

'

'

'

'

'

'

'

'

'

0.5

Total equity - end of year

107.2

'

'

'

'

'

'

'

'

'

'

'

'

Balance at Dec. 31, 2011

'

0

0.2

142.9

6.7

-30.2

28.8

0.3

-0.2

-59.1

-24.8

94.8

12.4

Change in currency translation adjustment excluding foreign currency transactions of long-term subsidiary investments

4

'

'

'

'

3.9

'

'

'

'

'

'

'

Net income (loss) attributable to noncontrolling interests

1.6

'

'

'

'

'

'

'

'

'

'

'

1.6

Net income attributable to Koppers

65.6

'

'

'

65.6

'

'

'

'

'

'

'

'

Reclassification of unrecognized pension prior service cost to expense, net of tax expense of $0.1, $0.0 and $0.0

'

'

'

'

'

'

'

'

0

'

'

'

'

Reclassification of unrecognized pension net loss to expense, net of tax expense of $2.8, $3.1 and $2.4

'

'

'

'

'

'

'

'

'

5.3

'

'

'

Employee stock plans

'

'

'

10.4

'

'

'

'

'

'

'

'

'

Change in foreign currency transactions of long-term subsidiary investments

'

'

'

'

'

'

1.8

'

'

'

'

'

'

Reclassification of unrecognized pension transition asset to expense, net of tax benefit of $0.0, $0.1 and $0.1

-0.3

'

'

'

'

'

'

-0.3

'

'

'

'

'

Purchases

'

'

'

'

'

'

'

'

'

'

-8.1

'

'

Investment in noncontrolling interests

'

'

'

'

'

'

'

'

'

'

'

'

3.3

Common Stock dividends

'

'

'

'

-20.3

'

'

'

'

'

'

'

'

Revaluation of unrecognized pension prior service cost, net of tax expense of $0.6, $0.0 and $0.0

'

'

'

'

'

'

'

'

0

'

'

'

'

Revaluation of unrecognized pension net loss, net of tax expense (benefit) of $10.0, $(0.9) and $(11.7)

'

'

'

'

'

'

'

'

'

-2.5

'

'

'

Currency translation adjustment

'

'

'

'

'

'

'

'

'

'

'

'

0.2

Total equity - end of year

168.1

'

'

'

'

'

'

'

'

'

'

'

'

Balance at Dec. 31, 2012

150.6

0

0.2

153.3

52

-22

34.5

0

-0.2

-56.3

-32.9

150.6

17.5

Change in currency translation adjustment excluding foreign currency transactions of long-term subsidiary investments

-0.6

'

'

'

'

-1.1

'

'

'

'

'

'

'

Net income (loss) attributable to noncontrolling interests

-0.3

'

'

'

'

'

'

'

'

'

'

'

-0.3

Net income attributable to Koppers

40.4

'

'

'

40.4

'

'

'

'

'

'

'

'

Reclassification of unrecognized pension prior service cost to expense, net of tax expense of $0.1, $0.0 and $0.0

'

'

'

'

'

'

'

'

0.1

'

'

'

'

Reclassification of unrecognized pension net loss to expense, net of tax expense of $2.8, $3.1 and $2.4

'

'

'

'

'

'

'

'

'

4.7

'

'

'

Employee stock plans

'

'

'

5.6

'

'

'

'

'

'

'

'

'

Change in foreign currency transactions of long-term subsidiary investments

'

'

'

'

'

'

-9.4

'

'

'

'

'

'

Reclassification of unrecognized pension transition asset to expense, net of tax benefit of $0.0, $0.1 and $0.1

0

'

'

'

'

'

'

0

'

'

'

'

'

Purchases

'

'

'

'

'

'

'

'

'

'

-17.5

'

'

Investment in noncontrolling interests

'

'

'

'

'

'

'

'

'

'

'

'

2.3

Common Stock dividends

'

'

'

'

-21.1

'

'

'

'

'

'

'

'

Revaluation of unrecognized pension prior service cost, net of tax expense of $0.6, $0.0 and $0.0

'

'

'

'

'

'

'

'

0.9

'

'

'

'

Revaluation of unrecognized pension net loss, net of tax expense (benefit) of $10.0, $(0.9) and $(11.7)

'

'

'

'

'

'

'

'

'

16.6

'

'

'

Currency translation adjustment

'

'

'

'

'

'

'

'

'

'

'

'

0.5

Total equity - end of year

189.8

'

'

'

'

'

'

'

'

'

'

'

'

Balance at Dec. 31, 2013

$169.80

'

'

$158.90

$71.30

($10.20)

$24

$0

$0.80

($35)

($50.40)

$169.80

$20

Consolidated_Statement_of_Shar1

Consolidated Statement of Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Unrecognized pension transition asset, tax amount	$0	$0.10	$0.10
Unrecognized Pension Transition Asset [Member] | Accumulated Other Comprehensive Loss [Member]	'	'	'
Unrecognized pension transition asset, tax amount	0	0.1	0.1
Unrecognized Pension Prior Service Cost [Member] | Accumulated Other Comprehensive Loss [Member]	'	'	'
Reclassification of unrecognized pension prior service cost, tax expense	0.1	0	0
Revaluation of unrecognized pension prior service cost, tax expense	0.6	0	0
Unrecognized Pension Net Loss [Member] | Accumulated Other Comprehensive Loss [Member]	'	'	'
Reclassification of unrecognized pension net loss, tax expense	2.8	3.1	2.4
Revaluation of unrecognized pension net loss, tax expense (benefit)	$10	($0.90)	($11.70)

Description_of_Business

Description of Business	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Description of Business	'
	1. Description of Business
	Parent company of Koppers Inc. – In these financial statements, unless otherwise indicated or the context requires otherwise, when the terms “Koppers,” the “Company,” “we,” “our” or “us,” are used, they mean Koppers Holdings Inc. (“Koppers Holdings”) and its subsidiaries on a consolidated basis. The use of these terms is not intended to imply that Koppers Holdings and Koppers Inc. are not separate and distinct legal entities from each other and from their respective subsidiaries. Koppers Holdings has no direct operations and no significant assets other than the stock of Koppers Inc. It depends on the dividends from the earnings of Koppers Inc. and its subsidiaries to generate the funds necessary to meet its financial obligations. The terms of Koppers Inc.’s revolving credit facility prohibit Koppers Inc. from paying dividends and otherwise transferring assets except for certain limited dividends. Further, the terms of the indenture governing Koppers Inc.’s Senior Notes significantly restrict Koppers Inc. from paying dividends and otherwise transferring assets to Koppers Holdings.
	Business description – The Company is a global integrated producer of carbon compounds and treated and untreated wood products and services for use in a variety of markets including the aluminum, railroad, specialty chemical, utility, concrete and steel industries. The Company’s business is operated through two business segments, Carbon Materials and Chemicals and Railroad and Utility Products and Services.
	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, rail joint bars and services primarily to the railroad industry and treated wood products to the utility industry. Railroad products include procuring and treating items such as crossties, switch ties and various types of lumber used for railroad bridges and crossings and the manufacture of rail joint bars. Utility products include transmission and distribution poles and pilings. The segment also produces concrete crossties through a joint venture.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	2. Summary of Significant Accounting Policies
	Basis of presentation – The consolidated financial statements include the accounts of the Company and all majority-owned subsidiaries for which the Company is deemed to exercise control over its operations. All significant intercompany transactions have been eliminated in consolidation. The Company’s investments in 20 percent to 50 percent-owned companies in which it has the ability to exercise significant influence over operating and financial policies are accounted for using the equity method of accounting. Accordingly, the Company’s share of the earnings of these companies is included in the accompanying consolidated statement of income. Certain prior period amounts in the consolidated financial statements and notes thereto have been reclassified to conform to the current period’s presentation.
	Use of estimates – Accounting principles generally accepted in the U.S. require management to make estimates and judgments that affect the reported amounts of assets and liabilities and the disclosure of contingencies on the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Estimates have been prepared on the basis of the most current and best available information and actual results could differ materially from these estimates.
	Foreign currency translation – For consolidated entities outside of the U.S. that prepare financial statements in currencies other than the U.S. dollar, results of operations and cash flows are translated at average exchange rates during the period, and asset and liabilities are translated at end-of-period exchange rates. Cumulative translation adjustments are included as a separate component of accumulated other comprehensive loss in shareholders’ equity.
	Foreign currency transaction gains and losses result from transactions denominated in a currency which is different than the currency used by the entity to prepare its financial statements. Foreign currency transaction losses were $0.5 million, $1.7 million and $0.5 million for the years ended December 31, 2013, 2012 and 2011, respectively.
	Revenue recognition – The Company recognizes revenue when the risks and rewards of ownership and title to the product have transferred to the customer. Revenue recognition generally occurs at the point of shipment; however in certain circumstances as shipping terms dictate, revenue is recognized at the point of destination. Shipping and handling costs are included as a component of cost of sales.
	The Company recognizes revenue related to the procurement of certain untreated railroad crossties upon transfer of title to the customer, which occurs upon delivery to the Company’s plant and acceptance by the customer. Service revenue, consisting primarily of wood treating services, is recognized at the time the service is provided. Payment on sales of untreated railroad crossties and wood treating services are generally due within 30 days of the invoice date. The Company’s recognition of revenue with respect to untreated crossties meets all the recognition criteria of Securities and Exchange Commission Staff Accounting Bulletin Topic 13.A.3., including transfer of title and risk of ownership, the existence of fixed purchase commitments and delivery schedules established by the customer, and the completion of all performance obligations by the Company. Revenue recognized for untreated crosstie sales for the years ended December 31, 2013, 2012 and 2011 amounted to $108.3 million, $109.0 million and $116.5 million, respectively.
	Research & development – Research and development costs are expensed as incurred and are included in selling, general and administrative expenses. These costs totaled $2.4 million in 2013, $2.3 million in 2012 and $1.9 million in 2011.
	Cash and cash equivalents – Cash and cash equivalents include cash on hand and on deposit and investments in highly liquid investments with an original maturity of 90 days or less.
	Accounts receivable – The Company maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments. In circumstances where the Company becomes aware of a specific customer’s inability to meet its financial obligations to Koppers, a specific reserve for bad debts is recorded against amounts due. If the financial condition of the Company’s customers were to deteriorate, resulting in an inability to make payments, additional allowances may be required.
	Inventories – Inventories are carried at lower of cost or market on a worldwide basis. In the U.S., inventory cost (excluding miscellaneous types of inventory) is determined primarily utilizing the last-in, first-out (“LIFO”) basis. Inventory cost outside the U.S. is determined utilizing the first-in, first-out (“FIFO”) basis. Market represents replacement cost for raw materials and net realizable value for work in process and finished goods. LIFO inventories constituted approximately 62 percent of the FIFO inventory value at December 31, 2013 and 2012.
	Property, plant & equipment – Property, plant and equipment are recorded at purchased cost and include improvements which significantly increase capacities or extend useful lives of existing plant and equipment. Depreciation expense is calculated by applying the straight-line method over estimated useful lives. Estimated useful lives for buildings generally range from 10 to 20 years and depreciable lives for machinery and equipment generally range from 3 to 10 years. Net gains and losses related to asset disposals are recognized in earnings in the period in which the disposal occurs. Routine repairs, replacements and maintenance are expensed as incurred.
	The Company periodically evaluates whether current facts and circumstances indicate that the carrying value of its depreciable long-lived assets may not be recoverable. If an asset, or logical grouping of assets, is determined to be impaired, the asset is written down to its fair value using discounted future cash flows and, if available, quoted market prices.
	Goodwill & other intangible assets – Goodwill and other purchased intangible assets are included in the identifiable assets of the business segment to which they have been assigned. The Company performs impairment tests annually for goodwill, and more often as circumstances require. When it is determined that impairment has occurred, an appropriate charge to earnings is recorded. The Company performed its annual impairment test in the fourth quarters of 2013 and 2012 and determined that the estimated fair values substantially exceeded the carrying values of all the reporting units and accordingly, there was no impairment of goodwill.
	Identifiable intangible assets, other than goodwill, are recorded at cost. Identifiable intangible assets that do not have indefinite lives are amortized on a straight-line basis over their estimated useful lives.
	Deferred income taxes – Deferred tax assets and liabilities are recognized for future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. The effect on deferred tax assets and liabilities of a change in tax laws is recognized in earnings in the period the new laws are enacted. A valuation allowance is recorded to reduce the carrying amounts of deferred tax assets unless it is more likely than not that such assets will be realized. Deferred tax liabilities have not been recognized for the undistributed earnings of certain foreign subsidiaries because management intends to permanently reinvest such earnings in foreign operations.
	Self-insured liabilities – The Company is self-insured for property, casualty and workers’ compensation exposures up to various stop-loss coverage amounts. Losses are accrued based upon the Company’s estimates of the liability for the related deductibles of claims incurred. Such estimates utilize actuarial methods based on various assumptions, which include but are not limited to, the Company’s historical loss experience and projected loss development factors. In 2013 and 2012, reversals of self-insured liabilities occurred as a result of favorable loss trends related to self-insured claims.
		2013			2012
	(Dollars in millions)
	Self-insured liabilities at beginning of year	$	7.6		$	7.4
	Expense		2.5			2.4
	Reversal of self-insured liabilities		(0.4	)		(1.0	)
	Cash expenditures		(1.3	)		(1.2	)
	Self-insured liabilities at end of year	$	8.4		$	7.6
	Derivative financial instruments – The Company uses forward exchange contracts to hedge exposure to currency exchange rate changes on transactions and other commitments denominated in a foreign currency. Contracts are generally written on a short-term basis and are not held for trading or speculative purposes. The Company recognizes the fair value of the forward contracts as an asset or liability at each reporting date. Because the Company has not elected to designate the forward exchange contracts for hedge accounting treatment, changes in the fair value of the forward exchange contracts are recognized immediately in earnings.
	Asset retirement obligations – Asset retirement obligations are initially recorded at fair value and are capitalized as part of the cost of the related long-lived asset when sufficient information is available to estimate fair value. The capitalized costs are subsequently charged to depreciation expense over the estimated useful life of the related long-lived asset. The fair value of the obligation is determined by calculating the discounted value of expected future cash flows and accretion expense is recorded each month to ultimately increase this obligation to full value.
	The Company recognizes asset retirement obligations for the removal and disposal of residues; dismantling of certain tanks required by governmental authorities; cleaning and dismantling costs for owned rail cars; cleaning costs for leased rail cars and barges; and site demolition.
	The following table describes changes to the Company’s asset retirement obligation liabilities at December 31, 2013 and 2012:
		2013			2012
	(Dollars in millions)
	Asset retirement obligation at beginning of year	$	21.5		$	21.3
	Accretion expense		1.2			1.1
	Revision in estimated cash flows		6.7			1.8
	Cash expenditures		(5.6	)		(3.0	)
	Currency translation		(0.6	)		0.3
	Asset retirement obligation at end of year	$	23.2		$	21.5
	Litigation & contingencies – Amounts associated with litigation and contingencies are accrued when management, after taking into consideration the facts and circumstances of each matter including any settlement offers, has determined that it is probable that a liability has been incurred and the amount of loss can be reasonably estimated. Legal costs for litigation are expensed as incurred with the exception of legal fees relating the CERCLA sites.
	Other current assets – Included in other current assets are prepaid expenses totaling $17.3 million and $7.4 million at December 31, 2013 and 2012, respectively.
	Environmental liabilities – The Company accrues for remediation costs and penalties when the responsibility to remediate is probable and the amount of related cost is reasonably estimable. If only a range of potential liability can be estimated and no amount within the range is more probable than another, the accrual is recorded at the low end of that range. Remediation liabilities are discounted if the amount and timing of the cash disbursements are readily determinable.
	Deferred revenue 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 describes changes to the Company’s deferred revenue at December 31, 2013 and 2012:
		2013			2012
	(Dollars in millions)
	Deferred revenue at beginning of year	$	3.9		$	4.8
	Revenue earned		(0.7	)		(0.9	)
	Deferred revenue at end of year	$	3.2		$	3.9
	Stock-based compensation – The Company records compensation cost over the vesting period for share-based payments to employees at an amount equivalent to the grant date fair value of the stock award. No compensation cost is recognized for any stock awards that are forfeited in the event the recipient fails to meet the vesting requirements.

Business_Acquisitions

Business Acquisitions	12 Months Ended
	Dec. 31, 2013
Business Combinations [Abstract]	'
Business Acquisitions	'
	3. Business Acquisitions
	Western Poles – On November 19, 2012, the Company acquired the pole distribution business (“Western Poles”) of Ridolfo Forestry Products Pty Limited for cash of $13.8 million and expected future payments totaling $4.9 million (on a discounted basis) to be paid over a period of 36 months assuming certain sales contracts remain in effect. The Western Poles business mainly serves utility customers in Western Australia and complements our existing wood treatment business in Australia. The business is part of the Railroad and Utility Products and Services segment.
	Pro-forma information – The consolidated pro forma results of operations if the acquisition had been completed as of the beginning of the year in 2012 would have been pro forma revenue of $1,581.7 million and operating profit of $130.1 million for the year ended December 31, 2012. The consolidated pro forma results of operations if the acquisition had been completed as of the beginning of the year in 2011 would have been pro forma revenue of $1,480.3 million and operating profit of $123.7 million for the year ended December 31, 2011.
	Subsequent event – 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, after an adjustment for working capital of approximately $0.8 million, was $29.6 million subject to post-closing adjustments. The purchase has been funded primarily by available cash. The business is part of the Railroad and Utility Products and Services segment.

Discontinued_Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2013
Discontinued Operations And Disposal Groups [Abstract]	'
Discontinued Operations	'
	4. Discontinued Operations
	In December 2011, the Company ceased manufacturing operations at its carbon black facility located in Kurnell, Australia. This decision was made as a result of deteriorating business conditions including raw material availability and cost, competition in the export markets due to the strength of the Australian dollar and a variety of other factors. The costs related to this closure totaled $41.0 million in the fourth quarter of 2011. The Company estimates that total future closure costs related to this facility will be approximately $0.5 million. The closure is expected to be completed during 2015. The results of operations of the carbon black facility have been reclassified to discontinued operations for all periods presented as run-off activities were completed in the first quarter of 2012. The facility is part of the Carbon Materials and Chemicals segment. Net sales from this discontinued operation totaled $5.6 million and $72.7 million for the years ended December 31, 2012 and 2011, respectively. Operating loss from this discontinued operation totaled $(0.2) million, $(0.3) million and $(43.7) million for the years ended December 31, 2013, 2012 and 2011, respectively.
	Details of the restructuring activities and related reserves for 2013 and 2012 are as follows:
		Severance		Environmental			Inventory			Site			Other			Total
		and		remediation			writedowns			demolition
		employee
		benefits
	(Dollars in millions)
	Reserve at January 1, 2012	$	1.8	$	6.7		$	0		$	6.2		$	1.2		$	15.9
	Charges		0.1		0			0.4			0			0			0.5
	Costs charged against assets		0		0			(0.4	)		0			0			(0.4	)
	Reversal of accrued charges		0		0			0			0			(0.6	)		(0.6	)
	Cash paid		-1.7		(0.1	)		0			(0.4	)		(0.5	)		(2.7	)
	Currency translation		0		0.1			0			0.1			0			0.2
	Reserve at December 31, 2012	$	0.2	$	6.7		$	0		$	5.9		$	0.1		$	12.9
	Reversal of accrued charges		-0.1		0			0			(0.3	)		0			(0.4	)
	Cash paid		0		(0.1	)		0			(2.0	)		(0.1	)		(2.2	)
	Currency translation		0		(1.0	)		0			(0.7	)		0			(1.7	)
	Reserve at December 31, 2013		$0.10	$	5.6		$	0		$	2.9		$	0		$	8.6

Earnings_and_Dividends_per_Com

Earnings and Dividends per Common Share	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Earnings and Dividends per Common Share	'
	5. Earnings and Dividends 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 nonvested 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 and performance restricted stock units that have not met vesting criteria are 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:
		Year Ended December 31,
		2013			2012			2011
	(Dollars in millions, except share amounts, in thousands, and per share amounts)
	Net income attributable to Koppers	$	40.4		$	65.6		$	36.9
	Less: discontinued operations		(0.1	)		(0.1	)		(19.9	)
	Income from continuing operations attributable to Koppers	$	40.5		$	65.7		$	56.8
	Weighted average common shares outstanding:
	Basic		20,575			20,681			20,599
	Effect of dilutive securities		240			246			234
	Diluted		20,815			20,927			20,833
	Earnings per common share – continuing operations:
	Basic earnings per common share	$	1.96		$	3.18		$	2.75
	Diluted earnings per common share		1.94			3.14			2.72
	Other data:
	Antidilutive securities excluded from computation of diluted earnings per common share		240			194			106
	On February 5, 2014, the board of directors declared a quarterly dividend of 25 cents per common share, payable on April 7, 2014 to shareholders of record as of February 18, 2014.

Stockbased_Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Stock-based Compensation	'
	6. Stock-based Compensation
	The amended and restated 2005 Long-Term Incentive Plan (the “LTIP”) provides for the grant to eligible persons of stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance awards, dividend equivalents and other stock-based awards, which are collectively referred to as the awards.
	Under the LTIP, the board of directors granted restricted stock units and performance stock units to certain employee participants (collectively, the “stock units”) each year starting in 2007. The restricted stock units vest on the third anniversary of the grant date, 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 December 31, 2013:
	Performance Period	Minimum				Target				Maximum
		Shares				Shares				Shares
	2012 – 2014		0				95,956				143,934
	2013 – 2015		0				93,523				140,285
	The following table shows a summary of the status and activity of non-vested stock awards for the year ended December 31, 2013:
		Restricted				Performance				Total				Weighted Average
		Stock Units				Stock Units				Stock Units				Grant Date Fair
														Value per Unit
	Non-vested at January 1, 2013		136,098				268,677				404,775			$	36.11
	Granted		62,276				97,318				159,594			$	42.64
	Credited from dividends		3,526				7,064				10,590			$	35.17
	Performance stock unit adjustment		0				43,921				43,921			$	40.09
	Vested		(46,314	)			(85,798	)			(132,112	)		$	29.81
	Forfeited		(6,750	)			(11,198	)			(17,948	)		$	40.26
	Non-vested at December 31, 2013		148,836				319,984				468,820			$	40.3
	Stock options to most executive officers vest and become exercisable upon the completion of a three-year service period which commences on the grant date. The stock options have a term of 10 years. In the event of termination of employment, other than retirement, death or disability, any non-vested options are forfeited for most participants. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the options over the service period will result for most participants. There are special vesting provisions for the stock options related to a change in control.
	In accordance with accounting standards, compensation expense for non-vested stock options is recorded over the vesting period based on the fair value at the date of grant. The fair value of stock options on the date of grant is calculated using the Black-Scholes-Merton model and the assumptions listed below:
				February 2013 Grant				February 2012 Grant				February 2011 Grant
	Grant date price per share of option award			$	42.76			$	38.21			$	40.26
	Expected dividend yield per share				2.75	%			2.75	%			2.5	%
	Expected life in years				6.5				6.5				6.5
	Expected volatility				53.77	%			55.06	%			60	%
	Risk-free interest rate				1.29	%			1.34	%			3.02	%
	Grant date fair value per share of option awards			$	17.28			$	15.82			$	19.28
	The dividend yield is based on the Company’s current and prospective dividend rate which calculates a continuous dividend yield based upon the market price of the underlying common stock. The expected life in years is based on the simplified method permitted under Securities and Exchange Commission Staff Accounting Bulletin No. 14d.2 which calculates the average of the weighted vesting term and the contractual term of the option. This method was selected due to the lack of historical exercise data with respect to the Company. Expected volatility is based on the historical volatility of the Company’s common stock and the historical volatility of certain other similar public companies. The risk-free interest rate is based on U.S. Treasury bill rates for the expected life of the option.
	The following table shows a summary of the status and activity of stock options for the year ended December 31, 2013:
		Options				Weighted Average				Weighted Average				Aggregate Intrinsic
						Exercise Price				Remaining				Value (in millions)
						per Option				Contractual Term
										(in years)
	Outstanding at January 1, 2013		331,799			$	34.07
	Granted		94,532			$	42.76
	Exercised		(5,251	)		$	39.04
	Outstanding at December 31, 2013		421,080			$	35.96				6.86			$	4.1
	Exercisable at December 31, 2013		167,565			$	29.15				4.7			$	2.8
	Total stock-based compensation expense recognized for the three years ended December 31, 2013 is as follows:
		Year Ended December 31,
		2013				2012				2011
	(Dollars in millions)
	Stock-based compensation expense recognized:
	Selling, general and administrative expenses	$	4.3			$	6.9			$	5.3
	Less related income tax benefit		1.7				2.8				2
	Decrease in net income attributable to Koppers	$	2.6			$	4.1			$	3.3
	As of December 31, 2013 total future compensation expense related to non-vested stock-based compensation arrangements totaled $4.0 million and the weighted-average period over which this expense is expected to be recognized is approximately 19 months.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	7. Income Taxes
	Income Tax Provision
	Components of the Company’s income tax provision from continuing operations are as follows:
		Years Ended December 31,
		2013			2012			2011
	(Dollars in millions)
	Current:
	Federal	$	3.5		$	15.7		$	24.7
	State		0.6			1.3			1.1
	Foreign		14			8.6			21.5
	Total current tax provision		18.1			25.6			47.3
	Deferred:
	Federal		16.4			4.9			(6.7	)
	State		2.5			(1.2	)		0.1
	Foreign		(0.2	)		4			(2.0	)
	Total deferred tax provision (benefit)		18.7			7.7			(8.6	)
	Total income tax provision	$	36.8		$	33.3		$	38.7
	Income before income taxes for 2013, 2012 and 2011 included $24.6 million, $42.6 million and $51.8 million, respectively, from foreign operations.
	The provision for income taxes is reconciled with the federal statutory rate as follows:
		Years Ended December 31,
		2013			2012			2011
	Federal income tax rate		35	%		35	%		35	%
	State income taxes, net of federal tax benefit		2.1			(0.5	)		0.7
	Foreign earnings taxed at different rates		15.5			0.5			1.4
	Domestic production activities deduction		(2.0	)		(2.7	)		(1.3	)
	Non-deductible fines and penalties		0			0			0.2
	Deferred tax adjustments		(0.2	)		(0.3	)		0.1
	Change in tax contingency reserves		(1.5	)		1.2			3.8
	Foreign tax credits		(1.1	)		(0.6	)		0
	Other		0			0.5			0.3
			47.8	%		33.1	%		40.2	%
	The Company has not provided any U.S. tax on undistributed earnings of foreign subsidiaries or joint ventures that are reinvested indefinitely. At December 31, 2013 consolidated retained earnings of the Company included approximately $103 million of undistributed earnings, which are permanently invested, from these foreign entities. It is not practical at this time, however, to estimate the amount of taxes that may be payable on the distribution of these earnings.
	Taxes Excluded from Net Income Attributable to Koppers
	The amount of income tax provision (benefit) included in comprehensive income but excluded from net income attributable to Koppers relating to adjustments to reflect the unfunded status of employee post-retirement benefit plans is $13.5 million, $2.2 million and $(9.3) million for the years ended December 31, 2013, 2012 and 2011, respectively.
	The amount of income tax benefit included in shareholders’ equity but excluded from net income attributable to Koppers relating to the expense for restricted stock and employee stock options recognized differently for financial and tax reporting purposes was $0.5 million for the year ended December 31, 2013 and $1.6 million for the year ended December 31, 2012.
	Deferred Tax Assets and Liabilities
	Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes.
	Significant components of the Company’s deferred tax assets and liabilities are as follows:
		December 31,
		2013			2012
	(Dollars in millions)
	Deferred tax assets:
	Reserves, including insurance, environmental and deferred revenue	$	16.5		$	19.8
	Pension and other postretirement benefits obligations		10.3			33.4
	Tax credits		10.3			9.6
	Net operating loss benefit		10			9.4
	Accrued employee compensation		9.4			9.8
	Asset retirement obligations		6.8			7.2
	Book/tax inventory accounting differences		3.3			3
	Capital loss benefit		1.1			1.5
	Other		2.2			3.1
	Valuation allowance		(19.7	)		(17.4	)
	Total deferred tax assets		50.2			79.4
	Deferred tax liabilities:
	Tax over book depreciation and amortization		34.1			29.5
	Unremitted earnings of foreign subsidiaries		6.8			5.9
	Tax/book inventory accounting differences		1.1			1.1
	Other		3.7			3.7
	Total deferred tax liabilities		45.7			40.2
	Net deferred tax assets	$	4.5		$	39.2
	A valuation allowance is provided when it is more likely than not that some portion or all of the deferred tax assets will not be realized. At December 31, 2013, the Company has recorded a valuation allowance of $7.2 million for certain state net operating loss carryforwards anticipated to produce no tax benefit. The Company has recorded a valuation allowance of $9.4 million for certain foreign tax credits in the United States expected to produce no benefit. These foreign tax credits will begin to expire in 2018. The Company has recorded a valuation allowance of $1.7 million for foreign net operating losses and certain foreign temporary differences that most likely will not be deducted. Additionally, the Company has recorded a valuation allowance of $1.1 million for certain capital loss carryforwards in Australia expected to produce no benefit. The Company has tax-effected state net operating losses of $9.1 million, which will expire from 2015 to 2032 and tax-effected foreign net operating losses of $0.9 million, which will expire in 2019.
	Uncertain Tax Positions
	The Company or one of its subsidiaries files income tax returns in 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 December 31, 2013 and 2012, the total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate, was approximately $4.5 million and $5.5 million, respectively. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:
	December 31,
	2013			2012			2011
(Dollars in millions)
Balance at beginning of year	$	7.7		$	9.9		$	6.5
Additions based on tax provisions related to the current year		0.4			0.5			4
Additions for tax provisions of prior years		0.4			1.3			0
Reductions of tax provisions of prior years		(0.8	)		(0.5	)		0
Reductions as a result of payments and settlements		(1.1	)		(2.8	)		0
Reductions as a result of a lapse of the applicable statute of limitations		(0.5	)		(0.7	)		(0.6	)
Balance at end of year	$	6.1		$	7.7		$	9.9
The Company recognizes interest expense or interest income and any related penalties from uncertain tax positions in income tax expense. For each year ended December 31, 2013, 2012 and 2011, the Company recognized ($0.1) million, $0.3 million and $0.2 million, respectively, in interest and penalties. As of December 31, 2013 and 2012, the Company had accrued approximately $1.2 million and $1.3 million for interest and penalties, respectively.
Recently-Enacted Tax Regulations
On September 13, 2013, Treasury and the Internal Revenue Service issued final regulations regarding the deduction and capitalization of expenditures related to tangible property. The final regulations under Internal Revenue Code Sections 162, 167 and 263(a) apply to amounts paid to acquire, produce, or improve tangible property as well as dispositions of such property and are generally effective for tax years beginning on or after January 1, 2014. We have evaluated these regulations and determined they do not have a material impact on our consolidated results of operations, cash flows or financial position.

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Segment Information	'
	8. Segment Information
	The Company has two reportable segments: Carbon Materials and Chemicals and Railroad and Utility Products and Services. The Company’s reportable segments contain business units that offer different products. The reportable segments are each managed separately because they manufacture and distribute distinct products with different production processes. The business units have been aggregated into two reportable segments since management believes the long-term financial performance of these business units is affected by similar economic conditions.
	The Company’s Carbon Materials and Chemicals segment is primarily a manufacturer of carbon pitch, naphthalene, phthalic anhydride, creosote and carbon black feedstock. Carbon pitch is a critical raw material used in the production of aluminum and for the production of steel in electric arc furnaces. Naphthalene is used for the production of phthalic anhydride and as a surfactant in the production of concrete. Phthalic anhydride is used in the production of plasticizers, polyester resins and alkyd paints. Creosote is used in the treatment of wood and carbon black feedstock is used in the production of carbon black.
	The Company’s Railroad and Utility Products and Services segment sells treated and untreated wood products, manufactured products and services primarily to the railroad and public utility markets. Railroad products include procuring and treating items such as crossties, switch ties and various types of lumber used for railroad bridges and crossings and the manufacture of rail joint bars. Utility products include transmission and distribution poles and pilings.
	The Company evaluates performance and determines resource allocations based on a number of factors, the primary measure being operating profit or loss from operations. Operating profit does not include equity in earnings of affiliates, other income, interest expense or income taxes. Operating profit also excludes the operating costs of Koppers Holdings Inc., the parent company of Koppers Inc. The accounting policies of the reportable segments are the same as those described in the summary of significant accounting policies. Intersegment transactions are eliminated in consolidation.
	Results of Segment Operations
			Year Ended December 31,
			2013			2012			2011
	(Dollars in millions)
	Revenues from external customers:
	Carbon Materials and Chemicals		$	906.1		$	999.7		$	943.1
	Railroad and Utility Products and Services			572.2			555.3			523.1
	Total		$	1,478.30		$	1,555.00		$	1,466.20
	Intersegment revenues:
	Carbon Materials and Chemicals		$	94.2		$	106.5		$	95.2
	Depreciation & amortization(a):
	Carbon Materials and Chemicals		$	18.2		$	16.9		$	17.4
	Railroad and Utility Products and Services			11.5			10.7			9.5
	Total		$	29.7		$	27.6		$	26.9
	Operating profit:
	Carbon Materials and Chemicals		$	43.9		$	83.1		$	89.1
	Railroad and Utility Products and Services			58.3			45.1			34.8
	Corporate(b)			(1.9	)		(1.6	)		(1.2	)
	Total		$	100.3		$	126.6		$	122.7
	Capital expenditures (including acquisitions):
	Carbon Materials and Chemicals		$	58		$	17.3		$	23
	Railroad and Utility Products and Services			15.9			25			10.2
	Corporate			1.3			0.6			0.6
	Total		$	75.2		$	42.9		$	33.8
	(a)	Excludes impairment charges of $11.9 million in 2013 for Carbon Materials and Chemicals and $0.6 million in 2012 for Railroad and Utility Products and Services.
	(b)	Operating loss for Corporate includes general and administrative costs for Koppers Holdings Inc, the parent company of Koppers Inc.
	Assets and Goodwill by Segment
			December 31,
			2013			2012
	(Dollars in millions)
	Assets:
	Carbon Materials and Chemicals		$	535.5		$	516.3
	Railroad and Utility Products and Services			179.3			205
	Segment assets			714.8			721.3
	Cash & cash equivalents			30			4.8
	Income tax receivable			9			1.6
	Deferred taxes			13.3			35.5
	Deferred financing costs			7.2			7.2
	Property, plant and equipment, net			3.8			3.5
	Deferred charges			2.6			2.6
	Other			4.2			3.5
	Total		$	784.9		$	780
	Goodwill:
	Carbon Materials and Chemicals		$	68		$	70.2
	Railroad and Utility Products and Services			4.7			5.4
	Total		$	72.7		$	75.6
	Revenues and Long-lived Assets by Geographic Area
			Year			Revenue			Long-lived
									assets
	(Dollars in millions)
	United States			2013		$	782.5		$	169.1
				2012			827.6			162.9
				2011			787.5			161.6
	Australasia			2013			348.3			100.6
				2012			318.9			72.4
				2011			276.6			58.7
	Europe			2013			225.1			32.8
				2012			247.8			36.3
			2011			248			35.7
Other countries			2013			122.4			0
			2012			160.7			0
			2011			154.1			0
Total			2013		$	1,478.30		$	302.5
			2012		$	1,555.00		$	271.6
			2011		$	1,466.20		$	256
Revenues by geographic area in the above table are attributed by the destination country of the sale. Revenues from non-U.S. countries totaled $695.8 million in 2013, $727.4 million in 2012 and $681.1 million in 2011.
Segment Revenues for Significant Product Lines
		Year Ended December 31,
		2013			2012			2011
(Dollars in millions)
Carbon Materials and Chemicals:
Carbon pitch		$	384.7		$	442.4		$	431.1
Creosote and carbon black feedstock			228.2			233.8			162
Phthalic anhydride			98.6			120			112.4
Naphthalene			64.5			60.3			72.3
Other products			130.1			143.2			165.3
			906.1			999.7			943.1
Railroad and Utility Products and Services:
Railroad crossties			331.1			341.1			324.9
Utility poles			119.3			101.3			84.2
Creosote			61.4			57			52.7
Rail joint bars			24.5			25.6			24.7
Other products			35.9			30.3			36.6
			572.2			555.3			523.1
Total		$	1,478.30		$	1,555.00		$	1,466.20

Inventories

Inventories	12 Months Ended
	Dec. 31, 2013
Inventory Disclosure [Abstract]	'
Inventories	'
	9. Inventories
	Inventories as of December 31, 2013 and 2012 were as follows:
		December 31,
		2013		2012
	(Dollars in millions)
	Raw materials	$	105.4	$	118.2
	Work in process		19.2		20
	Finished goods		94.8		109.7
			219.4		247.9
	Less revaluation to LIFO		50.6		52.1
	Net	$	168.8	$	195.8
	For the years ended December 31, 2013 and 2011, liquidations of LIFO inventories increased operating profit by $0.2 million and $0.3 million.

Equity_Investments

Equity Investments	12 Months Ended
	Dec. 31, 2013
Equity Method Investments And Joint Ventures [Abstract]	'
Equity Investments	'
	10. Equity Investments
	The Company holds two investments in unconsolidated companies. KSA Limited Partnership is a 50 percent owned concrete crosstie operation located in Portsmouth, Ohio. Tangshan Koppers Kailuan Carbon Chemical Company Limited (“TKK”) is a 30-percent owned tar distillation facility in the Hebei Province of China. No dividends were paid for the three years ended December 31, 2013. Equity in earnings for the three years ended December 31, 2013 were as follows:
		Equity income
	(Dollars in millions)
	2013	$	0.8
	2012		0.8
	2011		0.2

Property_Plant_and_Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2013
Property Plant And Equipment [Abstract]	'
Property, Plant and Equipment	'
	11. Property, Plant and Equipment
	Property, plant and equipment as of December 31, 2013 and 2012 were as follows:
		December 31,
		2013		2012
	(Dollars in millions)
	Land	$	9.1	$	7
	Buildings		30.6		31.7
	Machinery and equipment		608.1		543.1
			647.8		581.8
	Less accumulated depreciation		450.8		420.7
	Net	$	197	$	161.1
	Depreciation expense, including impairment charges, for the years ended December 31, 2013, 2012 and 2011 amounted to $38.3 million, $25.2 million and $46.0 million, respectively.
	In connection with an acquisition prior to 2012, the Company had not reset gross carrying value and accumulated depreciation to zero for the acquired machinery and equipment and buildings. As a result the gross carrying value and corresponding accumulated depreciation amounts were both overstated by $78.2 million as of December 31, 2012. There was no impact on net book value for any period. The previously reported gross carrying value and accumulated depreciation amounts as of December 31, 2012 have been adjusted accordingly in the table contained in this note.
	Impairments – Impairment charges for 2013, 2012 and 2011 were $11.9 million, $0.6 million and $20.2 million, respectively. In 2013, impairment charges primarily related to the Carbon Material and Chemicals’ plants in Uithoorn, the Netherlands for $6.9 million, Tangshan, China for $4.0 million ($2.4 million, net of non-controlling interest) and a coal tar distillation plant in the United States for $0.7 million. This $0.7 million impairment charge was due to a change in production operations at the plant in late 2013. These impairment charges were calculated using a probability-weighted discounted cash flow model.
	The 2013 impairment of the Company’s plant in the Netherlands is due to the intended decision to discontinue coal tar distillation activities at the Uithoorn plant in July 2014. A final determination to discontinue production was made in January 2014 after consultation with and agreement on a severance plan with the plant’s works council and trade union, respectively. The remaining net book value of assets subject to impairment totals $1.8 million. This amount will be reflected in depreciation expense over the first six months of 2014 on an accelerated basis.
	The 2013 impairment of the Company’s 60-percent owned plant in Tangshan, China is due to the potential that the plant will be forced to cease production at some point as a result of Chinese government action. In October 2013, the Company was informed by the Tangshan Municipal People’s Government (“Tangshan Government”) of its intention to close the two coke batteries owned and operated by the Tangshan Iron and Steel Group Co., Ltd (“TISCO”) in Tangshan, China. The Tangshan Government has ordered the closure of these coke batteries by March 15, 2014 in an effort to improve the air quality in the Tangshan area. The Company’s 60-percent owned subsidiary, Koppers (China) Carbon & Chemical Company Limited (“KCCC”) is located within TISCO’s property and relies on its operations for a significant portion of raw material supply, utilities and other shared services. At the same time, the Tangshan Government has requested that KCCC consider the relocation of its operations and offered assistance to KCCC in this regard, although no specific details have been provided to the Company on the extent and nature of such assistance. Closure of the TISCO coke batteries would impact KCCC’s ability to operate its coal tar distillation plant on a long-term basis. The Company has entered discussions with its non-controlling partner in KCCC, TISCO, and the Tangshan Government to evaluate its options, which include remaining at the current location and continuing to operate or remaining at its current location on a temporary basis and transitioning to a new location.
	The closure or relocation of KCCC’s coal tar distillation facility would have a material adverse effect on the Company’s business, financial condition, cash flow and results of operations. For the most recent year ended December 31, 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 December 31, 2013, the remaining net book value of fixed assets subject to impairment was $8.1 million. This amount will be reflected in depreciation expense over the next three years on an accelerated basis reflecting management’s estimate of the remaining useful life of the assets.
	The Company believes it would be able to continue fulfilling current domestic Chinese customers and its export commitments with capacity at Koppers (Jiangsu) Carbon Chemical Company Limited, which is scheduled for production start-up in mid-2014, its other 30-percent owned Chinese company and other commercial relationships in China. However, the Company’s margin on export sales would be negatively affected due to its lower ownership interest in these companies.
	The charge in 2012 related to a Railroad and Utility Products and Services segment’s electricity co-generation plant in the United States. The charge in 2011 related to the Carbon Material and Chemicals segment’s carbon black facility in Australia.
	Port of Portland – In February 2012, approximately 400 tons of carbon pitch leaked from a storage tank at the Company’s terminal facility in Portland, Victoria, Australia. All of the coal tar pitch was contained within the tank farm area and was recovered. Insurance recoveries associated with the leak were a net $1.2 million for the year ended December 31, 2013. Costs directly associated with the leak were $2.5 million for the year ended December 31, 2012 and include inventory losses, emergency response expenses, incremental logistics costs, and material clean-up and removal expenses, net of insurance recoveries.

Goodwill_and_Other_Identifiabl

Goodwill and Other Identifiable Intangible Assets	12 Months Ended
	Dec. 31, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Goodwill and Other Identifiable Intangible Assets	'
	12. Goodwill and Other Identifiable Intangible Assets
	The change in the carrying amount of goodwill attributable to each business segment for the years ended December 31, 2013 and December 31, 2012 was as follows:
		Carbon Materials and			Railroad and			Total
		Chemicals			Utility Products
					and Services
	(Dollars in millions)
	Balance at December 31, 2011	$	69.4		$	2.7		$	72.1
	Acquisitions		0			2.6			2.6
	Currency translation		0.8			0.1			0.9
	Balance at December 31, 2012	$	70.2		$	5.4		$	75.6
	Currency translation		(2.2	)		(0.7	)		(2.9	)
	Balance at December 31, 2013	$	68		$	4.7		$	72.7
	The Company’s identifiable intangible assets with finite lives are being amortized over their estimated useful lives and are summarized below:
		December 31,
		2013									2012
		Gross			Accumulated			Net			Gross		Accumulated		Net
		Carrying			Amortization						Carrying		Amortization
		Amount									Amount
	(Dollars in millions)
	Customer contracts	$	19.8		$	9.7		$	10.1		$	20.9	$	8.1	$	12.8
	Supply contracts		2.9			1.1			1.8			2.8		0.8		2
	Non-compete agreements		1.6			1.3			0.3			1.7		1.2		0.5
	Favorable lease agreements		0.8			0.8			0			0.8		0.8		0
	Total	$	25.1		$	12.9		$	12.2		$	26.2	$	10.9	$	15.3
	In 2013, the gross carrying value of identifiable intangible assets decreased by $1.1 million due to foreign currency translation. The customer contracts have estimated useful lives of 10 to 15 years, the supply contracts have estimated useful lives of 10 years, the non-compete agreements have estimated useful lives of 3 to 12 years and the favorable lease agreements have estimated useful lives of 3 years. Total amortization expense related to these identifiable intangible assets was $2.1 million, $1.9 million and $1.5 million for the years ended December 31, 2013, 2012 and 2011, respectively. The weighted-average period for which identifiable intangible assets will be amortized is approximately 10.1 years. Estimated amortization expense for the next five years is summarized below:
		Estimated
		annual
		amortization
	(Dollars in millions)
	2014	$	1.8
	2015		1.8
	2016		1.3
	2017		1.1
	2018		1.1

Debt

Debt	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Debt	'
	13. Debt
	Debt at December 31, 2013 and December 31, 2012 was as follows:
							December 31,
		Weighted			Maturity		2013		2012
		Average
		Interest Rate
	(Dollars in millions, except interest rates)
	Revolving credit facility		0.00%			2018	$	0	$	0
	Construction loans		6.24%			2018		6.6		0
	Senior Notes		7 7/8%			2019		296.5		296.1
	Total debt							303.1		296.1
	Less short-term debt and current maturities of long-term debt							0		0
	Long-term debt (excluding current portion)						$	303.1	$	296.1
	Revolving Credit Facility
	The Koppers Inc. revolving credit facility agreement provides for a revolving credit facility of up to $350.0 million at variable rates. Borrowings under the revolving credit facility are secured by a first priority lien on substantially all of the assets of Koppers Inc. and its material domestic subsidiaries. The revolving credit facility contains certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends, investments or acquisitions. In addition, such covenants give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios. Commitment fees totaled $1.0 million in 2013, $1.0 million in 2012 and $1.1 million in 2011 and are charged to interest expense.
	As of December 31, 2013, the Company had $331.0 million of unused revolving credit availability for working capital purposes after restrictions from certain letter of credit commitments and other covenants. As of December 31, 2013, $19.0 million of commitments were utilized by outstanding letters of credit.
	Construction Loans
	On November 18, 2013, the Company’s 75-percent owned subsidiary, Koppers (Jiangsu) Carbon Chemical Company limited (“KJCC”) entered into two committed loan facility agreements for a combined commitment of RMB 265 million or approximately $44 million. The third party bank provided facility has a commitment amount of RMB 198.8 million and the other committed facility of RMB 66.2 million is provided by the 25-percent non-controlling shareholder in KJCC. Borrowings under the third party bank facility are secured by a letter of credit issued by a bank under the Company’s Revolving Credit Facility. The committed facilities will be used to finance the costs related to the construction of the coal tar distillation plant in Pizhou, Jiangsu province in China. The facilities are variable rate and have certain financial covenants that monitor minimum net worth and leverage. KJCC will repay the loans in six installments every six months starting in May 2016 with a final repayment on November 18, 2018, the maturity date of the loans.
	Senior Notes
	The Koppers Inc. 7 7/8 percent Senior Notes due 2019 (the “Senior Notes”) were issued on December 1, 2009 at an offering price of 98.311 percent of face value, or $294.9 million and have a principal amount at maturity of $300.0 million. The Senior Notes have an effective interest rate yield of 8  1/8 percent per annum. The Senior Notes are unsecured senior obligations that are fully and unconditionally guaranteed by Koppers Holdings and certain of Koppers Inc.’s wholly-owned domestic subsidiaries. The Senior Notes are structurally subordinated to indebtedness under the revolving credit facility.
	Interest on the Senior Notes is payable semiannually on December 1 and June 1 each year. On or after December 1, 2014, the Company is entitled to redeem all or a portion of the Senior Notes at a redemption price of 103.938 percent of principal value, declining annually in ratable amounts until the redemption price is equivalent to the principal value on December 1, 2017.
	The indenture governing the Senior Notes includes customary covenants that restrict, among other things, the ability of Koppers Inc. and its restricted subsidiaries to incur additional debt, pay dividends or make certain other restricted payments, incur liens, merge or sell all or substantially all of the assets of Koppers Inc. or its subsidiaries or enter into various transactions with affiliates.
	Debt Maturities and Deferred Financing Costs
	At December 31, 2013 the aggregate debt maturities for the next five years are as follows:
	(Dollars in millions)
	2014	$	0
	2015		0
	2016		1
	2017		2.3
	2018		3.3
	Thereafter		300
	Total maturities		306.6
	Future accretion on Senior Notes		(3.5	)
	Total debt	$	303.1
	Unamortized deferred financing costs (net of accumulated amortization of $5.9 million and $4.6 million at December 31, 2013 and 2012, respectively) were $7.2 million and $7.2 million at December 31, 2013 and 2012, respectively, and are included in other assets.

Leases

Leases	12 Months Ended
	Dec. 31, 2013
Leases [Abstract]	'
Leases	'
	14. Leases
	Future minimum commitments for operating leases having non-cancelable lease terms in excess of one year are as follows:
	(Dollars in millions)
	2014	$	37
	2015		21.2
	2016		16.4
	2017		14
	2018		12.3
	Thereafter		30
	Total	$	130.9
	Operating lease expense for 2013, 2012 and 2011 was $39.4 million, $44.3 million and $43.8 million, respectively.

Pensions_and_Postretirement_Be

Pensions and Post-retirement Benefit Plans	12 Months Ended
	Dec. 31, 2013
Compensation And Retirement Disclosure [Abstract]	'
Pensions and Post-retirement Benefit Plans	'
	15. Pensions and Post-retirement Benefit Plans
	The Company and its subsidiaries maintain a number of defined benefit and defined contribution plans to provide retirement benefits for employees in the U.S., as well as employees outside the U.S. These plans are maintained and contributions are made in accordance with the Employee Retirement Income Security Act of 1974 (“ERISA”), local statutory law or as determined by the board of directors. The defined benefit pension plans generally provide benefits based upon years of service and compensation. Pension plans are funded except for three domestic non-qualified defined benefit pension plans for certain key executives.
	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.
	Expense related to defined contribution plans totaled $5.3 million, $4.7 million and $4.8 million for the years ended December 31, 2013, 2012 and 2011, respectively. Expense related to contributions to multi-employer pension plans totaled $0.4 million, $0.4 million and $0.7 million for the years ended December 31, 2013, 2012 and 2011, respectively.
	Net periodic pension costs for 2013, 2012 and 2011 were as follows:
		December 31,
		Pension Benefits									Other Benefits
		2013			2012			2011			2013			2012		2011
	(Dollars in millions)
	Components of net periodic benefit cost:
	Service cost	$	3.4		$	3.5		$	3.3		$	0.1		$	0.1	$	0.2
	Interest cost		10.7			10.7			11.1			0.5			0.5		0.6
	Expected return on plan assets		(12.5	)		(10.7	)		(11.0	)		0			0		0
	Amortization of prior service cost		0.1			0.1			0.1			0			0		(0.1	)
	Amortization of net loss		7.6			8.1			6.3			(0.1	)		0		0
	Amortization of transition asset		0			(0.3	)		(0.3	)		0			0		0
	Settlements and curtailments		0.1			0.3			0.2			0			0		0
	Net periodic benefit cost	$	9.4		$	11.7		$	9.7		$	0.5		$	0.6	$	0.7
	Net periodic pension (credit) cost that is expected to be recognized from the amortization of prior service cost and net loss is estimated to total $(0.2) million and $3.8 million, respectively, for all plans in 2014.
	The change in the funded status of the pension and postretirement plans as of December 31, 2013 and December 31, 2012 is as follows:
		December 31,
		Pension Benefits						Other Benefits
		2013			2012			2013			2012
	(Dollars in millions)
	Change in benefit obligation:
	Benefit obligation at beginning of year	$	255.2		$	239.5		$	11.2		$	12.5
	Service cost		3.4			3.5			0.1			0.1
	Interest cost		10.7			10.7			0.5			0.5
	Plan participants’ contributions		0.2			0.2			0			0
	Actuarial (gains) losses		(18.6	)		10.3			(1.3	)		(1.8	)
	Plan amendments		(1.5	)		0			0			0
	Settlements		(0.9	)		(1.4	)		0			0
	Currency translation		0.2			2.4			0			0
	Benefits paid		(10.9	)		(10.0	)		(0.1	)		(0.1	)
	Benefit obligation at end of year		237.8			255.2			10.4			11.2
	Change in plan assets:
	Fair value of plan assets at beginning of year		175.6			146.6			0			0
	Actual return on plan assets		19.2			15.7			0			0
	Employer contribution		22.5			22.4			0.1			0.1
	Plan participants’ contributions		0.2			0.2			0			0
	Settlements		(0.9	)		(1.4	)		0			0
	Currency translation		0			2.1			0			0
	Benefits paid		(10.9	)		(10.0	)		(0.1	)		(0.1	)
	Fair value of plan assets at end of year		205.7			175.6			0			0
	Funded status of the plan	$	(32.1	)	$	(79.6	)	$	(10.4	)	$	(11.2	)
	Amounts recognized in the balance sheet consist of:
	Noncurrent assets	$	0.6		$	0.2		$	0		$	0
	Current liabilities		0.7			0.4			0.8			0.7
	Noncurrent liabilities		32			79.4			9.6			10.5
	Pension plans with benefit obligations in excess of plan assets:
	Benefit obligation	$	231.9		$	247.5
	Fair value of plan assets		199.2			167.6
	Pension plans with accumulated benefit obligations in excess of plan assets:
	Accumulated benefit obligation	$	225		$	229
	Fair value of plan assets		199.2			167.6
	The measurement date for all pension and postretirement assets and obligations is December 31 for each respective year.
	The accumulated benefit obligation for all defined benefit pension plans as of December 31, 2013 and 2012 was $230.6 million and $235.9 million, respectively.
	Expected Contributions for the 2014 Fiscal Year
	The expected contributions by the Company for 2014 are estimated to be $22.8 million for pension plans and $0.8 million for other benefit plans.
	Projected Benefit Payments
	Benefit payments for pension benefits, which are primarily funded by the pension plan assets, and other benefits, which are funded by general corporate assets and reflecting future expected service as appropriate, are expected to be paid as follows:
		Pension Benefits			Other Benefits
(Dollars in millions)
2014	$	11.2		$	0.8
2015		11.7			0.8
2016		12.6			0.8
2017		13.5			0.9
2018		14.5			0.9
2019 – 2023		74.5			4
Weighted-Average Assumptions as of December 31
	December 31,
	Pension Benefits						Other Benefits
	2013			2012			2013			2012
Discount rate		5.06	%		4.33	%		5.25	%		4.37	%
Expected return on plan assets		7.04			7.25
Rate of compensation increase		3.13			3.1
Initial medical trend rate								7.15			7.35
Basis for the Selection of the Long-Term Rate of Return on Assets
The long-term rate of return on assets assumption was determined by using the plan’s asset allocation as described in the plan’s investment policy and modeling a distribution of compound average returns over a time horizon. The model uses asset class return, variance, and correlation assumptions to produce the expected return. The return assumptions used forward looking gross returns influenced by the current bond yields, corporate bond spreads and equity risk premiums based on current market conditions.
In general, the long-term rate of return is the sum of the portion of total assets in each asset class multiplied by the expected return for that class, adjusted for expected expenses to be paid from the assets. To develop the expected long-term rate of return on assets assumption, the Company considered the historical returns and the future expectations for returns for each asset class, as well as the target asset allocation of the pension portfolio.
Investment Strategy
The weighted average asset allocation for the Company’s pension plans at December 31 by asset category is as follows:
	December 31,
	2013			2012
Equity securities		38	%		61	%
Debt securities		59			35
Other		3			4
		100	%		100	%
The Company’s investment strategy for its pension plans is to maintain an adequate level of diversification, to reduce interest rate and market risk and to provide adequate liquidity to meet immediate and future benefit payment requirements. The Company’s overall investment strategy is to achieve a mix of growth seeking assets, principally U.S. and international public company equity securities and income generating assets, principally debt securities, real estate and cash. Currently, the Company targets an allocation of 30 percent to 40 percent growth seeking assets and 60 percent to 70 percent income generating assets on an overall basis. The Company utilizes investment managers to assist in identifying and monitoring investments that meet these allocation criteria. With respect to the largest pension plan, the Company has implemented a strategy of reallocating pension assets from growth seeking assets to income generating assets as certain funded status levels are reached.
The investment valuation policy of the Company is to value investments at fair value. Most of the assets are invested in pooled or commingled investment vehicles. The Company’s interest in these investment vehicles is expressed as a unit of account with a value per unit that is the result of the accumulated values of the underlying investments. Equity securities held within these investment vehicles are typically priced on a daily basis using the closing market price from the exchange the security is traded. Debt securities held within these investment vehicles are typically priced on a daily basis by independent pricing services. The fair value of real estate investments are either priced through a listing on an exchange or are subject to periodic appraisals.
The pension assets are all substantially held in pooled or commingled investment vehicles. The following table sets forth by level, the Company’s pension plan assets at fair value, within the fair value hierarchy, as of December 31, 2013 and December 31, 2012:
	As of December 31, 2013
	Quoted prices			Significant			Significant			Total
	in active			observable			unobservable
	markets for			inputs			inputs
	identical assets			(Level 2)			(Level 3)
	(Level 1)
(Dollars in millions)
U.S. equity securities	$	17.8		$	15.9		$	0			$  33.7
International equity securities		0			44.3			0			44.3
U.S. debt securities		24.8			64.7			0			89.5
International debt securities		7.4			24.9			0			32.3
Real estate and other investments		0			1.5			0			1.5
Cash and cash equivalents		0			4.4			0			4.4
	$	50		$	155.7		$	0			$205.70
	As of December 31, 2012
	Quoted prices			Significant			Significant			Total
	in active			observable			unobservable
	markets for			inputs			inputs
	identical assets			(Level 2)			(Level 3)
	(Level 1)
(Dollars in millions)
U.S. equity securities	$	0		$	80		$	0			$  80.0
International equity securities		0			27.2			0			27.2
U.S. debt securities		0			36.4			0			36.4
International debt securities		0			24.5			0			24.5
Real estate and other investments		0			1.7			0			1.7
Cash and cash equivalents		0			5.8			0			5.8
	$	0		$	175.6		$	0			$175.60
Health Care Cost Trend Rates
The 2013 initial health care cost trend rate is assumed to be 7.35 percent and is assumed to decrease gradually to 4.5 percent in 2027 and remain at that level thereafter. The assumed health care cost trend rate has a significant effect on the amounts reported for other postretirement benefit liability. A one-percentage-point change in the assumed health care cost trend rate would have the following effects:
	1% Increase			1% Decrease
(Dollars in millions)
Increase (decrease) from change in health care cost trend rates:
Postretirement benefit expense	$	0		$	0
Postretirement benefit liability		0.2			(0.2	)
Incentive Plan
The Company has short-term management incentive plans that pay cash bonuses if certain Company performance and individual goals are met. The charge to operating expense for these plans was $2.3 million in 2013, $5.2 million in 2012 and $5.6 million in 2011.

Common_Stock_and_Senior_Conver

Common Stock and Senior Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2013
Text Block [Abstract]	'
Common Stock and Senior Convertible Preferred Stock	'
	16. Common Stock and Senior Convertible Preferred Stock
	Changes in senior convertible preferred stock, common stock and treasury stock for the three years ended December 31, 2013 are as follows:
		Year Ended December 31,
		2013			2012			2011
	(Shares in thousands)
	Senior Convertible Preferred Stock:
	Balance at beginning and end of year		0			0			0
	Common Stock:
	Balance at beginning of year		21,585			21,309			21,278
	Issued for employee stock plans		137			276			31
	Balance at end of year		21,722			21,585			21,309
	Treasury Stock:
	Balance at beginning of year		(951	)		(706	)		(700	)
	Shares repurchased		(439	)		(245	)		(6	)
	Balance at end of year		(1,390	)		(951	)		(706	)

Fair_Value_of_Financial_Instru

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair Value of Financial Instruments	'
	17. Fair Value of Financial Instruments
	Carrying amounts and the related estimated fair values of the Company’s financial instruments as of December 31, 2013 and 2012 are as follows:
			December 31, 2013				December 31, 2012
			Fair Value		Carrying		Fair Value		Carrying
					Value				Value
	(Dollars in millions)
	Financial assets:
	Cash and cash equivalents		$	82.2	$	82.2	$	66.7	$	66.7
	Investments and other assets(a)			1.4		1.4		1.4		1.4
	Financial liabilities:
	Long-term debt (including current portion)		$	331.2	$	303.1	$	331.1	$	296.1
	(a)	Excludes equity method investments.
	Cash – The carrying amount approximates fair value because of the short maturity of those instruments.
	Investments and other assets – Represents the broker-quoted cash surrender value on life insurance policies. The cash surrender value asset is classified as Level 2 in the valuation hierarchy and is measured from values received from the insuring entity.
	Long-term 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).

Commitments_and_Contingent_Lia

Commitments and Contingent Liabilities	12 Months Ended
	Dec. 31, 2013
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 three states in which the plaintiffs claim they suffered a variety of illnesses (including cancer) as a result of exposure to coal tar pitch sold by the defendants. There are approximately 111 plaintiffs in 61 cases pending as of December 31, 2013 as compared to 136 plaintiffs in 75 cases pending as of December 31, 2012. As of December 31, 2013, there are a total of 57 cases pending in state court in Pennsylvania, three in Arkansas, and one case pending in state court in Tennessee.
	The plaintiffs in all 61 pending cases seek to recover compensatory damages, while plaintiffs in 56 cases also seek to recover punitive damages. The plaintiffs in the 57 cases filed in Pennsylvania state court seek unspecified damages in excess of the court’s minimum jurisdictional limit. The plaintiffs in the Arkansas state court cases each seek compensatory damages in excess of $50,000 in addition to punitive damages. The plaintiffs in the Tennessee state court case each seek damages of $15.0 million. The other defendants in these lawsuits vary from case to case and include companies such as Beazer East, Inc., United States Steel Corporation, Honeywell International Inc., Vertellus Specialties Inc., Dow Chemical Company, UCAR Carbon Company, Inc., Exxon Mobil Corporation, SGL Carbon Corporation and Alcoa, Inc. Discovery is proceeding in these cases. No trial dates have been set in any of these cases.
	The Company has not provided a reserve for these lawsuits because, at this time, the Company cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. The timing of resolution of these cases cannot be reasonably determined. Although Koppers Inc. is vigorously defending these cases, an unfavorable resolution of these matters may have a material adverse effect on the Company’s business, financial condition, cash flows and results of operations.
	Gainesville. Koppers Inc. operated a utility pole treatment plant in Gainesville from December 29, 1988 until its closure in 2009. The property upon which the utility pole treatment plant was located was sold by Koppers Inc. to Beazer East, Inc. in 2010.
	In November 2010, a class action complaint was filed in the Circuit Court of the Eighth Judicial Circuit located in Alachua County, Florida by residential real property owners located in a neighborhood west of and immediately adjacent to the former utility pole treatment plant in Gainesville. The complaint named Koppers Holdings Inc., Koppers Inc., Beazer East and several other parties as defendants. In a Second Amended Complaint, plaintiffs define the putative class as consisting of all persons who are present record owners of residential real properties located in an area within a two-mile radius of the former Gainesville wood treating plant. Plaintiffs further allege that chemicals and contaminants from the Gainesville plant have contaminated real properties within the two mile geographical area, have caused property damage (diminution in value) and have placed residents and owners of the putative class properties at an elevated risk of exposure to and injury from the chemicals at issue. The Second Amended complaint seeks damages for diminution in property values, the establishment of a medical monitoring fund and punitive damages.
	The case was removed to the United States District Court for the Northern District of Florida in December 2010. On May 31, 2013, the Court entered a scheduling order for class certification, which sets out discovery deadlines leading up to motions for class certification and opposition to those motions. Under the terms of the order, depositions relating to class certification will not commence until the court has disposed of all pending motions to dismiss. The district court dismissed Koppers Holdings Inc. on September 9, 2013 on the ground that there was no personal jurisdiction. Plaintiffs’ appeal of the dismissal of Koppers Holdings Inc. was dismissed on December 2, 2013. However, the court has not yet ruled on all pending motions to dismiss filed by other defendants. Therefore, depositions relating to class certification have not yet commenced.
	The Company has not provided a reserve for this matter because, at this time, it cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. The timing of resolution of this case cannot be reasonably determined. Although the Company is vigorously defending this case, an unfavorable resolution of this matter may have a material adverse effect on the Company’s business, financial condition, cash flows and results of operations.
	Other Matters. In July 2012, Koppers Netherlands B.V.’s (Koppers Netherlands) coal tar distillation plant suffered a series of electrical disruptions which significantly affected plant operations and prevented the resumption of plant operations for a period of approximately three weeks. As a result of the suspension of operations, the coal tar distillation plant was unable to provide steam and other services to an adjacent unaffiliated plant. This unaffiliated plant and Koppers Netherlands’ plant share certain services and plant infrastructure under a cost sharing agreement. In September 2012, Koppers Netherlands received a business interruption claim from the owner of the unaffiliated plant that included an initial claim for lost profits of approximately $1.7 million. In July 2013 the owner of the unaffiliated plant filed a request for arbitration with the Netherlands Arbitration Institute seeking damages for the business interruption claim plus interest, costs and legal fees. In its statement of claim to the arbitration board, the owner of the unaffiliated facility has claimed damages of at least $3.1 million for these costs. The arbitration hearing has tentatively been scheduled for June 2014.
	Koppers Netherlands has not received detailed information used by the unaffiliated plant to determine this alleged loss, and, as a result, Koppers Netherlands is unable to determine the validity of the actual loss incurred. The Company has not provided a reserve for the claimed lost profits because, at this time, it cannot reasonably determine the probability of such loss, and the amount of such loss, if any, cannot be reasonably estimated. The Company does not currently believe that resolution of this matter will involve a loss contingency that would be material to the financial statements.
	Environmental and Other Litigation Matters
	The Company and its subsidiaries are subject to federal, state, local and foreign laws and regulations and potential liabilities relating to the protection of the environment and human health and safety including, among other things, the cleanup of contaminated sites, the treatment, storage and disposal of wastes, the discharge of effluent into waterways, the emission of substances into the air and various health and safety matters. The Company’s subsidiaries expect to incur substantial costs for ongoing compliance with such laws and regulations. The Company’s subsidiaries may also face governmental or third-party claims, or otherwise incur costs, relating to cleanup of, or for injuries resulting from, contamination at sites associated with past and present operations. The Company accrues for environmental liabilities when a determination can be made that a liability is probable and reasonably estimable.
	Environmental and Other Liabilities Retained or Assumed by Others. The Company’s subsidiaries have agreements with former owners of certain of their operating locations under which the former owners retained, assumed and/or agreed to indemnify such subsidiaries against certain environmental and other liabilities. The most significant of these agreements was entered into at Koppers Inc.’s formation on December 29, 1988 (the “Acquisition”). Under the related asset purchase agreement between Koppers Inc. and Beazer East, subject to certain limitations, Beazer East retained the responsibility for and agreed to indemnify Koppers Inc. against certain liabilities, damages, losses and costs, including, with certain limited exceptions, liabilities under and costs to comply with environmental laws to the extent attributable to acts or omissions occurring prior to the Acquisition and liabilities related to products sold by Beazer East prior to the Acquisition (the “Indemnity”). Beazer Limited, the parent company of Beazer East, unconditionally guaranteed Beazer East’s performance of the Indemnity pursuant to a guarantee (the “Guarantee”). In 1998, the parent company of Beazer East purchased an insurance policy under which the funding and risk of certain environmental and other liabilities relating to the former Koppers Company, Inc. operations of Beazer East (which includes locations purchased from Beazer East by Koppers Inc.) are underwritten by Centre Solutions (a member of the Zurich Group) and Swiss Re. Beazer East is a wholly-owned, indirect subsidiary of Heidelberg Cement AG.
	The Indemnity provides different mechanisms, subject to certain limitations, by which Beazer East is obligated to indemnify Koppers Inc. with regard to certain environmental, product and other liabilities and imposes certain conditions on Koppers Inc. before receiving such indemnification, including, in some cases, certain limitations regarding the time period as to which claims for indemnification can be brought. In July 2004, Koppers Inc. and Beazer East agreed to amend the environmental indemnification provisions of the December 29, 1988 asset purchase agreement to extend the indemnification period for pre-closing environmental liabilities through July 2019. As consideration for the amendment, Koppers Inc. paid Beazer East a total of $7.0 million and agreed to share toxic tort litigation defense costs arising from any sites acquired from Beazer East. The July 2004 amendment did not change the provisions of the Indemnity with respect to indemnification for non-environmental claims, such as product liability claims, which claims may continue to be asserted after July 2019.
	Qualified expenditures under the Indemnity are not subject to a monetary limit. Qualified expenditures under the Indemnity include (i) environmental cleanup liabilities required by third parties, such as investigation, remediation and closure costs, relating to pre-December 29, 1988, or (“Pre-Closing”), acts or omissions of Beazer East or its predecessors; (ii) environmental claims by third parties for personal injuries, property damages and natural resources damages relating to Pre-Closing acts or omissions of Beazer East or its predecessors; (iii) punitive damages for the acts or omissions of Beazer East and its predecessors without regard to the date of the alleged conduct and (iv) product liability claims for products sold by Beazer East or its predecessors without regard to the date of the alleged conduct. If the third party claims described in sections (i) and (ii) above are not made by July 2019, Beazer East will not be required to pay the costs arising from such claims under the Indemnity. However, with respect to any such claims which are made by July 2019, Beazer East will continue to be responsible for such claims under the Indemnity beyond July 2019. The Indemnity provides for the resolution of issues between Koppers Inc. and Beazer East by an arbitrator on an expedited basis upon the request of either party. The arbitrator could be asked, among other things, to make a determination regarding the allocation of environmental responsibilities between Koppers Inc. and Beazer East. Arbitration decisions under the Indemnity are final and binding on the parties.
	Contamination has been identified at most manufacturing and other sites of the Company’s subsidiaries. One site currently owned and operated by Koppers Inc. in the United States is listed on the National Priorities List promulgated under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, as amended (“CERCLA”). Currently, at the properties acquired from Beazer East (which include all of the National Priorities List sites and all but one of the sites permitted under the Resource Conservation and Recovery Act (“RCRA”)), a significant portion of all investigative, cleanup and closure activities are being conducted and paid for by Beazer East pursuant to the terms of the Indemnity. In addition, other of Koppers Inc.’s sites are or have been operated under RCRA and various other environmental permits, and remedial and closure activities are being conducted at some of these sites.
	To date, the parties that retained, assumed and/or agreed to indemnify the Company against the liabilities referred to above, including Beazer East, have performed their obligations in all material respects. The Company believes that, for the last three years ended December 31, 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 operates a coal tar pitch terminal near the site. Koppers Inc. has responded to an Environmental Protection Agency (“EPA”) information request and has executed a PRP agreement which outlines the process to develop an allocation of past and future costs among more than 80 parties to the site. Koppers Inc. believes it is a de minimus contributor at the site. Additionally, a separate natural resources damages assessment (“NRDA”) is being conducted by a local trustee group. The NRDA is intended to identify further information necessary to estimate liabilities for remediation based settlements of national resource damages (“NRD”) claims. Koppers Inc. may also incur liabilities under the NRD process and has entered into a separate process to develop an allocation of NRD cost.
	In March 2012, a draft Feasibility Study (“FS”) was submitted to EPA by the Lower Willamette Group, a group of certain PRPs which has been conducting the investigation of the site. The draft FS identifies ten possible remedial alternatives which range in cost from approximately $170 million to $1.8 billion. The FS does not determine who is responsible for remediation costs or select remedies. The FS is under review by the EPA which will issue a final decision on the nature and extent of the final remediation. Responsibility for implementing and funding that work will be decided in the separate allocation process.
	In September 2009, Koppers Inc. received a general notice letter notifying it that it may be a PRP at the Newark Bay CERCLA site. In January 2010, Koppers Inc. submitted a response to the general notice letter asserting that Koppers Inc. is a de minimus party at this site.
	Other than the estimated costs of participating in the PRP group at the Portland Harbor and Newark Bay CERCLA sites totaling $1.0 million at December 31, 2013, the Company has not provided a reserve for these matters because there has not been a determination of the total cost of the investigations, the remediation that will be required, the amount of natural resources damages or how those costs will be allocated among the PRPs. Accordingly, the Company believes that it cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. An unfavorable resolution of these matters may have a material adverse effect on the Company’s business, financial condition, cash flows and results of operations.
	Australian Environmental Matters. Soil and groundwater contamination has been detected at certain of the Company’s Australian facilities. At the Company’s tar distillation facility in Newcastle, New South Wales, Australia, soil contamination from an abandoned underground coal tar pipeline and other groundwater contamination have been detected at a property adjacent to the facility. In 2011, the Company and the owner of the adjacent property reached an agreement in which the Company will contribute $1.6 million and the owner of the adjacent property will contribute $7.5 million toward remediation of the property. The agreement provides that the Company will assume responsibility for the management of the remediation effort and will indemnify the current owner for any remediation costs in excess of its agreed contribution. At the completion of the remediation, the agreement provides that the property will be transferred to the Company. The remediation project commenced in 2011 and the Company has reserved its expected remaining remediation costs of $4.1 million and has recorded a receivable, net of cash collections, from the owner of the adjacent property of $2.7 million as of December 31, 2013.
	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 $5.6 million as of December 31, 2013.
	Environmental Reserves Rollforward. The following table reflects changes in the accrued liability for environmental matters, of which $8.2 million and $8.5 million are classified as current liabilities at December 31, 2013 and 2012, respectively:
		Year Ended December 31,
		2013			2012
	(Dollars in millions)
	Balance at beginning of year		$14.10			$17.70
	Expense		1.8			1
	Reversal of reserves		(1.2	)		(0.4	)
	Cash expenditures		(0.9	)		(4.6	)
	Currency translation		(1.9	)		0.4
	Balance at end of year		$11.90			$14.10
	The reversal of reserves includes a reversal of $1.1 million due to the sale of a property to an unaffiliated third party in September 2013. The unaffiliated third party assumed the site’s remediation liabilities.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2013
Related Party Transactions [Abstract]	'
Related Party Transactions	'
	19. Related Party Transactions
	As of December 31, 2013, the Company has loaned $9.5 million to TKK, a 30-percent owned company in China. The loan is repayable in November 2014.

Subsequent_Event

Subsequent Event	12 Months Ended
	Dec. 31, 2013
Subsequent Events [Abstract]	'
Subsequent Event	'
	20. Subsequent Event
	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 expects to ramp down production at the Uithoorn facility over the first six months of 2014 as it transitions production to other Company-owned European facilities. The Company expects to discontinue distillation activities by mid-2014.
	The Company recorded a fixed and intangible asset impairment charge of $7.0 million in the fourth quarter of 2013 and it expects to record additional charges of approximately $25 million in 2014 related to severance, accelerated depreciation, disentanglement costs, demolition, and site remediation.

Selected_Quarterly_Financial_D

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Selected Quarterly Financial Data (Unaudited)	'
	21. Selected Quarterly Financial Data (Unaudited)
	The following is a summary of the quarterly results of operations for the years ended December 31, 2013 and 2012:
			Year Ended December 31, 2013
			1st Quarter		2nd Quarter			3rd Quarter		4th Quarter			Fiscal Year
	(Dollars in millions, except per share amounts)
	Statement of operations data:
	Net sales		$	370.4	$	370.9		$	395.2	$	341.8		$	1,478.30
	Operating profit(a)			24.9		28.5			39.1		7.8			100.3
	Income from continuing operations			11.4		14.8			19.6		(5.6	)		40.2
	Net income (loss)			11.5		14.7			19.5		(5.6	)		40.1
	Net income (loss) attributable to Koppers			11		14.4			19.1		(4.1	)		40.4
	Common stock data:
	Earnings (loss) per common share attributable to Koppers common shareholders:(b)
	Basic –
	Continuing operations		$	0.53	$	0.7		$	0.93	$	(0.20	)	$	1.96
	Discontinued operations(c)			0		(0.01	)		0		0			0
	Earnings per basic common share		$	0.53	$	0.69		$	0.93	$	(0.20	)	$	1.96
	Diluted –
	Continuing operations		$	0.53	$	0.7		$	0.92	$	(0.20	)	$	1.94
	Discontinued operations(c)			0		(0.01	)		0		0			0
	Earnings per diluted common share		$	0.53	$	0.69		$	0.92	$	(0.20	)	$	1.94
	Dividends declared per common share		$	0.25	$	0.25		$	0.25	$	0.25		$	1
	Price range of common stock:
	High		$	45.72	$	46.48		$	42.09	$	49.99		$	49.99
	Low			38.7		37.45			34.69		41.61			34.69
			Year Ended December 31, 2012
			1st Quarter		2nd Quarter			3rd Quarter		4th Quarter			Fiscal Year
	(Dollars in millions, except per share amounts)
	Statement of operations data:
	Net sales		$	380.9	$	411.3		$	387.9	$	374.9		$	1,555.00
	Operating profit			29.2		40.7			30.8		25.9			126.6
	Income from continuing operations			15.8		21.1			16.2		14.2			67.3
	Net income			15.9		20.9			16.2		14.2			67.2
	Net income attributable to Koppers			15.6		20.4			16		13.6			65.6
	Common stock data:
	Earnings (loss) per common share attributable to Koppers common shareholders:(b)
	Basic –
	Continuing operations		$	0.74	$	1		$	0.77	$	0.66		$	3.18
	Discontinued operations(c)			0.01		(0.01	)		0		0			(0.01	)
	Earnings per basic common share		$	0.75	$	0.99		$	0.77	$	0.66		$	3.17
	Diluted –
	Continuing operations		$	0.74	$	0.99		$	0.77	$	0.65		$	3.14
	Discontinued operations(c)			0.01		(0.01	)		0		0			(0.01	)
	Earnings per diluted common share		$	0.75	$	0.98		$	0.77	$	0.65		$	3.13
	Dividends declared per common share		$	0.24	$	0.24		$	0.24	$	0.24		$	0.96
	Price range of common stock:
	High		$	40.61	$	40.37		$	37.82	$	38.83		$	40.61
	Low			32.15		31.17			29.3		30.99			29.3
	(a)	In the fourth quarter of 2013, the Company recorded asset impairment charges totaling $11.9 million primarily consisting of writedowns related to the Company’s coal tar distillation facilities located in Uithoorn, the Netherlands; Tangshan, China; and Follansbee, West Virginia.
	(b)	The cumulative sum of quarterly basic and diluted net income per share amounts may not equal total basic and diluted net income per share amounts for the year due to differences in weighted average and equivalent shares outstanding for each of the periods presented.
	(c)	In the fourth quarter of 2011, the Company ceased manufacturing operations at its carbon black facility located in Kurnell, Australia. The results of operations of the carbon black facility have been reclassified to discontinued operations for all periods presented as run-off activities were completed in the first quarter of 2012.

Subsidiary_Guarantor_Informati

Subsidiary Guarantor Information for Koppers Inc. Senior Notes	12 Months Ended
	Dec. 31, 2013
Text Block [Abstract]	'
Subsidiary Guarantor Information for Koppers Inc. Senior Notes	'
	22. Subsidiary Guarantor Information for Koppers Inc. Senior Notes
	On December 1, 2009, Koppers Inc. issued $300.0 million principal value of Senior Notes. Koppers Holdings and each of Koppers Inc.’s 100 percent-owned material domestic subsidiaries other than Koppers Assurance, Inc. fully and unconditionally guarantee the payment of principal and interest on the Senior Notes. The domestic guarantor subsidiaries include Koppers World-Wide Ventures Corporation, Koppers Delaware, Inc., Koppers Concrete Products, Inc., Concrete Partners, Inc., and Koppers Asia LLC. Non-guarantor subsidiaries are owned directly by Koppers Inc. or are owned directly or indirectly by Koppers World-Wide Ventures Corporation.
	The guarantee of a guarantor subsidiary will be automatically and unconditionally released and discharged in the event of:
		¡		any sale of the capital stock or substantially all of the assets of the guarantor subsidiary;
		¡		the designation of the guarantor subsidiary as an unrestricted subsidiary in accordance with the indenture governing the Senior Notes; and
		¡		the legal defeasance, covenant defeasance or satisfaction and discharge of the indenture governing the Senior Notes.
	Koppers Holdings depends on the dividends from the earnings of Koppers Inc. and its subsidiaries to generate the funds necessary to meet its financial obligations, including the payment of any declared dividend of Koppers Holdings. Koppers Inc.’s credit agreement prohibits it from making dividend payments to Koppers Holdings Inc. unless (1) such dividend payments are permitted by the indenture governing Koppers Inc.’s Senior Notes and (2) no event of default or potential default has occurred or is continuing under the credit agreement. The indenture governing Koppers Inc.’s Senior Notes restricts its ability to finance Koppers Holdings Inc.’s payment of dividends if (1) a default has occurred or would result from such financing, (2) a restricted subsidiary of Koppers Inc. which is not a guarantor under the indenture is not able to incur additional indebtedness (as defined in the indenture), and (3) the sum of all restricted payments (as defined in the indenture) have exceeded the permitted amount (referred to as the “basket”) at such point in time.
	The Koppers Inc. revolving credit facility agreement provides for a revolving credit facility of up to $350.0 million at variable interest rates. Borrowings under the revolving credit facility are secured by a first priority lien on substantially all of the assets of Koppers Inc. and its material domestic subsidiaries. The revolving credit facility contains certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends and investments or acquisitions. In addition, such covenants give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios.
	The amount of restricted net assets unavailable for distribution to Koppers Holdings Inc. by Koppers Inc. totals $147 million as of December 31, 2013. Cash dividends paid to Koppers Holdings Inc. by its subsidiaries totaled $38.5 million, $27.6 million and $2.5 million for the years ended December 31, 2013, 2012 and 2011, respectively.
	Separate condensed consolidating financial statement information for Koppers Holdings Inc. (the parent), Koppers Inc., domestic guarantor subsidiaries and non-guarantor subsidiaries as of December 31, 2013 and 2012 and for the years ended December 31, 2013, 2012 and 2011 is as follows. The condensed consolidating statements of comprehensive income for the years ended December 31, 2012 and 2011 and the condensed consolidating balance sheet at December 31, 2012 have been restated to revise the presentation of net income and related investments in subsidiaries under the equity method of accounting, the allocation of deferred tax assets, and the presentation of intercompany lending arrangements. This restatement changed the previously reported amounts for equity income, other income, interest expense, net income attributable to Koppers, comprehensive income attributable to Koppers, receivables, equity investments, deferred tax assets, debt, total assets, Koppers shareholders’ equity, total liabilities and equity 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 statements of cash flows for the years ended December 31, 2012 and 2011 have 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 except for rounding differences. There was no impact on the net increase or decrease in cash for any column.
	Certain amounts for receivables, accounts payable, other noncurrent assets and long-term debt have been reclassified in the Condensed Consolidating Balance Sheet as of December 31, 2012 to reflect affiliated receivables, payables, loans and debt.
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2013
			Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
									Guarantor			Subsidiaries			Adjustments
									Subsidiaries
	(Dollars in millions)
	Net sales		$	0		$	843.7		$	61.8		$	622.2		$	(49.4	)	$	1,478.30
	Cost of sales including depreciation and amortization			0			745.4			43.5			566.9			(49.5	)		1,306.30
	Selling, general and administrative			1.9			41.5			0.7			27.6			0			71.7
	Operating profit (loss)			(1.9	)		56.8			17.6			27.7			0.1			100.3
	Other income (expense)			0			1.3			4.2			2.1			(4.1	)		3.5
	Equity income of subsidiaries			41.7			17.5			11.4			0			(70.6	)		0
	Interest expense			0			26.7			0			4.2			(4.1	)		26.8
	Income taxes			(0.6	)		7.3			16.4			13.7			0			36.8
	Income from continuing operations			40.4			41.6			16.8			11.9			(70.5	)		40.2
	Discontinued operations			0			0.1			0			(0.2	)		0			(0.1	)
	Noncontrolling interests			0			0			0			(0.3	)		0			(0.3	)
	Net income attributable to Koppers		$	40.4		$	41.7		$	16.8		$	12		$	(70.5	)	$	40.4
	Comprehensive income attributable to Koppers		$	52.3		$	53.5		$	8.4		$	13.8		$	(75.7	)	$	52.3
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2012
			Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
									Guarantor			Subsidiaries			Adjustments
									Subsidiaries
	(Dollars in millions)
	Net sales		$	0		$	893.2		$	97.5		$	638.4		$	(74.1	)	$	1,555.00
	Cost of sales including depreciation and amortization			0			786.6			78			562			(73.8	)		1,352.80
	Selling, general and administrative			1.6			45.1			2.1			26.8			0			75.6
	Operating profit (loss)			(1.6	)		61.5			17.4			49.6			(0.3	)		126.6
	Other income (expense)			0			0.4			6.1			0.6			(5.2	)		1.9
	Equity income of subsidiaries			66.6			40.8			28.8			0.1			(136.3	)		0
	Interest expense			0			27.4			0			5.8			(5.3	)		27.9
	Income taxes			(0.6	)		8.7			12.5			12.7			0			33.3
	Income from continuing operations			65.6			66.6			39.8			31.8			(136.5	)		67.3
	Discontinued operations			0			0			0			(0.1	)		0			(0.1	)
	Noncontrolling interests			0			0			0			1.6			0			1.6
	Net income attributable to Koppers		$	65.6		$	66.6		$	39.8		$	30.1		$	(136.5	)	$	65.6
	Comprehensive income attributable to Koppers		$	73.7		$	74.8		$	44		$	32.4		$	(151.2	)	$	73.7
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2011
			Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
									Guarantor			Subsidiaries			Adjustments
									Subsidiaries
	(Dollars in millions)
	Net sales		$	0		$	854.1		$	72.6		$	585.2		$	(45.7	)	$	1,466.20
	Cost of sales including depreciation and amortization			0			762.9			55			497			(45.7	)		1,269.20
	Selling, general and administrative			1.2			41.6			1.8			29.7			0			74.3
	Operating profit (loss)			(1.2	)		49.6			15.8			58.5			0			122.7
	Other income (expense)			0			0.3			5.5			0.4			(5.5	)		0.7
	Equity income of subsidiaries			37.7			22.9			1.3			0			(61.9	)		0
	Interest expense			0			27.4			0.1			5.2			(5.5	)		27.2
Income taxes			(0.4	)		7.7			0.8			30.6			0			38.7
Income from continuing operations			36.9			37.7			21.7			23.1			(61.9	)		57.5
Discontinued operations			0			0			0			(19.9	)		0			(19.9	)
Noncontrolling interests			0			0			0			0.7			0			0.7
Net income attributable to Koppers		$	36.9		$	37.7		$	21.7		$	2.5		$	(61.9	)	$	36.9
Comprehensive income attributable to Koppers		$	18.9		$	19.7		$	17.3		$	(1.4	)	$	(35.6	)	$	18.9
Condensed Consolidating Balance Sheet
December 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents		$	0		$	29.9		$	0.1		$	52.2		$	0		$	82.2
Receivables, net			0			75.6			9.3			82			0			166.9
Affiliated receivables			0.2			1.1			3.9			2.3			(7.5	)		0
Inventories, net			0			86.1			0			82.9			(0.2	)		168.8
Deferred tax assets			0			7.9			1.5			0.6			0			10
Other current assets			0			7.3			0.6			37.3			0			45.2
Total current assets			0.2			207.9			15.4			257.3			(7.7	)		473.1
Equity investments			174.7			333.5			182.9			4.6			(689.1	)		6.6
Property, plant and equipment, net			0			112.2			0			84.8			0			197
Goodwill			0			39.8			0			32.9			0			72.7
Deferred tax assets			0			2.4			(1.4	)		8.3			0			9.3
Affiliated loan receivables			0			8.5			123.8			40.9			(173.2	)		0
Other noncurrent assets			0			15			0			11.2			0			26.2
Total assets		$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
LIABILITIES AND EQUITY
Accounts payable		$	0		$	48.3		$	6.7		$	52.6		$	0		$	107.6
Affiliated payables			0			1.9			4			8.6			(14.5	)		0
Accrued liabilities			5.1			27.8			0.5			54.1			0			87.5
Total current liabilities			5.1			78			11.2			115.3			(14.5	)		195.1
Long-term debt			0			296.5			0			6.6			0			303.1
Affiliated debt			0			109.5			8.5			55.2			(173.2	)		0
Other long-term liabilities			0			67.6			2.5			26.8			0			96.9
Total liabilities			5.1			551.6			22.2			203.9			(187.7	)		595.1
Koppers shareholders’ equity			169.8			167.7			298.5			216.1			(682.3	)		169.8
Noncontrolling interests			0			0			0			20			0			20
Total liabilities and equity		$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
Condensed Consolidating Balance Sheet
December 31, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents		$	0		$	4.8		$	0		$	61.9		$	0		$	66.7
Receivables, net			0			80.2			6.3			77.8			0			164.3
Affiliated receivables			0.7			0			119			9			(128.7	)		0
Inventories, net			0			102.2			0			93.9			(0.3	)		195.8
Deferred tax assets			0			9.4			5.5			0.2			0			15.1
Other current assets			0			6.4			2.8			30.1			0			39.3
Total current assets			0.7			203			133.6			272.9			(129.0	)		481.2
Equity investments			154.9			648.3			183.8			3.8			(985.0	)		5.8
Property, plant and equipment, net			0			105.7			0			55.4			0			161.1
Goodwill			0			39.8			0			35.8			0			75.6
Deferred tax assets			0			14.9			2.1			10.2			0			27.2
Affiliated loan receivables			0			7.7			326.3			39.3			(373.3	)		0
Other noncurrent assets			0			15.7			0			13.4			0			29.1
Total assets		$	155.6		$	1,035.10		$	645.8		$	430.8		$	(1,487.3	)	$	780
LIABILITIES AND EQUITY
Accounts payable		$	0.1		$	51.4		$	1.7		$	50.3		$	0		$	103.5
Affiliated payables			0			120.8			7.6			6.4			(134.8	)		0
Accrued liabilities			4.9			15.9			12.2			44.7			0			77.7
Total current liabilities			5			188.1			21.5			101.4			(134.8	)		181.2
Long-term debt			0			296.1			0			0			0			296.1
Affiliated debt			0			301			7.7			64.6			(373.3	)		0
Other long-term liabilities			0			101.2			2.4			31			0			134.6
Total liabilities			5			886.4			31.6			197			(508.1	)		611.9
Koppers shareholders’ equity			150.6			148.7			614.2			216.3			(979.2	)		150.6
Noncontrolling interests			0			0			0			17.5			0			17.5
Total liabilities and equity		$	155.6		$	1,035.10		$	645.8		$	430.8		$	(1,487.3	)	$	780
Condensed Consolidating Statement of Cash Flows
For the Year Ended December 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities		$	37.8		$	278.7		$	130.1		$	47.6		$	(376.6	)	$	117.6
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions			0			(23.3	)		0			(51.9	)		0			(75.2	)
(Loans to) repayments from affiliates			0			(0.8	)		193.2			(1.7	)		(190.7	)		0
Net cash proceeds (payments) from divestitures and asset sales			0			1.3			0			1.6			0			2.9
Net cash used in investing activities			0			(22.8	)		193.2			(52.0	)		(190.7	)		(72.3	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt			0			0			0			6.6			0			6.6
Borrowings of affiliated long-term debt			0			(191.5	)		0.8			0			190.7			0
Deferred financing costs			0			(1.3	)		0			0			0			(1.3	)
Dividends paid			(20.5	)		(38.5	)		(324.0	)		(14.7	)		376.6			(21.1	)
Stock issued and repurchased			(17.3	)		0			0			0			0			(17.3	)
Other financing receipts			0			0.5			0			2.3			0			2.8
Net cash provided by (used in) financing activities			(37.8	)		(230.8	)		(323.2	)		(5.8	)		567.3			(30.3	)
Effect of exchange rates on cash			0			0			0			0.5			0			0.5
Net increase in cash and cash equivalents			0			25.1			0.1			(9.7	)		0			15.5
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		$	29.9		$	0.1		$	52.2		$	0		$	82.2
Condensed Consolidating Statement of Cash Flows
For the Year Ended December 31, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities		$	26.1		$	44.6		$	8.7		$	30.9		$	(32.5	)	$	77.8
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions			0			(21.3	)		0			(21.6	)		0			(42.9	)
Loan repayment by related party			0			0			0			2.2			0			2.2
(Loans to) repayments from affiliates			0			0.3			(8.4	)		(2.7	)		10.8			0
Net cash proceeds (payments) from divestitures and asset sales			0			0.4			0			0.4			0			0.8
Net cash used in investing activities			0			(20.6	)		(8.4	)		(21.7	)		10.8			(39.9	)
Cash provided by (used in) financing activities:
Repayments of long-term debt			0			(6.4	)		0			0			0			(6.4	)
Borrowings of affiliated long-term debt			0			13.3			(0.3	)		(2.2	)		(10.8	)		0
Deferred financing costs			0			(0.1	)		0			0			0			(0.1	)
Dividends paid			(19.5	)		(27.6	)		0			(4.9	)		32.5			(19.5	)
Stock issued and repurchased			(6.6	)		0			0			0			0			(6.6	)
Other financing receipts			0			1.6			0			3.7			0			5.3
Net cash provided by (used in) financing activities			(26.1	)		(19.2	)		(0.3	)		(3.4	)		21.7			(27.3	)
Effect of exchange rates on cash			0			0			0			2			0			2
Net increase in cash and cash equivalents			0			4.8			0			7.8			0			12.6
Cash and cash equivalents at beginning of year			0			0			0			54.1			0			54.1
Cash and cash equivalents at end of period		$	0		$	4.8		$	0		$	61.9		$	0		$	66.7
Condensed Consolidating Statement of Cash Flows
For the Year Ended December 31, 2011
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities			$18.20		$	30		$	(15.5	)	$	54.8		$	(10.6	)	$	76.9
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions			0			(24.5	)		0			(9.3	)		0			(33.8	)
Loan to related party			0			0			0			(11.7	)		0			(11.7	)
(Loans to) repayments from affiliates			0			1.2			16.7			(0.3	)		(17.6	)		0
Net cash proceeds from divestitures and asset sales			0			0.7			0			0.1			0			0.8
Net cash used in investing activities			0			(22.6	)		16.7			(21.2	)		(17.6	)		(44.7	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt			0			6.3			0			(0.9	)		0			5.4
Borrowings of affiliated long-term debt			0			(19.2	)		(1.2	)		2.8			17.6			0
Deferred financing costs			0			(0.5	)		0			0			0			(0.5	)
Dividends paid			(18.2	)		(2.5	)		0			(8.1	)		10.6			(18.2	)
Net cash provided by (used in) financing activities			(18.2	)		(15.9	)		(1.2	)		(6.2	)		28.2			(13.3	)
Effect of exchange rates on cash			0			0.1			0			(0.2	)		0			(0.1	)
Net increase (decrease) in cash and cash equivalents			0			(8.4	)		0			27.2			0			18.8
Cash and cash equivalents at beginning of year			0			8.4			0			26.9			0			35.3
Cash and cash equivalents at end of period		$	0		$	0		$	0		$	54.1		$	0		$	54.1

Subsidiary_Guarantor_Informati1

Subsidiary Guarantor Information for Shelf Registration	12 Months Ended
	Dec. 31, 2013
Text Block [Abstract]	'
Subsidiary Guarantor Information for Shelf Registration	'
	23. Subsidiary Guarantor Information for Shelf Registration
	Under a registration statement on Form S-3, Koppers Holdings may sell a combination of securities, including common stock, debt securities, preferred stock, depository shares, warrants and units, from time to time in one or more offerings. In addition, Koppers Inc. may sell debt securities from time to time under the registration statement. Debt securities may be fully and unconditionally guaranteed, on a joint and several basis, by Koppers Holdings, Koppers Inc. and/or other guarantor subsidiaries which will correspond to certain subsidiaries in the United States, Europe and Australia which are 100 percent owned by either Koppers Holdings or Koppers Inc. The non-guarantor subsidiaries consist of certain subsidiaries in the United States, China, India and Mauritius. Non-guarantor subsidiaries are owned directly by Koppers Inc. or are owned directly or indirectly by foreign guarantor subsidiaries. The guarantor subsidiaries that issue guarantees, if any, will be determined when a debt offering actually occurs under the registration statement and accordingly, the condensed consolidating financial information for subsidiary guarantors will be revised to identify the subsidiaries that actually provided guarantees. These guarantees will be governed pursuant to a supplement indenture which the trustee and the issuing company would enter into concurrent with the debt offering.
	Koppers Holdings depends on the dividends from the earnings of Koppers Inc. and its subsidiaries to generate the funds necessary to meet its financial obligations, including the payment of any declared dividend of Koppers Holdings. Koppers Inc.’s credit agreement prohibits it from making dividend payments to Koppers Holdings Inc. unless (1) such dividend payments are permitted by the indenture governing Koppers Inc.’s Senior Notes and (2) no event of default or potential default has occurred or is continuing under the credit agreement. The indenture governing Koppers Inc.’s Senior Notes restricts its ability to finance Koppers Holdings Inc.’s payment of dividends if (1) a default has occurred or would result from such financing, (2) a restricted subsidiary of Koppers Inc. which is not a guarantor under the indenture is not able to incur additional indebtedness (as defined in the indenture), and (3) the sum of all restricted payments (as defined in the indenture) have exceeded the permitted amount (referred to as the “basket”) at such point in time.
	The Koppers Inc. revolving credit facility agreement provides for a revolving credit facility of up to $350.0 million at variable interest rates. Borrowings under the revolving credit facility are secured by a first priority lien on substantially all of the assets of Koppers Inc. and its material domestic subsidiaries. The revolving credit facility contains certain covenants for Koppers Inc. and its restricted subsidiaries that limit capital expenditures, additional indebtedness, liens, dividends and investments or acquisitions. In addition, such covenants give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios.
	The amount of restricted net assets unavailable for distribution to Koppers Holdings Inc. by its subsidiaries totals $147 million as of December 31, 2013. Cash dividends paid to Koppers Holdings Inc. by its subsidiaries totaled $38.5 million, $27.6 million and $2.5 million for the years ended December 31, 2013, 2012 and 2011, respectively.
	Separate condensed consolidating financial statement information for the parent, Koppers Inc., domestic guarantor subsidiaries, foreign guarantor subsidiaries and non-guarantor subsidiaries as of December 31, 2013 and 2012 and for the years ended December 31, 2013, 2012 and 2011 is as follows. The condensed consolidating statements of comprehensive income for the years ended December 31, 2012 and 2011 and the condensed consolidating balance sheet at December 31, 2012 have been restated to revise the presentation of net income and related investments in subsidiaries under the equity method of accounting, the allocation of deferred tax assets, and the presentation of intercompany lending arrangements. This restatement changed the previously reported amounts for equity income, other income, interest expense, net income attributable to Koppers, comprehensive income attributable to Koppers, receivables, equity investments, deferred tax assets, debt, total assets, Koppers shareholders’ equity, total liabilities and equity 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 statements of cash flows for the years ended December 31, 2012 and 2011 have 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 except for rounding differences. There was no impact on the net increase or decrease in cash for any column.
	Certain amounts for receivables, accounts payable, other noncurrent assets and long-term debt have been reclassified in the Condensed Consolidating Balance Sheet as of December 31, 2012 to reflect affiliated receivables, payables loans and debt.
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	843.7		$	61.8		$	462.7		$	162.1		$	(52.0	)	$	1,478.30
	Cost of sales including depreciation and amortization		0			745.4			43.5			413.3			156.2			(52.1	)		1,306.30
	Selling, general and administrative		1.9			41.5			0.7			22.1			5.5			0			71.7
	Operating profit (loss)		(1.9	)		56.8			17.6			27.3			0.4			0.1			100.3
	Other income (expense)		0			1.3			4.2			0.9			1.2			(4.1	)		3.5
	Equity income (loss) of subsidiaries		41.7			17.5			11.4			(1.3	)		0			(69.3	)		0
	Interest expense		0			26.7			0			3.2			1			(4.1	)		26.8
	Income taxes		(0.6	)		7.3			16.4			12.2			1.5			0			36.8
	Income from continuing operations		40.4			41.6			16.8			11.5			(0.9	)		(69.2	)		40.2
	Discontinued operations		0			0.1			0			(0.2	)		0			0			(0.1	)
	Noncontrolling interests		0			0			0			0			(0.3	)		0			(0.3	)
	Net income attributable to Koppers	$	40.4		$	41.7		$	16.8		$	11.3		$	(0.6	)	$	(69.2	)	$	40.4
	Comprehensive income attributable to Koppers	$	52.3		$	53.5		$	8.4		$	10.1		$	0.4		$	(72.4	)	$	52.3
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2012
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	893.2		$	97.5		$	480		$	158.6		$	(74.3	)	$	1,555.00
	Cost of sales including depreciation and amortization		0			786.6			78			414.6			147.6			(74.0	)		1,352.80
	Selling, general and administrative		1.6			45.1			2.1			23.4			3.4			0			75.6
	Operating profit (loss)		(1.6	)		61.5			17.4			42			7.6			(0.3	)		126.6
	Other income (expense)		0			0.4			6.1			0.2			0.4			(5.2	)		1.9
	Equity income of subsidiaries		66.6			40.8			28.8			1.4			0			(137.6	)		0
	Interest expense		0			27.4			0			4.2			1.5			(5.2	)		27.9
	Income taxes		(0.6	)		8.7			12.5			10.5			2.2			0			33.3
	Income from continuing operations		65.6			66.6			39.8			28.9			4.3			(137.9	)		67.3
	Discontinued operations		0			0			0			(0.1	)		0			0			(0.1	)
	Noncontrolling interests		0			0			0			0			1.6			0			1.6
	Net income attributable to Koppers	$	65.6		$	66.6		$	39.8		$	28.8		$	2.7		$	(137.9	)	$	65.6
	Comprehensive income attributable to Koppers	$	73.7		$	74.8		$	44		$	31.5		$	2.8		$	(153.1	)	$	73.7
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2011
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	854.1		$	72.6		$	443.6		$	147		$	(51.1	)	$	1,466.20
	Cost of sales including depreciation and amortization		0			762.9			55			364.2			138.2			(51.1	)		1,269.20
	Selling, general and administrative		1.2			41.6			1.8			26.2			3.5			0			74.3
	Operating profit (loss)		(1.2	)		49.6			15.8			53.2			5.3			0			122.7
	Other income (expense)		0			0.3			5.5			0.1			0.3			(5.5	)		0.7
	Equity income of subsidiaries		37.7			22.9			1.3			1.4			0			(63.3	)		0
	Interest expense		0			27.4			0.1			4.8			0.5			(5.6	)		27.2
	Income taxes		(0.4	)		7.7			0.8			28.7			1.9			0			38.7
	Income from continuing operations		36.9			37.7			21.7			21.2			3.2			(63.2	)		57.5
	Discontinued operations		0			0			0			(19.9	)		0			0			(19.9	)
	Noncontrolling interests		0			0			0			0			0.7			0			0.7
Net income attributable to Koppers	$	36.9		$	37.7		$	21.7		$	1.3		$	2.5		$	(63.2	)	$	36.9
Comprehensive income attributable to Koppers	$	18.9		$	19.7		$	17.3		$	(3.7	)	$	3.5		$	(36.8	)	$	18.9
Condensed Consolidating Balance Sheet
December 31, 2013
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0		$	29.9		$	0.1		$	43.5		$	8.7		$	0		$	82.2
Receivables, net		0			75.6			9.3			55.5			26.5			0			166.9
Affiliated receivables		0.2			1.1			3.9			0.8			1.6			(7.6	)		0
Inventories, net		0			86.1			0			75.2			7.7			(0.2	)		168.8
Deferred tax assets		0			7.9			1.5			0			0.6			0			10
Other current assets		0			7.3			0.6			17.5			19.8			0			45.2
Total current assets		0.2			207.9			15.4			192.5			64.9			(7.8	)		473.1
Equity investments		174.7			333.5			182.9			50.5			4.5			(739.5	)		6.6
Property, plant and equipment, net		0			112.2			0			38.1			46.7			0			197
Goodwill		0			39.8			0			31.5			1.4			0			72.7
Deferred tax assets		0			2.4			(1.4	)		5.5			2.8			0			9.3
Affiliated loan receivables		0			8.5			123.8			0.1			40.8			(173.2	)		0
Other noncurrent assets		0			15			0			9.9			1.3			0			26.2
Total assets	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
LIABILITIES AND EQUITY
Accounts payable	$	0		$	48.3		$	6.7		$	40.6		$	12		$	0		$	107.6
Affiliated payables		0			1.9			4			0.4			8.4			(14.7	)		0
Accrued liabilities		5.1			27.8			0.5			31.4			22.7			0			87.5
Total current liabilities		5.1			78			11.2			72.4			43.1			(14.7	)		195.1
Long-term debt		0			296.5			0			0			6.6			0			303.1
Affiliated debt		0			109.5			8.5			55.2			0			(173.2	)		0
Other long-term liabilities		0			67.6			2.5			19.6			7.2			0			96.9
Total liabilities		5.1			551.6			22.2			147.2			56.9			(187.9	)		595.1
Koppers shareholders’ equity		169.8			167.7			298.5			180.9			85.5			(732.6	)		169.8
Noncontrolling interests		0			0			0			0			20			0			20
Total liabilities and equity	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
Condensed Consolidating Balance Sheet
December 31, 2012
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
ASSETS
Cash and cash equivalents	$	0		$	4.8		$	0		$	40.7		$	21.2		$	0		$	66.7
Receivables, net		0			80.2			6.3			63.5			14.3			0			164.3
Affiliated receivables		0.7			0			119			2.3			6.9			(128.9	)		0
Inventories, net		0			102.2			0			86.7			7.2			(0.3	)		195.8
Deferred tax assets		0			9.4			5.5			0			0.2			0			15.1
Other current assets		0			6.4			2.8			17.6			12.5			0			39.3
Total current assets		0.7			203			133.6			210.8			62.3			(129.2	)		481.2
Equity investments		154.9			648.3			183.8			43			4			(1,028.2	)		5.8
Property, plant and equipment, net		0			105.7			0			40.7			14.7			0			161.1
Goodwill		0			39.8			0			34.4			1.4			0			75.6
Deferred tax assets		0			14.9			2.1			7.6			2.6			0			27.2
Affiliated loan receivables		0			7.7			326.3			0.1			39.2			(373.3	)		0
Other noncurrent assets		0			15.7			0			12.1			1.3			0			29.1
Total assets	$	155.6		$	1,035.10		$	645.8		$	348.7		$	125.5		$	(1,530.7	)	$	780
LIABILITIES AND EQUITY
Accounts payable	$	0.1		$	51.4		$	1.7		$	40.6		$	9.7		$	0		$	103.5
Affiliated payables		0			120.8			7.6			1.4			8.9			(138.7	)		0
Accrued liabilities		4.9			15.9			12.2			35.8			8.9			0			77.7
Total current liabilities		5			188.1			21.5			77.8			27.5			(138.7	)		181.2
Long-term debt		0			296.1			0			0			0			0			296.1
Affiliated debt		0			301			7.7			64.5			0			(373.2	)		0
Other long-term liabilities		0			101.2			2.4			24.5			6.5			0			134.6
Total liabilities		5			886.4			31.6			166.8			34			(511.9	)		611.9
Koppers shareholders’ equity		150.6			148.7			614.2			181.9			74			(1,018.8	)		150.6
Noncontrolling interests		0			0			0			0			17.5			0			17.5
Total liabilities and equity	$	155.6		$	1,035.10		$	645.8		$	348.7		$	125.5		$	(1,530.7	)	$	780
Condensed Consolidating Statement of Cash Flows
For the Year Ended December 31, 2013
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities	$	37.8		$	278.7		$	130.1		$	39.9		$	7.7		$	(376.6	)	$	117.6
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(23.3	)		0			(22.1	)		(37.5	)		7.7			(75.2	)
(Loans to) repayments from affiliates		0			(0.8	)		193.2			0			(1.7	)		(190.7	)		0
Net cash proceeds from divestitures and asset sales		0			1.3			0			1.1			0.5			0			2.9
Net cash provided by (used in) investing activities		0			(22.8	)		193.2			(21.0	)		(38.7	)		(183.0	)		(72.3	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0			0			0			0			6.6			0			6.6
Borrowings of affiliated long-term debt		0			(191.5	)		0.8			0			0			190.7			0
Deferred financing costs		0			(1.3	)		0			0			0			0			(1.3	)
Dividends paid		(20.5	)		(38.5	)		(324.0	)		(14.1	)		(0.6	)		376.6			(21.1	)
Stock issued and repurchased		(17.3	)		0			0			0			7.7			(7.7	)		(17.3	)
Other financing receipts		0			0.5			0			0			2.3			0			2.8
Net cash provided by (used in) financing activities		(37.8	)		(230.8	)		(323.2	)		(14.1	)		16			559.6			(30.3	)
Effect of exchange rates on cash		0			0			0			(2.0	)		2.5			0			0.5
Net increase (decrease) in cash and cash equivalents		0			25.1			0.1			2.8			(12.5	)		0			15.5
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		$	29.9		$	0.1		$	43.5		$	8.7		$	0		$	82.2
Condensed Consolidating Statement of Cash Flows
For the Year Ended December 31, 2012
	Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
							Guarantor			Guarantor			Subsidiaries			Adjustments
							Subsidiaries			Subsidiaries
(Dollars in millions)
Cash provided by (used in) operating activities	$	26.1		$	44.6		$	8.7		$	29.5		$	1.4		$	(32.5	)	$	77.8
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(21.3	)		0			(31.5	)		(0.5	)		10.4			(42.9	)
Loan repayment by related party		0			0			0			0			2.2			0			2.2
(Loans to) repayments from affiliates		0			0.3			(8.4	)		0			(2.7	)		10.8			0
Net cash proceeds from divestitures and asset sales		0			0.4			0			0.4			0			0			0.8
Net cash provided by (used in) investing activities		0			(20.6	)		(8.4	)		(31.1	)		(1.0	)		21.2			(39.9	)
Cash provided by (used in) financing activities:
Repayments of long-term debt		0			(6.4	)		0			0			0			0			(6.4	)
Borrowings of affiliated long-term debt		0			13.3			(0.3	)		0			(2.2	)		(10.8	)		0
Deferred financing costs		0			(0.1	)		0			0			0			0			(0.1	)
Dividends paid		(19.5	)		(27.6	)		0			(4.9	)		0			32.5			(19.5	)
Stock issued and repurchased		(6.6	)		0			0			0			10.4			(10.4	)		(6.6	)
Other financing receipts		0			1.6			0			0			3.7			0			5.3
Net cash provided by (used in) financing activities		(26.1	)		(19.2	)		(0.3	)		(4.9	)		11.9			11.3			(27.3	)
Effect of exchange rates on cash		0			0			0			2.1			(0.1	)		0			2
Net increase (decrease) in cash and cash equivalents		0			4.8			0			(4.4	)		12.2			0			12.6
Cash and cash equivalents at beginning of year		0			0			0			45.1			9			0			54.1
Cash and cash equivalents at end of period	$	0		$	4.8		$	0		$	40.7		$	21.2		$	0		$	66.7
Condensed Consolidating Statement of Cash Flows
For the Year Ended December 31, 2011
	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	$	18.2		$	30		$	(15.5	)	$	49.5		$	5.3		$	(10.6	)	$	76.9
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions		0			(24.5	)		0			(8.6	)		(0.7	)		0			(33.8	)
Loan to related party		0			0			0			0			(11.7	)		0			(11.7	)
(Loans to) repayments from affiliates		0			1.2			16.7			0			(0.3	)		(17.6	)		0
Net cash proceeds from divestitures and asset sales		0			0.7			0			0.1			0			0			0.8
Net cash used in investing activities		0			(22.6	)		16.7			(8.5	)		(12.7	)		(17.6	)		(44.7	)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0			6.3			0			(0.9	)		0			0			5.4
Borrowings (repayments) of affiliated long-term debt		0			(19.2	)		(1.2	)		(3.5	)		6.3			17.6			0
Deferred financing costs		0			(0.5	)		0			0			0			0			(0.5	)
Dividends paid		(18.2	)		(2.5	)		0			(8.1	)		0			10.6			(18.2	)
Net cash provided by (used in) financing activities		(18.2	)		(15.9	)		(1.2	)		(12.5	)		6.3			28.2			(13.3	)
Effect of exchange rates on cash		0			0.1			0			(0.4	)		0.2			0			(0.1	)
Net increase (decrease) in cash and cash equivalents		0			(8.4	)		0			28.1			(0.9	)		0			18.8
Cash and cash equivalents at beginning of year		0			8.4			0			17			9.9			0			35.3
Cash and cash equivalents at end of period	$	0		$	0		$	0		$	45.1		$	9		$	0		$	54.1

Schedule_II_Valuation_and_Qual

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2013
Valuation And Qualifying Accounts [Abstract]	'
Schedule II - Valuation and Qualifying Accounts	'
	SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS
	For the years ended December 31, 2013, 2012 and 2011
		Balance at		Increase			Net			Currency			Balance
		Beginning		(Decrease)			(Write-			Translation			at End
		of Year		to Expense			Offs)						of Year
							Recoveries
	(Dollars in millions)
	2013
	Allowance for doubtful accounts	$	3.7	$	(0.2	)	$	0		$	0.1		$	3.6
	Inventory obsolescence reserves	$	1.1	$	0.7		$	0		$	(0.1	)	$	1.7
	Deferred tax valuation allowance	$	17.4	$	2.6		$	(0.2	)	$	(0.1	)	$	19.7
	2012
	Allowance for doubtful accounts	$	0.3	$	3.2		$	0		$	0.2		$	3.7
	Inventory obsolescence reserves	$	1.4	$	0.5		$	(0.8	)	$	0		$	1.1
	Deferred tax valuation allowance	$	10.2	$	8.8		$	(1.6	)	$	0		$	17.4
	2011
	Allowance for doubtful accounts	$	0.1	$	0.3		$	(0.1	)	$	0		$	0.3
	Inventory obsolescence reserves	$	2.1	$	4.2		$	(4.9	)	$	0		$	1.4
	Deferred tax valuation allowance	$	11.4	$	(1.2	)	$	0		$	0		$	10.2

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Basis of Presentation	'
	Basis of presentation – The consolidated financial statements include the accounts of the Company and all majority-owned subsidiaries for which the Company is deemed to exercise control over its operations. All significant intercompany transactions have been eliminated in consolidation. The Company’s investments in 20 percent to 50 percent-owned companies in which it has the ability to exercise significant influence over operating and financial policies are accounted for using the equity method of accounting. Accordingly, the Company’s share of the earnings of these companies is included in the accompanying consolidated statement of income. Certain prior period amounts in the consolidated financial statements and notes thereto have been reclassified to conform to the current period’s presentation.
Use of Estimates	'
	Use of estimates – Accounting principles generally accepted in the U.S. require management to make estimates and judgments that affect the reported amounts of assets and liabilities and the disclosure of contingencies on the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Estimates have been prepared on the basis of the most current and best available information and actual results could differ materially from these estimates.
Foreign Currency Translation	'
	Foreign currency translation – For consolidated entities outside of the U.S. that prepare financial statements in currencies other than the U.S. dollar, results of operations and cash flows are translated at average exchange rates during the period, and asset and liabilities are translated at end-of-period exchange rates. Cumulative translation adjustments are included as a separate component of accumulated other comprehensive loss in shareholders’ equity.
	Foreign currency transaction gains and losses result from transactions denominated in a currency which is different than the currency used by the entity to prepare its financial statements. Foreign currency transaction losses were $0.5 million, $1.7 million and $0.5 million for the years ended December 31, 2013, 2012 and 2011, respectively.
Revenue Recognition	'
	Revenue recognition – The Company recognizes revenue when the risks and rewards of ownership and title to the product have transferred to the customer. Revenue recognition generally occurs at the point of shipment; however in certain circumstances as shipping terms dictate, revenue is recognized at the point of destination. Shipping and handling costs are included as a component of cost of sales.
	The Company recognizes revenue related to the procurement of certain untreated railroad crossties upon transfer of title to the customer, which occurs upon delivery to the Company’s plant and acceptance by the customer. Service revenue, consisting primarily of wood treating services, is recognized at the time the service is provided. Payment on sales of untreated railroad crossties and wood treating services are generally due within 30 days of the invoice date. The Company’s recognition of revenue with respect to untreated crossties meets all the recognition criteria of Securities and Exchange Commission Staff Accounting Bulletin Topic 13.A.3., including transfer of title and risk of ownership, the existence of fixed purchase commitments and delivery schedules established by the customer, and the completion of all performance obligations by the Company. Revenue recognized for untreated crosstie sales for the years ended December 31, 2013, 2012 and 2011 amounted to $108.3 million, $109.0 million and $116.5 million, respectively.
Research & Development	'
	Research & development – Research and development costs are expensed as incurred and are included in selling, general and administrative expenses. These costs totaled $2.4 million in 2013, $2.3 million in 2012 and $1.9 million in 2011.
Cash and Cash Equivalents	'
	Cash and cash equivalents – Cash and cash equivalents include cash on hand and on deposit and investments in highly liquid investments with an original maturity of 90 days or less.
Accounts Receivable	'
	Accounts receivable – The Company maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments. In circumstances where the Company becomes aware of a specific customer’s inability to meet its financial obligations to Koppers, a specific reserve for bad debts is recorded against amounts due. If the financial condition of the Company’s customers were to deteriorate, resulting in an inability to make payments, additional allowances may be required.
Inventories	'
	Inventories – Inventories are carried at lower of cost or market on a worldwide basis. In the U.S., inventory cost (excluding miscellaneous types of inventory) is determined primarily utilizing the last-in, first-out (“LIFO”) basis. Inventory cost outside the U.S. is determined utilizing the first-in, first-out (“FIFO”) basis. Market represents replacement cost for raw materials and net realizable value for work in process and finished goods. LIFO inventories constituted approximately 62 percent of the FIFO inventory value at December 31, 2013 and 2012.
Property, Plant & Equipment	'
	Property, plant & equipment – Property, plant and equipment are recorded at purchased cost and include improvements which significantly increase capacities or extend useful lives of existing plant and equipment. Depreciation expense is calculated by applying the straight-line method over estimated useful lives. Estimated useful lives for buildings generally range from 10 to 20 years and depreciable lives for machinery and equipment generally range from 3 to 10 years. Net gains and losses related to asset disposals are recognized in earnings in the period in which the disposal occurs. Routine repairs, replacements and maintenance are expensed as incurred.
	The Company periodically evaluates whether current facts and circumstances indicate that the carrying value of its depreciable long-lived assets may not be recoverable. If an asset, or logical grouping of assets, is determined to be impaired, the asset is written down to its fair value using discounted future cash flows and, if available, quoted market prices.
Goodwill & Other Intangible Assets	'
	Goodwill & other intangible assets – Goodwill and other purchased intangible assets are included in the identifiable assets of the business segment to which they have been assigned. The Company performs impairment tests annually for goodwill, and more often as circumstances require. When it is determined that impairment has occurred, an appropriate charge to earnings is recorded. The Company performed its annual impairment test in the fourth quarters of 2013 and 2012 and determined that the estimated fair values substantially exceeded the carrying values of all the reporting units and accordingly, there was no impairment of goodwill.
	Identifiable intangible assets, other than goodwill, are recorded at cost. Identifiable intangible assets that do not have indefinite lives are amortized on a straight-line basis over their estimated useful lives.
Deferred Income Taxes	'
	Deferred income taxes – Deferred tax assets and liabilities are recognized for future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. The effect on deferred tax assets and liabilities of a change in tax laws is recognized in earnings in the period the new laws are enacted. A valuation allowance is recorded to reduce the carrying amounts of deferred tax assets unless it is more likely than not that such assets will be realized. Deferred tax liabilities have not been recognized for the undistributed earnings of certain foreign subsidiaries because management intends to permanently reinvest such earnings in foreign operations.
Self-insured Liabilities	'
	Self-insured liabilities – The Company is self-insured for property, casualty and workers’ compensation exposures up to various stop-loss coverage amounts. Losses are accrued based upon the Company’s estimates of the liability for the related deductibles of claims incurred. Such estimates utilize actuarial methods based on various assumptions, which include but are not limited to, the Company’s historical loss experience and projected loss development factors. In 2013 and 2012, reversals of self-insured liabilities occurred as a result of favorable loss trends related to self-insured claims.
		2013			2012
	(Dollars in millions)
	Self-insured liabilities at beginning of year	$	7.6		$	7.4
	Expense		2.5			2.4
	Reversal of self-insured liabilities		(0.4	)		(1.0	)
	Cash expenditures		(1.3	)		(1.2	)
	Self-insured liabilities at end of year	$	8.4		$	7.6
Derivative Financial Instruments	'
	Derivative financial instruments – The Company uses forward exchange contracts to hedge exposure to currency exchange rate changes on transactions and other commitments denominated in a foreign currency. Contracts are generally written on a short-term basis and are not held for trading or speculative purposes. The Company recognizes the fair value of the forward contracts as an asset or liability at each reporting date. Because the Company has not elected to designate the forward exchange contracts for hedge accounting treatment, changes in the fair value of the forward exchange contracts are recognized immediately in earnings.
Asset Retirement Obligations	'
	Asset retirement obligations – Asset retirement obligations are initially recorded at fair value and are capitalized as part of the cost of the related long-lived asset when sufficient information is available to estimate fair value. The capitalized costs are subsequently charged to depreciation expense over the estimated useful life of the related long-lived asset. The fair value of the obligation is determined by calculating the discounted value of expected future cash flows and accretion expense is recorded each month to ultimately increase this obligation to full value.
	The Company recognizes asset retirement obligations for the removal and disposal of residues; dismantling of certain tanks required by governmental authorities; cleaning and dismantling costs for owned rail cars; cleaning costs for leased rail cars and barges; and site demolition.
	The following table describes changes to the Company’s asset retirement obligation liabilities at December 31, 2013 and 2012:
		2013			2012
	(Dollars in millions)
	Asset retirement obligation at beginning of year	$	21.5		$	21.3
	Accretion expense		1.2			1.1
	Revision in estimated cash flows		6.7			1.8
	Cash expenditures		(5.6	)		(3.0	)
	Currency translation		(0.6	)		0.3
	Asset retirement obligation at end of year	$	23.2		$	21.5
Litigation & Contingencies	'
	Litigation & contingencies – Amounts associated with litigation and contingencies are accrued when management, after taking into consideration the facts and circumstances of each matter including any settlement offers, has determined that it is probable that a liability has been incurred and the amount of loss can be reasonably estimated. Legal costs for litigation are expensed as incurred with the exception of legal fees relating the CERCLA sites.
Other Current Assets	'
	Other current assets – Included in other current assets are prepaid expenses totaling $17.3 million and $7.4 million at December 31, 2013 and 2012, respectively.
Environmental Liabilities	'
	Environmental liabilities – The Company accrues for remediation costs and penalties when the responsibility to remediate is probable and the amount of related cost is reasonably estimable. If only a range of potential liability can be estimated and no amount within the range is more probable than another, the accrual is recorded at the low end of that range. Remediation liabilities are discounted if the amount and timing of the cash disbursements are readily determinable.
Deferred Revenue from Extended Product Warranty Liabilities	'
	Deferred revenue 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 describes changes to the Company’s deferred revenue at December 31, 2013 and 2012:
		2013			2012
	(Dollars in millions)
	Deferred revenue at beginning of year	$	3.9		$	4.8
	Revenue earned		(0.7	)		(0.9	)
	Deferred revenue at end of year	$	3.2		$	3.9
Stock-based Compensation	'
	Stock-based compensation – The Company records compensation cost over the vesting period for share-based payments to employees at an amount equivalent to the grant date fair value of the stock award. No compensation cost is recognized for any stock awards that are forfeited in the event the recipient fails to meet the vesting requirements.
Recently-Enacted Tax Regulations	'
	Recently-Enacted Tax Regulations
	On September 13, 2013, Treasury and the Internal Revenue Service issued final regulations regarding the deduction and capitalization of expenditures related to tangible property. The final regulations under Internal Revenue Code Sections 162, 167 and 263(a) apply to amounts paid to acquire, produce, or improve tangible property as well as dispositions of such property and are generally effective for tax years beginning on or after January 1, 2014. We have evaluated these regulations and determined they do not have a material impact on our consolidated results of operations, cash flows or financial position.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Summary of Self-Insured Liabilities	'
	Company’s historical loss experience and projected loss development factors. In 2013 and 2012, reversals of self-insured liabilities occurred as a result of favorable loss trends related to self-insured claims.
		2013			2012
	(Dollars in millions)
	Self-insured liabilities at beginning of year	$	7.6		$	7.4
	Expense		2.5			2.4
	Reversal of self-insured liabilities		(0.4	)		(1.0	)
	Cash expenditures		(1.3	)		(1.2	)
	Self-insured liabilities at end of year	$	8.4		$	7.6
Summary of Asset Retirement Obligation Liabilities	'
	The following table describes changes to the Company’s asset retirement obligation liabilities at December 31, 2013 and 2012:
		2013			2012
	(Dollars in millions)
	Asset retirement obligation at beginning of year	$	21.5		$	21.3
	Accretion expense		1.2			1.1
	Revision in estimated cash flows		6.7			1.8
	Cash expenditures		(5.6	)		(3.0	)
	Currency translation		(0.6	)		0.3
	Asset retirement obligation at end of year	$	23.2		$	21.5
Summary of Changes to Deferred Revenue	'
	The following table describes changes to the Company’s deferred revenue at December 31, 2013 and 2012:
		2013			2012
	(Dollars in millions)
	Deferred revenue at beginning of year	$	3.9		$	4.8
	Revenue earned		(0.7	)		(0.9	)
	Deferred revenue at end of year	$	3.2		$	3.9

Discontinued_Operations_Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2013
Discontinued Operations And Disposal Groups [Abstract]	'
Summary of Restructuring Activities and Related Reserves	'
	Details of the restructuring activities and related reserves for 2013 and 2012 are as follows:
		Severance		Environmental			Inventory			Site			Other			Total
		and		remediation			writedowns			demolition
		employee
		benefits
	(Dollars in millions)
	Reserve at January 1, 2012	$	1.8	$	6.7		$	0		$	6.2		$	1.2		$	15.9
	Charges		0.1		0			0.4			0			0			0.5
	Costs charged against assets		0		0			(0.4	)		0			0			(0.4	)
	Reversal of accrued charges		0		0			0			0			(0.6	)		(0.6	)
	Cash paid		-1.7		(0.1	)		0			(0.4	)		(0.5	)		(2.7	)
	Currency translation		0		0.1			0			0.1			0			0.2
	Reserve at December 31, 2012	$	0.2	$	6.7		$	0		$	5.9		$	0.1		$	12.9
	Reversal of accrued charges		-0.1		0			0			(0.3	)		0			(0.4	)
	Cash paid		0		(0.1	)		0			(2.0	)		(0.1	)		(2.2	)
	Currency translation		0		(1.0	)		0			(0.7	)		0			(1.7	)
	Reserve at December 31, 2013		$0.10	$	5.6		$	0		$	2.9		$	0		$	8.6

Earnings_and_Dividends_per_Com1

Earnings and Dividends per Common Share (Tables)	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Schedule of Basic and Diluted Earnings Per Common Share	'
	The following table sets forth the computation of basic and diluted earnings per common share:
		Year Ended December 31,
		2013			2012			2011
	(Dollars in millions, except share amounts, in thousands, and per share amounts)
	Net income attributable to Koppers	$	40.4		$	65.6		$	36.9
	Less: discontinued operations		(0.1	)		(0.1	)		(19.9	)
	Income from continuing operations attributable to Koppers	$	40.5		$	65.7		$	56.8
	Weighted average common shares outstanding:
	Basic		20,575			20,681			20,599
	Effect of dilutive securities		240			246			234
	Diluted		20,815			20,927			20,833
	Earnings per common share – continuing operations:
	Basic earnings per common share	$	1.96		$	3.18		$	2.75
	Diluted earnings per common share		1.94			3.14			2.72
	Other data:
	Antidilutive securities excluded from computation of diluted earnings per common share		240			194			106

Stockbased_Compensation_Tables

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Summary of Performance Stock Units	'
	The following table shows a summary of the performance stock units as of December 31, 2013:
	Performance Period	Minimum				Target				Maximum
		Shares				Shares				Shares
	2012 – 2014		0				95,956				143,934
	2013 – 2015		0				93,523				140,285
Summary of Status and Activity of Non-Vested Stock Awards	'
	The following table shows a summary of the status and activity of non-vested stock awards for the year ended December 31, 2013:
		Restricted				Performance				Total				Weighted Average
		Stock Units				Stock Units				Stock Units				Grant Date Fair
														Value per Unit
	Non-vested at January 1, 2013		136,098				268,677				404,775			$	36.11
	Granted		62,276				97,318				159,594			$	42.64
	Credited from dividends		3,526				7,064				10,590			$	35.17
	Performance stock unit adjustment		0				43,921				43,921			$	40.09
	Vested		(46,314	)			(85,798	)			(132,112	)		$	29.81
	Forfeited		(6,750	)			(11,198	)			(17,948	)		$	40.26
	Non-vested at December 31, 2013		148,836				319,984				468,820			$	40.3
Stock Options Fair Value Assumptions	'
	In accordance with accounting standards, compensation expense for non-vested stock options is recorded over the vesting period based on the fair value at the date of grant. The fair value of stock options on the date of grant is calculated using the Black-Scholes-Merton model and the assumptions listed below:
				February 2013 Grant				February 2012 Grant				February 2011 Grant
	Grant date price per share of option award			$	42.76			$	38.21			$	40.26
	Expected dividend yield per share				2.75	%			2.75	%			2.5	%
	Expected life in years				6.5				6.5				6.5
	Expected volatility				53.77	%			55.06	%			60	%
	Risk-free interest rate				1.29	%			1.34	%			3.02	%
	Grant date fair value per share of option awards			$	17.28			$	15.82			$	19.28
Summary of Status and Activity of Stock Options	'
	The following table shows a summary of the status and activity of stock options for the year ended December 31, 2013:
		Options				Weighted Average				Weighted Average				Aggregate Intrinsic
						Exercise Price				Remaining				Value (in millions)
						per Option				Contractual Term
										(in years)
	Outstanding at January 1, 2013		331,799			$	34.07
	Granted		94,532			$	42.76
	Exercised		(5,251	)		$	39.04
	Outstanding at December 31, 2013		421,080			$	35.96				6.86			$	4.1
	Exercisable at December 31, 2013		167,565			$	29.15				4.7			$	2.8
Schedule of Stock-based Compensation Expense Recognized	'
	Total stock-based compensation expense recognized for the three years ended December 31, 2013 is as follows:
		Year Ended December 31,
		2013				2012				2011
	(Dollars in millions)
	Stock-based compensation expense recognized:
	Selling, general and administrative expenses	$	4.3			$	6.9			$	5.3
	Less related income tax benefit		1.7				2.8				2
	Decrease in net income attributable to Koppers	$	2.6			$	4.1			$	3.3

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Summary of Income Tax Provision	'
	Components of the Company’s income tax provision from continuing operations are as follows:
		Years Ended December 31,
		2013			2012			2011
	(Dollars in millions)
	Current:
	Federal	$	3.5		$	15.7		$	24.7
	State		0.6			1.3			1.1
	Foreign		14			8.6			21.5
	Total current tax provision		18.1			25.6			47.3
	Deferred:
	Federal		16.4			4.9			(6.7	)
	State		2.5			(1.2	)		0.1
	Foreign		(0.2	)		4			(2.0	)
	Total deferred tax provision (benefit)		18.7			7.7			(8.6	)
	Total income tax provision	$	36.8		$	33.3		$	38.7
Summary of Income Taxes Reconciled with Federal Statutory Rate	'
	The provision for income taxes is reconciled with the federal statutory rate as follows:
		Years Ended December 31,
		2013			2012			2011
	Federal income tax rate		35	%		35	%		35	%
	State income taxes, net of federal tax benefit		2.1			(0.5	)		0.7
	Foreign earnings taxed at different rates		15.5			0.5			1.4
	Domestic production activities deduction		(2.0	)		(2.7	)		(1.3	)
	Non-deductible fines and penalties		0			0			0.2
	Deferred tax adjustments		(0.2	)		(0.3	)		0.1
	Change in tax contingency reserves		(1.5	)		1.2			3.8
	Foreign tax credits		(1.1	)		(0.6	)		0
	Other		0			0.5			0.3
			47.8	%		33.1	%		40.2	%
Summary of Deferred Tax Assets and Liabilities	'
	Significant components of the Company’s deferred tax assets and liabilities are as follows:
		December 31,
		2013			2012
	(Dollars in millions)
	Deferred tax assets:
	Reserves, including insurance, environmental and deferred revenue	$	16.5		$	19.8
	Pension and other postretirement benefits obligations		10.3			33.4
	Tax credits		10.3			9.6
	Net operating loss benefit		10			9.4
	Accrued employee compensation		9.4			9.8
	Asset retirement obligations		6.8			7.2
	Book/tax inventory accounting differences		3.3			3
	Capital loss benefit		1.1			1.5
	Other		2.2			3.1
	Valuation allowance		(19.7	)		(17.4	)
	Total deferred tax assets		50.2			79.4
	Deferred tax liabilities:
	Tax over book depreciation and amortization		34.1			29.5
	Unremitted earnings of foreign subsidiaries		6.8			5.9
	Tax/book inventory accounting differences		1.1			1.1
	Other		3.7			3.7
	Total deferred tax liabilities		45.7			40.2
	Net deferred tax assets	$	4.5		$	39.2
Summary of Unrecognized Tax Benefits	'
	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:
		December 31,
		2013			2012			2011
	(Dollars in millions)
	Balance at beginning of year	$	7.7		$	9.9		$	6.5
	Additions based on tax provisions related to the current year		0.4			0.5			4
	Additions for tax provisions of prior years		0.4			1.3			0
	Reductions of tax provisions of prior years		(0.8	)		(0.5	)		0
	Reductions as a result of payments and settlements		(1.1	)		(2.8	)		0
	Reductions as a result of a lapse of the applicable statute of limitations		(0.5	)		(0.7	)		(0.6	)
	Balance at end of year	$	6.1		$	7.7		$	9.9

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Summary of Results of Segment Operations	'
	Results of Segment Operations
			Year Ended December 31,
			2013			2012			2011
	(Dollars in millions)
	Revenues from external customers:
	Carbon Materials and Chemicals		$	906.1		$	999.7		$	943.1
	Railroad and Utility Products and Services			572.2			555.3			523.1
	Total		$	1,478.30		$	1,555.00		$	1,466.20
	Intersegment revenues:
	Carbon Materials and Chemicals		$	94.2		$	106.5		$	95.2
	Depreciation & amortization(a):
	Carbon Materials and Chemicals		$	18.2		$	16.9		$	17.4
	Railroad and Utility Products and Services			11.5			10.7			9.5
	Total		$	29.7		$	27.6		$	26.9
	Operating profit:
	Carbon Materials and Chemicals		$	43.9		$	83.1		$	89.1
	Railroad and Utility Products and Services			58.3			45.1			34.8
	Corporate(b)			(1.9	)		(1.6	)		(1.2	)
	Total		$	100.3		$	126.6		$	122.7
	Capital expenditures (including acquisitions):
	Carbon Materials and Chemicals		$	58		$	17.3		$	23
	Railroad and Utility Products and Services			15.9			25			10.2
	Corporate			1.3			0.6			0.6
	Total		$	75.2		$	42.9		$	33.8
	(a)	Excludes impairment charges of $11.9 million in 2013 for Carbon Materials and Chemicals and $0.6 million in 2012 for Railroad and Utility Products and Services.
	(b)	Operating loss for Corporate includes general and administrative costs for Koppers Holdings Inc, the parent company of Koppers Inc.
Summary of Assets and Goodwill by Segment	'
	Assets and Goodwill by Segment
			December 31,
			2013			2012
	(Dollars in millions)
	Assets:
	Carbon Materials and Chemicals		$	535.5		$	516.3
	Railroad and Utility Products and Services			179.3			205
	Segment assets			714.8			721.3
	Cash & cash equivalents			30			4.8
	Income tax receivable			9			1.6
	Deferred taxes			13.3			35.5
	Deferred financing costs			7.2			7.2
	Property, plant and equipment, net			3.8			3.5
	Deferred charges			2.6			2.6
	Other			4.2			3.5
	Total		$	784.9		$	780
	Goodwill:
	Carbon Materials and Chemicals		$	68		$	70.2
	Railroad and Utility Products and Services			4.7			5.4
	Total		$	72.7		$	75.6
Schedule of Revenues and Long-Lived Assets by Geographic Area	'
	Revenues and Long-lived Assets by Geographic Area
			Year			Revenue			Long-lived
									assets
	(Dollars in millions)
	United States			2013		$	782.5		$	169.1
				2012			827.6			162.9
				2011			787.5			161.6
	Australasia			2013			348.3			100.6
				2012			318.9			72.4
				2011			276.6			58.7
	Europe			2013			225.1			32.8
				2012			247.8			36.3
				2011			248			35.7
	Other countries			2013			122.4			0
				2012			160.7			0
				2011			154.1			0
	Total			2013		$	1,478.30		$	302.5
				2012		$	1,555.00		$	271.6
				2011		$	1,466.20		$	256
Schedule of Segment Revenues for Significant Product Lines	'
	Segment Revenues for Significant Product Lines
			Year Ended December 31,
			2013			2012			2011
	(Dollars in millions)
	Carbon Materials and Chemicals:
	Carbon pitch		$	384.7		$	442.4		$	431.1
	Creosote and carbon black feedstock			228.2			233.8			162
	Phthalic anhydride			98.6			120			112.4
	Naphthalene			64.5			60.3			72.3
	Other products			130.1			143.2			165.3
				906.1			999.7			943.1
	Railroad and Utility Products and Services:
	Railroad crossties			331.1			341.1			324.9
	Utility poles			119.3			101.3			84.2
	Creosote			61.4			57			52.7
	Rail joint bars			24.5			25.6			24.7
	Other products			35.9			30.3			36.6
				572.2			555.3			523.1
	Total		$	1,478.30		$	1,555.00		$	1,466.20

Inventories_Tables

Inventories (Tables)	12 Months Ended
	Dec. 31, 2013
Inventory Disclosure [Abstract]	'
Components of Inventories	'
	Inventories as of December 31, 2013 and 2012 were as follows:
		December 31,
		2013		2012
	(Dollars in millions)
	Raw materials	$	105.4	$	118.2
	Work in process		19.2		20
	Finished goods		94.8		109.7
			219.4		247.9
	Less revaluation to LIFO		50.6		52.1
	Net	$	168.8	$	195.8

Equity_Investments_Tables

Equity Investments (Tables)	12 Months Ended
	Dec. 31, 2013
Equity Method Investments And Joint Ventures [Abstract]	'
Equity Earnings (Losses) and Dividends Received	'
	Equity in earnings for the three years ended December 31, 2013 were as follows:
		Equity income
	(Dollars in millions)
	2013	$	0.8
	2012		0.8
	2011		0.2

Property_Plant_and_Equipment_T

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2013
Property Plant And Equipment [Abstract]	'
Property, Plant and Equipment	'
	Property, plant and equipment as of December 31, 2013 and 2012 were as follows:
		December 31,
		2013		2012
	(Dollars in millions)
	Land	$	9.1	$	7
	Buildings		30.6		31.7
	Machinery and equipment		608.1		543.1
			647.8		581.8
	Less accumulated depreciation		450.8		420.7
	Net	$	197	$	161.1

Goodwill_and_Other_Identifiabl1

Goodwill and Other Identifiable Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Changes in Carrying Amount of Goodwill	'
	The change in the carrying amount of goodwill attributable to each business segment for the years ended December 31, 2013 and December 31, 2012 was as follows:
		Carbon Materials and			Railroad and			Total
		Chemicals			Utility Products
					and Services
	(Dollars in millions)
	Balance at December 31, 2011	$	69.4		$	2.7		$	72.1
	Acquisitions		0			2.6			2.6
	Currency translation		0.8			0.1			0.9
	Balance at December 31, 2012	$	70.2		$	5.4		$	75.6
	Currency translation		(2.2	)		(0.7	)		(2.9	)
	Balance at December 31, 2013	$	68		$	4.7		$	72.7
Schedule of Identifiable Intangible Assets	'
	The Company’s identifiable intangible assets with finite lives are being amortized over their estimated useful lives and are summarized below:
		December 31,
		2013									2012
		Gross			Accumulated			Net			Gross		Accumulated		Net
		Carrying			Amortization						Carrying		Amortization
		Amount									Amount
	(Dollars in millions)
	Customer contracts	$	19.8		$	9.7		$	10.1		$	20.9	$	8.1	$	12.8
	Supply contracts		2.9			1.1			1.8			2.8		0.8		2
	Non-compete agreements		1.6			1.3			0.3			1.7		1.2		0.5
	Favorable lease agreements		0.8			0.8			0			0.8		0.8		0
	Total	$	25.1		$	12.9		$	12.2		$	26.2	$	10.9	$	15.3
Schedule of Future Amortization Expense	'
	Estimated amortization expense for the next five years is summarized below:
		Estimated
		annual
		amortization
	(Dollars in millions)
	2014	$	1.8
	2015		1.8
	2016		1.3
	2017		1.1
	2018		1.1

Debt_Tables

Debt (Tables)	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Schedule of Long-Term Debt Instruments	'
	Debt at December 31, 2013 and December 31, 2012 was as follows:
							December 31,
		Weighted			Maturity		2013		2012
		Average
		Interest Rate
	(Dollars in millions, except interest rates)
	Revolving credit facility		0.00%			2018	$	0	$	0
	Construction loans		6.24%			2018		6.6		0
	Senior Notes		7 7/8%			2019		296.5		296.1
	Total debt							303.1		296.1
	Less short-term debt and current maturities of long-term debt							0		0
	Long-term debt (excluding current portion)						$	303.1	$	296.1
Schedule of Debt Maturities	'
	At December 31, 2013 the aggregate debt maturities for the next five years are as follows:
	(Dollars in millions)
	2014	$	0
	2015		0
	2016		1
	2017		2.3
	2018		3.3
	Thereafter		300
	Total maturities		306.6
	Future accretion on Senior Notes		(3.5	)
	Total debt	$	303.1

Leases_Tables

Leases (Tables)	12 Months Ended
	Dec. 31, 2013
Leases [Abstract]	'
Future Minimum Commitments for Operating Leases	'
	Future minimum commitments for operating leases having non-cancelable lease terms in excess of one year are as follows:
	(Dollars in millions)
	2014	$	37
	2015		21.2
	2016		16.4
	2017		14
	2018		12.3
	Thereafter		30
	Total	$	130.9

Pensions_and_Postretirement_Be1

Pensions and Post-retirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2013
Compensation And Retirement Disclosure [Abstract]	'
Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans	'
	Net periodic pension costs for 2013, 2012 and 2011 were as follows:
		December 31,
		Pension Benefits									Other Benefits
		2013			2012			2011			2013			2012		2011
	(Dollars in millions)
	Components of net periodic benefit cost:
	Service cost	$	3.4		$	3.5		$	3.3		$	0.1		$	0.1	$	0.2
	Interest cost		10.7			10.7			11.1			0.5			0.5		0.6
	Expected return on plan assets		(12.5	)		(10.7	)		(11.0	)		0			0		0
	Amortization of prior service cost		0.1			0.1			0.1			0			0		(0.1	)
	Amortization of net loss		7.6			8.1			6.3			(0.1	)		0		0
	Amortization of transition asset		0			(0.3	)		(0.3	)		0			0		0
	Settlements and curtailments		0.1			0.3			0.2			0			0		0
	Net periodic benefit cost	$	9.4		$	11.7		$	9.7		$	0.5		$	0.6	$	0.7
Schedule of Change in Funded Status of Pension and Post-Retirement Plans	'
	The change in the funded status of the pension and postretirement plans as of December 31, 2013 and December 31, 2012 is as follows:
		December 31,
		Pension Benefits						Other Benefits
		2013			2012			2013			2012
	(Dollars in millions)
	Change in benefit obligation:
	Benefit obligation at beginning of year	$	255.2		$	239.5		$	11.2		$	12.5
	Service cost		3.4			3.5			0.1			0.1
	Interest cost		10.7			10.7			0.5			0.5
	Plan participants’ contributions		0.2			0.2			0			0
	Actuarial (gains) losses		(18.6	)		10.3			(1.3	)		(1.8	)
	Plan amendments		(1.5	)		0			0			0
	Settlements		(0.9	)		(1.4	)		0			0
	Currency translation		0.2			2.4			0			0
	Benefits paid		(10.9	)		(10.0	)		(0.1	)		(0.1	)
	Benefit obligation at end of year		237.8			255.2			10.4			11.2
	Change in plan assets:
	Fair value of plan assets at beginning of year		175.6			146.6			0			0
	Actual return on plan assets		19.2			15.7			0			0
	Employer contribution		22.5			22.4			0.1			0.1
	Plan participants’ contributions		0.2			0.2			0			0
	Settlements		(0.9	)		(1.4	)		0			0
	Currency translation		0			2.1			0			0
	Benefits paid		(10.9	)		(10.0	)		(0.1	)		(0.1	)
	Fair value of plan assets at end of year		205.7			175.6			0			0
	Funded status of the plan	$	(32.1	)	$	(79.6	)	$	(10.4	)	$	(11.2	)
	Amounts recognized in the balance sheet consist of:
	Noncurrent assets	$	0.6		$	0.2		$	0		$	0
	Current liabilities		0.7			0.4			0.8			0.7
	Noncurrent liabilities		32			79.4			9.6			10.5
	Pension plans with benefit obligations in excess of plan assets:
	Benefit obligation	$	231.9		$	247.5
	Fair value of plan assets		199.2			167.6
	Pension plans with accumulated benefit obligations in excess of plan assets:
	Accumulated benefit obligation	$	225		$	229
	Fair value of plan assets		199.2			167.6
Schedule of Projected Benefit Payments	'
	Benefit payments for pension benefits, which are primarily funded by the pension plan assets, and other benefits, which are funded by general corporate assets and reflecting future expected service as appropriate, are expected to be paid as follows:
		Pension Benefits			Other Benefits
	(Dollars in millions)
	2014	$	11.2		$	0.8
	2015		11.7			0.8
	2016		12.6			0.8
	2017		13.5			0.9
	2018		14.5			0.9
	2019 – 2023		74.5			4
Schedule of Weighted-Average Assumptions	'
	Weighted-Average Assumptions as of December 31
		December 31,
		Pension Benefits						Other Benefits
		2013			2012			2013			2012
	Discount rate		5.06	%		4.33	%		5.25	%		4.37	%
	Expected return on plan assets		7.04			7.25
	Rate of compensation increase		3.13			3.1
	Initial medical trend rate								7.15			7.35
Schedule of Weighted Average Asset Allocation for Company's Pension Plans	'
	The weighted average asset allocation for the Company’s pension plans at December 31 by asset category is as follows:
		December 31,
		2013			2012
	Equity securities		38	%		61	%
	Debt securities		59			35
	Other		3			4
			100	%		100	%
Schedule of Pension Plan Assets at Fair Value	'
	The pension assets are all substantially held in pooled or commingled investment vehicles. The following table sets forth by level, the Company’s pension plan assets at fair value, within the fair value hierarchy, as of December 31, 2013 and December 31, 2012:
		As of December 31, 2013
		Quoted prices			Significant			Significant			Total
		in active			observable			unobservable
		markets for			inputs			inputs
		identical assets			(Level 2)			(Level 3)
		(Level 1)
	(Dollars in millions)
	U.S. equity securities	$	17.8		$	15.9		$	0			$  33.7
	International equity securities		0			44.3			0			44.3
	U.S. debt securities		24.8			64.7			0			89.5
	International debt securities		7.4			24.9			0			32.3
	Real estate and other investments		0			1.5			0			1.5
	Cash and cash equivalents		0			4.4			0			4.4
		$	50		$	155.7		$	0			$205.70
		As of December 31, 2012
		Quoted prices			Significant			Significant			Total
		in active			observable			unobservable
		markets for			inputs			inputs
		identical assets			(Level 2)			(Level 3)
		(Level 1)
	(Dollars in millions)
	U.S. equity securities	$	0		$	80		$	0			$  80.0
	International equity securities		0			27.2			0			27.2
	U.S. debt securities		0			36.4			0			36.4
	International debt securities		0			24.5			0			24.5
	Real estate and other investments		0			1.7			0			1.7
	Cash and cash equivalents		0			5.8			0			5.8
		$	0		$	175.6		$	0			$175.60
Schedule of Health Care Cost Trend Rates	'
	A one-percentage-point change in the assumed health care cost trend rate would have the following effects:
		1% Increase			1% Decrease
	(Dollars in millions)
	Increase (decrease) from change in health care cost trend rates:
	Postretirement benefit expense	$	0		$	0
	Postretirement benefit liability		0.2			(0.2	)

Common_Stock_and_Senior_Conver1

Common Stock and Senior Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2013
Text Block [Abstract]	'
Schedule of Changes in Senior Convertible Preferred Stock, Common Stock and Treasury Stock	'
	Changes in senior convertible preferred stock, common stock and treasury stock for the three years ended December 31, 2013 are as follows:
		Year Ended December 31,
		2013			2012			2011
	(Shares in thousands)
	Senior Convertible Preferred Stock:
	Balance at beginning and end of year		0			0			0
	Common Stock:
	Balance at beginning of year		21,585			21,309			21,278
	Issued for employee stock plans		137			276			31
	Balance at end of year		21,722			21,585			21,309
	Treasury Stock:
	Balance at beginning of year		(951	)		(706	)		(700	)
	Shares repurchased		(439	)		(245	)		(6	)
	Balance at end of year		(1,390	)		(951	)		(706	)

Fair_Value_of_Financial_Instru1

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Schedule of Company's Financial Instruments	'
	Carrying amounts and the related estimated fair values of the Company’s financial instruments as of December 31, 2013 and 2012 are as follows:
			December 31, 2013				December 31, 2012
			Fair Value		Carrying		Fair Value		Carrying
					Value				Value
	(Dollars in millions)
	Financial assets:
	Cash and cash equivalents		$	82.2	$	82.2	$	66.7	$	66.7
	Investments and other assets(a)			1.4		1.4		1.4		1.4
	Financial liabilities:
	Long-term debt (including current portion)		$	331.2	$	303.1	$	331.1	$	296.1
	(a)	Excludes equity method investments.

Commitments_and_Contingent_Lia1

Commitments and Contingent Liabilities (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Changes in Accrued Liability for Environmental Matters	'
	Environmental Reserves Rollforward. The following table reflects changes in the accrued liability for environmental matters, of which $8.2 million and $8.5 million are classified as current liabilities at December 31, 2013 and 2012, respectively:
		Year Ended December 31,
		2013			2012
	(Dollars in millions)
	Balance at beginning of year		$14.10			$17.70
	Expense		1.8			1
	Reversal of reserves		(1.2	)		(0.4	)
	Cash expenditures		(0.9	)		(4.6	)
	Currency translation		(1.9	)		0.4
	Balance at end of year		$11.90			$14.10

Selected_Quarterly_Financial_D1

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Schedule of Selected Quarterly Financial Data	'
	The following is a summary of the quarterly results of operations for the years ended December 31, 2013 and 2012:
			Year Ended December 31, 2013
			1st Quarter		2nd Quarter			3rd Quarter		4th Quarter			Fiscal Year
	(Dollars in millions, except per share amounts)
	Statement of operations data:
	Net sales		$	370.4	$	370.9		$	395.2	$	341.8		$	1,478.30
	Operating profit(a)			24.9		28.5			39.1		7.8			100.3
	Income from continuing operations			11.4		14.8			19.6		(5.6	)		40.2
	Net income (loss)			11.5		14.7			19.5		(5.6	)		40.1
	Net income (loss) attributable to Koppers			11		14.4			19.1		(4.1	)		40.4
	Common stock data:
	Earnings (loss) per common share attributable to Koppers common shareholders:(b)
	Basic –
	Continuing operations		$	0.53	$	0.7		$	0.93	$	(0.20	)	$	1.96
	Discontinued operations(c)			0		(0.01	)		0		0			0
	Earnings per basic common share		$	0.53	$	0.69		$	0.93	$	(0.20	)	$	1.96
	Diluted –
	Continuing operations		$	0.53	$	0.7		$	0.92	$	(0.20	)	$	1.94
	Discontinued operations(c)			0		(0.01	)		0		0			0
	Earnings per diluted common share		$	0.53	$	0.69		$	0.92	$	(0.20	)	$	1.94
	Dividends declared per common share		$	0.25	$	0.25		$	0.25	$	0.25		$	1
	Price range of common stock:
	High		$	45.72	$	46.48		$	42.09	$	49.99		$	49.99
	Low			38.7		37.45			34.69		41.61			34.69
			Year Ended December 31, 2012
			1st Quarter		2nd Quarter			3rd Quarter		4th Quarter			Fiscal Year
	(Dollars in millions, except per share amounts)
	Statement of operations data:
	Net sales		$	380.9	$	411.3		$	387.9	$	374.9		$	1,555.00
	Operating profit			29.2		40.7			30.8		25.9			126.6
	Income from continuing operations			15.8		21.1			16.2		14.2			67.3
	Net income			15.9		20.9			16.2		14.2			67.2
	Net income attributable to Koppers			15.6		20.4			16		13.6			65.6
	Common stock data:
	Earnings (loss) per common share attributable to Koppers common shareholders:(b)
	Basic –
	Continuing operations		$	0.74	$	1		$	0.77	$	0.66		$	3.18
	Discontinued operations(c)			0.01		(0.01	)		0		0			(0.01	)
	Earnings per basic common share		$	0.75	$	0.99		$	0.77	$	0.66		$	3.17
	Diluted –
	Continuing operations		$	0.74	$	0.99		$	0.77	$	0.65		$	3.14
	Discontinued operations(c)			0.01		(0.01	)		0		0			(0.01	)
	Earnings per diluted common share		$	0.75	$	0.98		$	0.77	$	0.65		$	3.13
	Dividends declared per common share		$	0.24	$	0.24		$	0.24	$	0.24		$	0.96
	Price range of common stock:
	High		$	40.61	$	40.37		$	37.82	$	38.83		$	40.61
	Low			32.15		31.17			29.3		30.99			29.3
	(a)	In the fourth quarter of 2013, the Company recorded asset impairment charges totaling $11.9 million primarily consisting of writedowns related to the Company’s coal tar distillation facilities located in Uithoorn, the Netherlands; Tangshan, China; and Follansbee, West Virginia.
	(b)	The cumulative sum of quarterly basic and diluted net income per share amounts may not equal total basic and diluted net income per share amounts for the year due to differences in weighted average and equivalent shares outstanding for each of the periods presented.
	(c)	In the fourth quarter of 2011, the Company ceased manufacturing operations at its carbon black facility located in Kurnell, Australia. The results of operations of the carbon black facility have been reclassified to discontinued operations for all periods presented as run-off activities were completed in the first quarter of 2012.

Subsidiary_Guarantor_Informati2

Subsidiary Guarantor Information for Koppers Inc. Senior Notes (Tables)	12 Months Ended
	Dec. 31, 2013
Text Block [Abstract]	'
Condensed Consolidating Statement of Comprehensive Income	'
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	843.7		$	61.8		$	622.2		$	(49.4	)	$	1,478.30
	Cost of sales including depreciation and amortization		0			745.4			43.5			566.9			(49.5	)		1,306.30
	Selling, general and administrative		1.9			41.5			0.7			27.6			0			71.7
	Operating profit (loss)		(1.9	)		56.8			17.6			27.7			0.1			100.3
	Other income (expense)		0			1.3			4.2			2.1			(4.1	)		3.5
	Equity income of subsidiaries		41.7			17.5			11.4			0			(70.6	)		0
	Interest expense		0			26.7			0			4.2			(4.1	)		26.8
	Income taxes		(0.6	)		7.3			16.4			13.7			0			36.8
	Income from continuing operations		40.4			41.6			16.8			11.9			(70.5	)		40.2
	Discontinued operations		0			0.1			0			(0.2	)		0			(0.1	)
	Noncontrolling interests		0			0			0			(0.3	)		0			(0.3	)
	Net income attributable to Koppers	$	40.4		$	41.7		$	16.8		$	12		$	(70.5	)	$	40.4
	Comprehensive income attributable to Koppers	$	52.3		$	53.5		$	8.4		$	13.8		$	(75.7	)	$	52.3
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	893.2		$	97.5		$	638.4		$	(74.1	)	$	1,555.00
	Cost of sales including depreciation and amortization		0			786.6			78			562			(73.8	)		1,352.80
	Selling, general and administrative		1.6			45.1			2.1			26.8			0			75.6
	Operating profit (loss)		(1.6	)		61.5			17.4			49.6			(0.3	)		126.6
	Other income (expense)		0			0.4			6.1			0.6			(5.2	)		1.9
	Equity income of subsidiaries		66.6			40.8			28.8			0.1			(136.3	)		0
	Interest expense		0			27.4			0			5.8			(5.3	)		27.9
	Income taxes		(0.6	)		8.7			12.5			12.7			0			33.3
	Income from continuing operations		65.6			66.6			39.8			31.8			(136.5	)		67.3
	Discontinued operations		0			0			0			(0.1	)		0			(0.1	)
	Noncontrolling interests		0			0			0			1.6			0			1.6
	Net income attributable to Koppers	$	65.6		$	66.6		$	39.8		$	30.1		$	(136.5	)	$	65.6
	Comprehensive income attributable to Koppers	$	73.7		$	74.8		$	44		$	32.4		$	(151.2	)	$	73.7
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2011
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	854.1		$	72.6		$	585.2		$	(45.7	)	$	1,466.20
	Cost of sales including depreciation and amortization		0			762.9			55			497			(45.7	)		1,269.20
	Selling, general and administrative		1.2			41.6			1.8			29.7			0			74.3
	Operating profit (loss)		(1.2	)		49.6			15.8			58.5			0			122.7
	Other income (expense)		0			0.3			5.5			0.4			(5.5	)		0.7
	Equity income of subsidiaries		37.7			22.9			1.3			0			(61.9	)		0
	Interest expense		0			27.4			0.1			5.2			(5.5	)		27.2
	Income taxes		(0.4	)		7.7			0.8			30.6			0			38.7
	Income from continuing operations		36.9			37.7			21.7			23.1			(61.9	)		57.5
	Discontinued operations		0			0			0			(19.9	)		0			(19.9	)
	Noncontrolling interests		0			0			0			0.7			0			0.7
	Net income attributable to Koppers	$	36.9		$	37.7		$	21.7		$	2.5		$	(61.9	)	$	36.9
	Comprehensive income attributable to Koppers	$	18.9		$	19.7		$	17.3		$	(1.4	)	$	(35.6	)	$	18.9
Condensed Consolidating Balance Sheet	'
	Condensed Consolidating Balance Sheet
	December 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	29.9		$	0.1		$	52.2		$	0		$	82.2
	Receivables, net		0			75.6			9.3			82			0			166.9
	Affiliated receivables		0.2			1.1			3.9			2.3			(7.5	)		0
	Inventories, net		0			86.1			0			82.9			(0.2	)		168.8
	Deferred tax assets		0			7.9			1.5			0.6			0			10
	Other current assets		0			7.3			0.6			37.3			0			45.2
	Total current assets		0.2			207.9			15.4			257.3			(7.7	)		473.1
	Equity investments		174.7			333.5			182.9			4.6			(689.1	)		6.6
	Property, plant and equipment, net		0			112.2			0			84.8			0			197
	Goodwill		0			39.8			0			32.9			0			72.7
	Deferred tax assets		0			2.4			(1.4	)		8.3			0			9.3
	Affiliated loan receivables		0			8.5			123.8			40.9			(173.2	)		0
	Other noncurrent assets		0			15			0			11.2			0			26.2
	Total assets	$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
	LIABILITIES AND EQUITY
	Accounts payable	$	0		$	48.3		$	6.7		$	52.6		$	0		$	107.6
	Affiliated payables		0			1.9			4			8.6			(14.5	)		0
	Accrued liabilities		5.1			27.8			0.5			54.1			0			87.5
	Total current liabilities		5.1			78			11.2			115.3			(14.5	)		195.1
	Long-term debt		0			296.5			0			6.6			0			303.1
	Affiliated debt		0			109.5			8.5			55.2			(173.2	)		0
	Other long-term liabilities		0			67.6			2.5			26.8			0			96.9
	Total liabilities		5.1			551.6			22.2			203.9			(187.7	)		595.1
	Koppers shareholders’ equity		169.8			167.7			298.5			216.1			(682.3	)		169.8
	Noncontrolling interests		0			0			0			20			0			20
	Total liabilities and equity	$	174.9		$	719.3		$	320.7		$	440		$	(870.0	)	$	784.9
	Condensed Consolidating Balance Sheet
	December 31, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	4.8		$	0		$	61.9		$	0		$	66.7
	Receivables, net		0			80.2			6.3			77.8			0			164.3
	Affiliated receivables		0.7			0			119			9			(128.7	)		0
	Inventories, net		0			102.2			0			93.9			(0.3	)		195.8
	Deferred tax assets		0			9.4			5.5			0.2			0			15.1
	Other current assets		0			6.4			2.8			30.1			0			39.3
	Total current assets		0.7			203			133.6			272.9			(129.0	)		481.2
	Equity investments		154.9			648.3			183.8			3.8			(985.0	)		5.8
	Property, plant and equipment, net		0			105.7			0			55.4			0			161.1
	Goodwill		0			39.8			0			35.8			0			75.6
	Deferred tax assets		0			14.9			2.1			10.2			0			27.2
	Affiliated loan receivables		0			7.7			326.3			39.3			(373.3	)		0
	Other noncurrent assets		0			15.7			0			13.4			0			29.1
	Total assets	$	155.6		$	1,035.10		$	645.8		$	430.8		$	(1,487.3	)	$	780
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	51.4		$	1.7		$	50.3		$	0		$	103.5
	Affiliated payables		0			120.8			7.6			6.4			(134.8	)		0
	Accrued liabilities		4.9			15.9			12.2			44.7			0			77.7
	Total current liabilities		5			188.1			21.5			101.4			(134.8	)		181.2
	Long-term debt		0			296.1			0			0			0			296.1
	Affiliated debt		0			301			7.7			64.6			(373.3	)		0
	Other long-term liabilities		0			101.2			2.4			31			0			134.6
	Total liabilities		5			886.4			31.6			197			(508.1	)		611.9
Koppers shareholders’ equity		150.6			148.7			614.2			216.3			(979.2	)		150.6
Noncontrolling interests		0			0			0			17.5			0			17.5
Total liabilities and equity	$	155.6		$	1,035.10		$	645.8		$	430.8		$	(1,487.3	)	$	780
Condensed Consolidating Statement of Cash Flows	'
	Condensed Consolidating Statement of Cash Flows
	For the Year Ended December 31, 2013
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	37.8		$	278.7		$	130.1		$	47.6		$	(376.6	)	$	117.6
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(23.3	)		0			(51.9	)		0			(75.2	)
	(Loans to) repayments from affiliates		0			(0.8	)		193.2			(1.7	)		(190.7	)		0
	Net cash proceeds (payments) from divestitures and asset sales		0			1.3			0			1.6			0			2.9
	Net cash used in investing activities		0			(22.8	)		193.2			(52.0	)		(190.7	)		(72.3	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of long-term debt		0			0			0			6.6			0			6.6
	Borrowings of affiliated long-term debt		0			(191.5	)		0.8			0			190.7			0
	Deferred financing costs		0			(1.3	)		0			0			0			(1.3	)
	Dividends paid		(20.5	)		(38.5	)		(324.0	)		(14.7	)		376.6			(21.1	)
	Stock issued and repurchased		(17.3	)		0			0			0			0			(17.3	)
	Other financing receipts		0			0.5			0			2.3			0			2.8
	Net cash provided by (used in) financing activities		(37.8	)		(230.8	)		(323.2	)		(5.8	)		567.3			(30.3	)
	Effect of exchange rates on cash		0			0			0			0.5			0			0.5
	Net increase in cash and cash equivalents		0			25.1			0.1			(9.7	)		0			15.5
	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		$	29.9		$	0.1		$	52.2		$	0		$	82.2
	Condensed Consolidating Statement of Cash Flows
	For the Year Ended December 31, 2012
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	26.1		$	44.6		$	8.7		$	30.9		$	(32.5	)	$	77.8
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(21.3	)		0			(21.6	)		0			(42.9	)
	Loan repayment by related party		0			0			0			2.2			0			2.2
	(Loans to) repayments from affiliates		0			0.3			(8.4	)		(2.7	)		10.8			0
	Net cash proceeds (payments) from divestitures and asset sales		0			0.4			0			0.4			0			0.8
	Net cash used in investing activities		0			(20.6	)		(8.4	)		(21.7	)		10.8			(39.9	)
	Cash provided by (used in) financing activities:
	Repayments of long-term debt		0			(6.4	)		0			0			0			(6.4	)
	Borrowings of affiliated long-term debt		0			13.3			(0.3	)		(2.2	)		(10.8	)		0
	Deferred financing costs		0			(0.1	)		0			0			0			(0.1	)
	Dividends paid		(19.5	)		(27.6	)		0			(4.9	)		32.5			(19.5	)
	Stock issued and repurchased		(6.6	)		0			0			0			0			(6.6	)
	Other financing receipts		0			1.6			0			3.7			0			5.3
	Net cash provided by (used in) financing activities		(26.1	)		(19.2	)		(0.3	)		(3.4	)		21.7			(27.3	)
	Effect of exchange rates on cash		0			0			0			2			0			2
	Net increase in cash and cash equivalents		0			4.8			0			7.8			0			12.6
	Cash and cash equivalents at beginning of year		0			0			0			54.1			0			54.1
	Cash and cash equivalents at end of period	$	0		$	4.8		$	0		$	61.9		$	0		$	66.7
	Condensed Consolidating Statement of Cash Flows
	For the Year Ended December 31, 2011
		Parent			Koppers Inc.			Domestic			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Subsidiaries			Adjustments
								Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities		$18.20		$	30		$	(15.5	)	$	54.8		$	(10.6	)	$	76.9
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(24.5	)		0			(9.3	)		0			(33.8	)
	Loan to related party		0			0			0			(11.7	)		0			(11.7	)
	(Loans to) repayments from affiliates		0			1.2			16.7			(0.3	)		(17.6	)		0
	Net cash proceeds from divestitures and asset sales		0			0.7			0			0.1			0			0.8
	Net cash used in investing activities		0			(22.6	)		16.7			(21.2	)		(17.6	)		(44.7	)
	Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0			6.3			0			(0.9	)		0			5.4
Borrowings of affiliated long-term debt		0			(19.2	)		(1.2	)		2.8			17.6			0
Deferred financing costs		0			(0.5	)		0			0			0			(0.5	)
Dividends paid		(18.2	)		(2.5	)		0			(8.1	)		10.6			(18.2	)
Net cash provided by (used in) financing activities		(18.2	)		(15.9	)		(1.2	)		(6.2	)		28.2			(13.3	)
Effect of exchange rates on cash		0			0.1			0			(0.2	)		0			(0.1	)
Net increase (decrease) in cash and cash equivalents		0			(8.4	)		0			27.2			0			18.8
Cash and cash equivalents at beginning of year		0			8.4			0			26.9			0			35.3
Cash and cash equivalents at end of period	$	0		$	0		$	0		$	54.1		$	0		$	54.1

Subsidiary_Guarantor_Informati3

Subsidiary Guarantor Information for Shelf Registration (Tables)	12 Months Ended
	Dec. 31, 2013
Text Block [Abstract]	'
Condensed Consolidating Statement of Comprehensive Income	'
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	843.7		$	61.8		$	462.7		$	162.1		$	(52.0	)	$	1,478.30
	Cost of sales including depreciation and amortization		0			745.4			43.5			413.3			156.2			(52.1	)		1,306.30
	Selling, general and administrative		1.9			41.5			0.7			22.1			5.5			0			71.7
	Operating profit (loss)		(1.9	)		56.8			17.6			27.3			0.4			0.1			100.3
	Other income (expense)		0			1.3			4.2			0.9			1.2			(4.1	)		3.5
	Equity income (loss) of subsidiaries		41.7			17.5			11.4			(1.3	)		0			(69.3	)		0
	Interest expense		0			26.7			0			3.2			1			(4.1	)		26.8
	Income taxes		(0.6	)		7.3			16.4			12.2			1.5			0			36.8
	Income from continuing operations		40.4			41.6			16.8			11.5			(0.9	)		(69.2	)		40.2
	Discontinued operations		0			0.1			0			(0.2	)		0			0			(0.1	)
	Noncontrolling interests		0			0			0			0			(0.3	)		0			(0.3	)
	Net income attributable to Koppers	$	40.4		$	41.7		$	16.8		$	11.3		$	(0.6	)	$	(69.2	)	$	40.4
	Comprehensive income attributable to Koppers	$	52.3		$	53.5		$	8.4		$	10.1		$	0.4		$	(72.4	)	$	52.3
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2012
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	893.2		$	97.5		$	480		$	158.6		$	(74.3	)	$	1,555.00
	Cost of sales including depreciation and amortization		0			786.6			78			414.6			147.6			(74.0	)		1,352.80
	Selling, general and administrative		1.6			45.1			2.1			23.4			3.4			0			75.6
	Operating profit (loss)		(1.6	)		61.5			17.4			42			7.6			(0.3	)		126.6
	Other income (expense)		0			0.4			6.1			0.2			0.4			(5.2	)		1.9
	Equity income of subsidiaries		66.6			40.8			28.8			1.4			0			(137.6	)		0
	Interest expense		0			27.4			0			4.2			1.5			(5.2	)		27.9
	Income taxes		(0.6	)		8.7			12.5			10.5			2.2			0			33.3
	Income from continuing operations		65.6			66.6			39.8			28.9			4.3			(137.9	)		67.3
	Discontinued operations		0			0			0			(0.1	)		0			0			(0.1	)
	Noncontrolling interests		0			0			0			0			1.6			0			1.6
	Net income attributable to Koppers	$	65.6		$	66.6		$	39.8		$	28.8		$	2.7		$	(137.9	)	$	65.6
	Comprehensive income attributable to Koppers	$	73.7		$	74.8		$	44		$	31.5		$	2.8		$	(153.1	)	$	73.7
	Condensed Consolidating Statement of Comprehensive Income
	For the Year Ended December 31, 2011
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Net sales	$	0		$	854.1		$	72.6		$	443.6		$	147		$	(51.1	)	$	1,466.20
	Cost of sales including depreciation and amortization		0			762.9			55			364.2			138.2			(51.1	)		1,269.20
	Selling, general and administrative		1.2			41.6			1.8			26.2			3.5			0			74.3
	Operating profit (loss)		(1.2	)		49.6			15.8			53.2			5.3			0			122.7
	Other income (expense)		0			0.3			5.5			0.1			0.3			(5.5	)		0.7
	Equity income of subsidiaries		37.7			22.9			1.3			1.4			0			(63.3	)		0
	Interest expense		0			27.4			0.1			4.8			0.5			(5.6	)		27.2
	Income taxes		(0.4	)		7.7			0.8			28.7			1.9			0			38.7
	Income from continuing operations		36.9			37.7			21.7			21.2			3.2			(63.2	)		57.5
	Discontinued operations		0			0			0			(19.9	)		0			0			(19.9	)
	Noncontrolling interests		0			0			0			0			0.7			0			0.7
	Net income attributable to Koppers	$	36.9		$	37.7		$	21.7		$	1.3		$	2.5		$	(63.2	)	$	36.9
	Comprehensive income attributable to Koppers	$	18.9		$	19.7		$	17.3		$	(3.7	)	$	3.5		$	(36.8	)	$	18.9
Condensed Consolidating Balance Sheet	'
	Condensed Consolidating Balance Sheet
	December 31, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	29.9		$	0.1		$	43.5		$	8.7		$	0		$	82.2
	Receivables, net		0			75.6			9.3			55.5			26.5			0			166.9
	Affiliated receivables		0.2			1.1			3.9			0.8			1.6			(7.6	)		0
	Inventories, net		0			86.1			0			75.2			7.7			(0.2	)		168.8
	Deferred tax assets		0			7.9			1.5			0			0.6			0			10
	Other current assets		0			7.3			0.6			17.5			19.8			0			45.2
	Total current assets		0.2			207.9			15.4			192.5			64.9			(7.8	)		473.1
	Equity investments		174.7			333.5			182.9			50.5			4.5			(739.5	)		6.6
	Property, plant and equipment, net		0			112.2			0			38.1			46.7			0			197
	Goodwill		0			39.8			0			31.5			1.4			0			72.7
	Deferred tax assets		0			2.4			(1.4	)		5.5			2.8			0			9.3
	Affiliated loan receivables		0			8.5			123.8			0.1			40.8			(173.2	)		0
	Other noncurrent assets		0			15			0			9.9			1.3			0			26.2
	Total assets	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
	LIABILITIES AND EQUITY
	Accounts payable	$	0		$	48.3		$	6.7		$	40.6		$	12		$	0		$	107.6
	Affiliated payables		0			1.9			4			0.4			8.4			(14.7	)		0
	Accrued liabilities		5.1			27.8			0.5			31.4			22.7			0			87.5
	Total current liabilities		5.1			78			11.2			72.4			43.1			(14.7	)		195.1
	Long-term debt		0			296.5			0			0			6.6			0			303.1
	Affiliated debt		0			109.5			8.5			55.2			0			(173.2	)		0
	Other long-term liabilities		0			67.6			2.5			19.6			7.2			0			96.9
	Total liabilities		5.1			551.6			22.2			147.2			56.9			(187.9	)		595.1
	Koppers shareholders’ equity		169.8			167.7			298.5			180.9			85.5			(732.6	)		169.8
	Noncontrolling interests		0			0			0			0			20			0			20
	Total liabilities and equity	$	174.9		$	719.3		$	320.7		$	328.1		$	162.4		$	(920.5	)	$	784.9
	Condensed Consolidating Balance Sheet
	December 31, 2012
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	ASSETS
	Cash and cash equivalents	$	0		$	4.8		$	0		$	40.7		$	21.2		$	0		$	66.7
	Receivables, net		0			80.2			6.3			63.5			14.3			0			164.3
	Affiliated receivables		0.7			0			119			2.3			6.9			(128.9	)		0
	Inventories, net		0			102.2			0			86.7			7.2			(0.3	)		195.8
	Deferred tax assets		0			9.4			5.5			0			0.2			0			15.1
	Other current assets		0			6.4			2.8			17.6			12.5			0			39.3
	Total current assets		0.7			203			133.6			210.8			62.3			(129.2	)		481.2
	Equity investments		154.9			648.3			183.8			43			4			(1,028.2	)		5.8
	Property, plant and equipment, net		0			105.7			0			40.7			14.7			0			161.1
	Goodwill		0			39.8			0			34.4			1.4			0			75.6
	Deferred tax assets		0			14.9			2.1			7.6			2.6			0			27.2
	Affiliated loan receivables		0			7.7			326.3			0.1			39.2			(373.3	)		0
	Other noncurrent assets		0			15.7			0			12.1			1.3			0			29.1
	Total assets	$	155.6		$	1,035.10		$	645.8		$	348.7		$	125.5		$	(1,530.7	)	$	780
	LIABILITIES AND EQUITY
	Accounts payable	$	0.1		$	51.4		$	1.7		$	40.6		$	9.7		$	0		$	103.5
	Affiliated payables		0			120.8			7.6			1.4			8.9			(138.7	)		0
	Accrued liabilities		4.9			15.9			12.2			35.8			8.9			0			77.7
	Total current liabilities		5			188.1			21.5			77.8			27.5			(138.7	)		181.2
	Long-term debt		0			296.1			0			0			0			0			296.1
	Affiliated debt		0			301			7.7			64.5			0			(373.2	)		0
	Other long-term liabilities		0			101.2			2.4			24.5			6.5			0			134.6
	Total liabilities		5			886.4			31.6			166.8			34			(511.9	)		611.9
Koppers shareholders’ equity		150.6			148.7			614.2			181.9			74			(1,018.8	)		150.6
Noncontrolling interests		0			0			0			0			17.5			0			17.5
Total liabilities and equity	$	155.6		$	1,035.10		$	645.8		$	348.7		$	125.5		$	(1,530.7	)	$	780
Condensed Consolidating Statement of Cash Flows	'
	Condensed Consolidating Statement of Cash Flows
	For the Year Ended December 31, 2013
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	37.8		$	278.7		$	130.1		$	39.9		$	7.7		$	(376.6	)	$	117.6
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(23.3	)		0			(22.1	)		(37.5	)		7.7			(75.2	)
	(Loans to) repayments from affiliates		0			(0.8	)		193.2			0			(1.7	)		(190.7	)		0
	Net cash proceeds from divestitures and asset sales		0			1.3			0			1.1			0.5			0			2.9
	Net cash provided by (used in) investing activities		0			(22.8	)		193.2			(21.0	)		(38.7	)		(183.0	)		(72.3	)
	Cash provided by (used in) financing activities:
	Borrowings (repayments) of long-term debt		0			0			0			0			6.6			0			6.6
	Borrowings of affiliated long-term debt		0			(191.5	)		0.8			0			0			190.7			0
	Deferred financing costs		0			(1.3	)		0			0			0			0			(1.3	)
	Dividends paid		(20.5	)		(38.5	)		(324.0	)		(14.1	)		(0.6	)		376.6			(21.1	)
	Stock issued and repurchased		(17.3	)		0			0			0			7.7			(7.7	)		(17.3	)
	Other financing receipts		0			0.5			0			0			2.3			0			2.8
	Net cash provided by (used in) financing activities		(37.8	)		(230.8	)		(323.2	)		(14.1	)		16			559.6			(30.3	)
	Effect of exchange rates on cash		0			0			0			(2.0	)		2.5			0			0.5
	Net increase (decrease) in cash and cash equivalents		0			25.1			0.1			2.8			(12.5	)		0			15.5
	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		$	29.9		$	0.1		$	43.5		$	8.7		$	0		$	82.2
	Condensed Consolidating Statement of Cash Flows
	For the Year Ended December 31, 2012
		Parent			Koppers Inc.			Domestic			Foreign			Non-Guarantor			Consolidating			Consolidated
								Guarantor			Guarantor			Subsidiaries			Adjustments
								Subsidiaries			Subsidiaries
	(Dollars in millions)
	Cash provided by (used in) operating activities	$	26.1		$	44.6		$	8.7		$	29.5		$	1.4		$	(32.5	)	$	77.8
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(21.3	)		0			(31.5	)		(0.5	)		10.4			(42.9	)
	Loan repayment by related party		0			0			0			0			2.2			0			2.2
	(Loans to) repayments from affiliates		0			0.3			(8.4	)		0			(2.7	)		10.8			0
	Net cash proceeds from divestitures and asset sales		0			0.4			0			0.4			0			0			0.8
	Net cash provided by (used in) investing activities		0			(20.6	)		(8.4	)		(31.1	)		(1.0	)		21.2			(39.9	)
	Cash provided by (used in) financing activities:
	Repayments of long-term debt		0			(6.4	)		0			0			0			0			(6.4	)
	Borrowings of affiliated long-term debt		0			13.3			(0.3	)		0			(2.2	)		(10.8	)		0
	Deferred financing costs		0			(0.1	)		0			0			0			0			(0.1	)
	Dividends paid		(19.5	)		(27.6	)		0			(4.9	)		0			32.5			(19.5	)
	Stock issued and repurchased		(6.6	)		0			0			0			10.4			(10.4	)		(6.6	)
	Other financing receipts		0			1.6			0			0			3.7			0			5.3
	Net cash provided by (used in) financing activities		(26.1	)		(19.2	)		(0.3	)		(4.9	)		11.9			11.3			(27.3	)
	Effect of exchange rates on cash		0			0			0			2.1			(0.1	)		0			2
	Net increase (decrease) in cash and cash equivalents		0			4.8			0			(4.4	)		12.2			0			12.6
	Cash and cash equivalents at beginning of year		0			0			0			45.1			9			0			54.1
	Cash and cash equivalents at end of period	$	0		$	4.8		$	0		$	40.7		$	21.2		$	0		$	66.7
	Condensed Consolidating Statement of Cash Flows
	For the Year Ended December 31, 2011
		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	$	18.2		$	30		$	(15.5	)	$	49.5		$	5.3		$	(10.6	)	$	76.9
	Cash provided by (used in) investing activities:
	Capital expenditures and acquisitions		0			(24.5	)		0			(8.6	)		(0.7	)		0			(33.8	)
	Loan to related party		0			0			0			0			(11.7	)		0			(11.7	)
	(Loans to) repayments from affiliates		0			1.2			16.7			0			(0.3	)		(17.6	)		0
	Net cash proceeds from divestitures and asset sales		0			0.7			0			0.1			0			0			0.8
	Net cash used in investing activities		0			(22.6	)		16.7			(8.5	)		(12.7	)		(17.6	)		(44.7	)
	Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0			6.3			0			(0.9	)		0			0			5.4
Borrowings (repayments) of affiliated long-term debt		0			(19.2	)		(1.2	)		(3.5	)		6.3			17.6			0
Deferred financing costs		0			(0.5	)		0			0			0			0			(0.5	)
Dividends paid		(18.2	)		(2.5	)		0			(8.1	)		0			10.6			(18.2	)
Net cash provided by (used in) financing activities		(18.2	)		(15.9	)		(1.2	)		(12.5	)		6.3			28.2			(13.3	)
Effect of exchange rates on cash		0			0.1			0			(0.4	)		0.2			0			(0.1	)
Net increase (decrease) in cash and cash equivalents		0			(8.4	)		0			28.1			(0.9	)		0			18.8
Cash and cash equivalents at beginning of year		0			8.4			0			17			9.9			0			35.3
Cash and cash equivalents at end of period	$	0		$	0		$	0		$	45.1		$	9		$	0		$	54.1

Description_of_Business_Additi

Description of Business - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2013
	Segment
Collaboration Arrangement Disclosure [Abstract]	'
Number of operating segment	2

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary Of Significant Accounting Policies [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Equity method investment, ownership percentage	30.00%	'	'	'	'	'	'	'	30.00%	'	'
Foreign currency transaction losses	'	'	'	'	'	'	'	'	$500,000	$1,700,000	$500,000
Period for payment of approval basis sale	'	'	'	'	'	'	'	'	'30 days	'	'
Net sales	341,800,000	395,200,000	370,900,000	370,400,000	374,900,000	387,900,000	411,300,000	380,900,000	1,478,300,000	1,555,000,000	1,466,200,000
Research and development costs	'	'	'	'	'	'	'	'	2,400,000	2,300,000	1,900,000
Maximum maturity period for highly liquid investment	'	'	'	'	'	'	'	'	'90 days	'	'
Percentage of LIFO inventory	62.00%	'	'	'	62.00%	'	'	'	62.00%	62.00%	'
Impairment of goodwill	0	'	'	'	0	'	'	'	'	'	'
Prepaid expenses	17,300,000	'	'	'	7,400,000	'	'	'	17,300,000	7,400,000	'
Untreated Crosstie Sales [Member]	'	'	'	'	'	'	'	'	'	'	'
Summary Of Significant Accounting Policies [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	$108,300,000	$109,000,000	$116,500,000
Minimum [Member]	'	'	'	'	'	'	'	'	'	'	'
Summary Of Significant Accounting Policies [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Equity method investment, ownership percentage	20.00%	'	'	'	'	'	'	'	20.00%	'	'
Minimum [Member] | Buildings [Member]	'	'	'	'	'	'	'	'	'	'	'
Summary Of Significant Accounting Policies [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Estimated useful lives	'	'	'	'	'	'	'	'	'10 years	'	'
Minimum [Member] | Machinery and Equipment [Member]	'	'	'	'	'	'	'	'	'	'	'
Summary Of Significant Accounting Policies [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Estimated useful lives	'	'	'	'	'	'	'	'	'3 years	'	'
Maximum [Member]	'	'	'	'	'	'	'	'	'	'	'
Summary Of Significant Accounting Policies [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Equity method investment, ownership percentage	50.00%	'	'	'	'	'	'	'	50.00%	'	'
Maximum [Member] | Buildings [Member]	'	'	'	'	'	'	'	'	'	'	'
Summary Of Significant Accounting Policies [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Estimated useful lives	'	'	'	'	'	'	'	'	'20 years	'	'
Maximum [Member] | Machinery and Equipment [Member]	'	'	'	'	'	'	'	'	'	'	'
Summary Of Significant Accounting Policies [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Estimated useful lives	'	'	'	'	'	'	'	'	'10 years	'	'

Summary_of_Significant_Account4

Summary of Significant Accounting Policies - Summary of Self-lnsured Liabilities (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]	'	'
Self-insured liabilities at beginning of year	$7.60	$7.40
Expense	2.5	2.4
Reversal of self-insured liabilities	-0.4	-1
Cash expenditures	-1.3	-1.2
Self-insured liabilities at end of year	$8.40	$7.60

Summary_of_Significant_Account5

Summary of Significant Accounting Policies - Summary of Asset Retirement Obligation Liabilities (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Regulatory Assets [Abstract]	'	'
Asset retirement obligation at beginning of year	$21.50	$21.30
Accretion expense	1.2	1.1
Revision in estimated cash flows	6.7	1.8
Cash expenditures	-5.6	-3
Currency translation	-0.6	0.3
Asset retirement obligation at end of year	$23.20	$21.50

Summary_of_Significant_Account6

Summary of Significant Accounting Policies - Summary of Changes to Deferred Revenue (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Movement In Deferred Revenue [Roll Forward]	'	'
Deferred revenue at beginning of year	$3.90	$4.80
Revenue earned	-0.7	-0.9
Deferred revenue at end of year	$3.20	$3.90

Business_Acquisitions_Addition

Business Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended		0 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Jan. 20, 2014	Nov. 19, 2012
			Subsequent Event [Member]	Western Poles [Member]
Business Acquisition [Line Items]	'	'	'	'
Business acquisition cash	'	'	'	$13.80
Amount payable assuming certain sales contracts	'	'	'	4.9
Acquisition amount payment period	'	'	'	'36 months
Pro forma revenue	1,581.70	1,480.30	'	'
Pro forma operating profit	130.1	123.7	'	'
Adjustment for working capital	'	'	0.8	'
Purchase price subject to post-closing adjustments	'	'	$29.60	'

Discontinued_Operations_Additi

Discontinued Operations - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Discontinued Operations And Disposal Groups [Abstract]	'	'	'	'
Costs related to closure	$41	'	'	'
Estimated total future closure costs	'	0.5	'	'
Future completion period, closure	'	'2015	'	'
Net sales from discontinued operation	'	'	5.6	72.7
Operating loss from discontinued operation	'	($0.20)	($0.30)	($43.70)

Discontinued_Operations_Summar

Discontinued Operations - Summary of Restructuring Activities and Related Reserves (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	$12.90	$15.90
Charges	'	0.5
Costs charged against assets	'	-0.4
Reversal of accrued charges	-0.4	-0.6
Cash paid	-2.2	-2.7
Currency translation	-1.7	0.2
Reserve, Ending Balance	8.6	12.9
Severance and Employee Benefits [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	0.2	1.8
Charges	'	0.1
Costs charged against assets	'	0
Reversal of accrued charges	-0.1	0
Cash paid	0	-1.7
Currency translation	0	0
Reserve, Ending Balance	0.1	0.2
Environmental Remediation [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	6.7	6.7
Charges	'	0
Costs charged against assets	'	0
Reversal of accrued charges	0	0
Cash paid	-0.1	-0.1
Currency translation	-1	0.1
Reserve, Ending Balance	5.6	6.7
Inventory Writedowns [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	0	0
Charges	'	0.4
Costs charged against assets	'	-0.4
Reversal of accrued charges	0	0
Cash paid	0	0
Currency translation	0	0
Reserve, Ending Balance	0	0
Site Demolition [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	5.9	6.2
Charges	'	0
Costs charged against assets	'	0
Reversal of accrued charges	-0.3	0
Cash paid	-2	-0.4
Currency translation	-0.7	0.1
Reserve, Ending Balance	2.9	5.9
Other [Member]	'	'
Restructuring Cost and Reserve [Line Items]	'	'
Reserve, Beginning Balance	0.1	1.2
Charges	'	0
Costs charged against assets	'	0
Reversal of accrued charges	0	-0.6
Cash paid	-0.1	-0.5
Currency translation	0	0
Reserve, Ending Balance	$0	$0.10

Earnings_Per_Common_Share_Sche

Earnings Per Common Share - Schedule of Basic and Diluted Earnings Per Common Share (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Net income attributable to Koppers	($4.10)	$19.10	$14.40	$11	$13.60	$16	$20.40	$15.60	$40.40	$65.60	$36.90
Less: discontinued operations	'	'	'	'	'	'	'	'	-0.1	-0.1	-19.9
Income from continuing operations attributable to Koppers	'	'	'	'	'	'	'	'	$40.50	$65.70	$56.80
Weighted average common shares outstanding:	'	'	'	'	'	'	'	'	'	'	'
Basic	'	'	'	'	'	'	'	'	20,575	20,681	20,599
Effect of dilutive securities	'	'	'	'	'	'	'	'	240	246	234
Diluted	'	'	'	'	'	'	'	'	20,815	20,927	20,833
Earnings per common share - continuing operations:	'	'	'	'	'	'	'	'	'	'	'
Basic earnings per common share	($0.20)	$0.93	$0.70	$0.53	$0.66	$0.77	$1	$0.74	$1.96	$3.18	$2.75
Diluted earnings per common share	($0.20)	$0.92	$0.70	$0.53	$0.65	$0.77	$0.99	$0.74	$1.94	$3.14	$2.72
Other data:	'	'	'	'	'	'	'	'	'	'	'
Antidilutive securities excluded from computation of diluted earnings per common share	'	'	'	'	'	'	'	'	240	194	106

Earnings_Per_Common_Share_Addi

Earnings Per Common Share - Additional Information (Detail) (USD $)

3 Months Ended

12 Months Ended

0 Months Ended

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Feb. 05, 2014

Subsequent Event [Member]

Schedule Of Earnings Per Share Basic And Diluted [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Dividends declared per common share

$0.25

$0.25

$0.25

$0.25

$0.24

$0.24

$0.24

$0.24

$1

$0.96

$0.88

$0.25

Common share, dividend payable date

'

'

'

'

'

'

'

'

7-Apr-14

'

'

'

Common share, dividend declared date

'

'

'

'

'

'

'

'

5-Feb-14

'

'

'

Common share, dividend record date

'

'

'

'

'

'

'

'

18-Feb-14

'

'

'

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2011
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, vesting period in years	'3 years	'
Stock options, term in years	'10 years	'
Future compensation expense related to non-vested stock-based compensation arrangements	4	'
Future compensation expense, weighted-average expected period of recognition in months	'19 months	'
Performance Stock Units [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Performance stock unit granted in years	'3 years	'2 years
Number of vest performance stock unit, if performance criteria are not achieved	0	'
Minimum [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Percentage of target award the participants earn	0.00%	'
Maximum [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Percentage of target award the participants earn	150.00%	'
Restricted Stock Units [Member]	'	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'	'
Stock options, vesting period in years	'1 year	'

StockBased_Compensation_Summar

Stock-Based Compensation - Summary of Performance Stock Units (Detail)	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	468,820	404,775
Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	319,984	268,677
Minimum Shares [Member] | 2012 - 2014 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	0	'
Minimum Shares [Member] | 2013 - 2015 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	0	'
Target Shares [Member] | 2012 - 2014 [Member] | Performance Stock Units [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of shares outstanding	95,956	'
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	93,523	'
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	143,934	'
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	140,285	'

StockBased_Compensation_Summar1

Stock-Based Compensation - Summary of Status and Activity of Non-Vested Stock Awards (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	404,775
Granted	159,594
Credited from dividends	10,590
Performance stock unit adjustment	43,921
Vested	-132,112
Forfeited	-17,948
Non-vested, Ending Balance	468,820
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit	$36.11
Granted, Weighted Average Grant Date Fair Value per Unit	$42.64
Credited from dividends, Weighted Average Grant Date Fair Value per Unit	$35.17
Performance stock unit adjustment, Weighted Average Grant Date Fair Value per Unit	$40.09
Vested, Weighted Average Grant Date Fair Value per Unit	$29.81
Forfeited, Weighted Average Grant Date Fair Value per Unit	$40.26
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit	$40.30
Restricted Stock Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	136,098
Granted	62,276
Credited from dividends	3,526
Performance stock unit adjustment	0
Vested	-46,314
Forfeited	-6,750
Non-vested, Ending Balance	148,836
Performance Stock Units [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Non-vested, Beginning Balance	268,677
Granted	97,318
Credited from dividends	7,064
Performance stock unit adjustment	43,921
Vested	-85,798
Forfeited	-11,198
Non-vested, Ending Balance	319,984

StockBased_Compensation_Stock_

Stock-Based Compensation - Stock Options Fair Value Assumptions (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013
February 2013 Grant [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Grant date price per share of option award	$42.76
Expected dividend yield per share	2.75%
Expected life in years	'6 years 6 months
Expected volatility	53.77%
Risk-free interest rate	1.29%
Grant date fair value per share of option awards	$17.28
February 2012 Grant [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Grant date price per share of option award	$38.21
Expected dividend yield per share	2.75%
Expected life in years	'6 years 6 months
Expected volatility	55.06%
Risk-free interest rate	1.34%
Grant date fair value per share of option awards	$15.82
February 2011 Grant [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Grant date price per share of option award	$40.26
Expected dividend yield per share	2.50%
Expected life in years	'6 years 6 months
Expected volatility	60.00%
Risk-free interest rate	3.02%
Grant date fair value per share of option awards	$19.28

StockBased_Compensation_Summar2

Stock-Based Compensation - Summary of Status and Activity of Stock Options (Detail) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Options Outstanding, Beginning Balance	331,799
Options, Granted	94,532
Options, Exercised	-5,251
Options Outstanding, Ending Balance	421,080
Options Exercisable, Ending Balance	167,565
Outstanding, Weighted Average Exercise Price per Option, Beginning Balance	$34.07
Granted, Weighted Average Exercise Price per Option	$42.76
Exercised, Weighted Average Exercise Price per Option	$39.04
Outstanding, Weighted Average Exercise Price per Option, Ending Balance	$35.96
Exercisable, Weighted Average Exercise Price per Option, Ending Balance	$29.15
Outstanding at December 31, 2013, Weighted Average Remaining Contractual Term	'6 years 10 months 10 days
Exercisable at December 31, 2013, Weighted Average Remaining Contractual Term	'4 years 8 months 12 days
Outstanding at December 31, 2013, Aggregate Intrinsic Value	$4.10
Exercisable at December 31, 2013, Aggregate Intrinsic Value	$2.80

StockBased_Compensation_Schedu

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Stock-based compensation expense recognized:	'	'	'
Selling, general and administrative expenses	$4.30	$6.90	$5.30
Less related income tax benefit	1.7	2.8	2
Decrease in net income attributable to Koppers	$2.60	$4.10	$3.30

Income_Taxes_Summary_of_Income

Income Taxes - Summary of Income Tax Provision (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current:	'	'	'
Federal	$3.50	$15.70	$24.70
State	0.6	1.3	1.1
Foreign	14	8.6	21.5
Total current tax provision	18.1	25.6	47.3
Deferred:	'	'	'
Federal	16.4	4.9	-6.7
State	2.5	-1.2	0.1
Foreign	-0.2	4	-2
Total deferred tax provision (benefit)	18.7	7.7	-8.6
Total income tax provision	$36.80	$33.30	$38.70

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax [Line Items]	'	'	'
Income before income taxes	$24.60	$42.60	$51.80
Employee post-retirement benefit plans	13.5	2.2	-9.3
Income tax benefit related to restricted stock and stock options	0.5	1.6	'
Valuation allowance, operating loss carryforwards	7.2	'	'
Valuation allowance, capital loss	1.1	'	'
Expiration of foreign tax credits	'2018	'	'
Valuation allowance on foreign tax credits	9.4	'	'
Unrecognized tax benefits	4.5	5.5	'
Interest expense and related penalties	-0.1	0.3	0.2
Accrued interest expense and penalties	1.2	1.3	'
State [Member]	'	'	'
Income Tax [Line Items]	'	'	'
Net operating losses	9.1	'	'
State [Member] | Maximum [Member]	'	'	'
Income Tax [Line Items]	'	'	'
Operating losses expiration	'2032	'	'
State [Member] | Minimum [Member]	'	'	'
Income Tax [Line Items]	'	'	'
Operating losses expiration	'2015	'	'
Foreign [Member]	'	'	'
Income Tax [Line Items]	'	'	'
Valuation allowance, operating loss carryforwards	1.7	'	'
Net operating losses	0.9	'	'
Operating losses expiration	'2019	'	'
Foreign Subsidiary [Member]	'	'	'
Income Tax [Line Items]	'	'	'
Undistributed earnings	$103	'	'

Income_Taxes_Summary_of_Income1

Income Taxes - Summary of Income Taxes Reconciled with Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
Federal income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefit	2.10%	-0.50%	0.70%
Foreign earnings taxed at different rates	15.50%	0.50%	1.40%
Domestic production activities deduction	-2.00%	-2.70%	-1.30%
Non-deductible fines and penalties	0.00%	0.00%	0.20%
Deferred tax adjustments	-0.20%	-0.30%	0.10%
Change in tax contingency reserves	-1.50%	1.20%	3.80%
Foreign tax credits	-1.10%	-0.60%	0.00%
Other	0.00%	0.50%	0.30%
Total effective tax rate	47.80%	33.10%	40.20%

Income_Taxes_Summary_of_Deferr

Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Deferred tax assets:	'	'
Reserves, including insurance, environmental and deferred revenue	$16.50	$19.80
Pension and other postretirement benefits obligations	10.3	33.4
Tax credits	10.3	9.6
Net operating loss benefit	10	9.4
Accrued employee compensation	9.4	9.8
Asset retirement obligations	6.8	7.2
Book/tax inventory accounting differences	3.3	3
Capital loss benefit	1.1	1.5
Other	2.2	3.1
Valuation allowance	-19.7	-17.4
Total deferred tax assets	50.2	79.4
Deferred tax liabilities:	'	'
Tax over book depreciation and amortization	34.1	29.5
Unremitted earnings of foreign subsidiaries	6.8	5.9
Tax/book inventory accounting differences	1.1	1.1
Other	3.7	3.7
Total deferred tax liabilities	45.7	40.2
Net deferred tax assets	$4.50	$39.20

Income_taxes_Summary_of_Unreco

Income taxes - Summary of Unrecognized Tax Benefits (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
Balance at beginning of year	$7.70	$9.90	$6.50
Additions based on tax provisions related to the current year	0.4	0.5	4
Additions for tax provisions of prior years	0.4	1.3	0
Reductions of tax provisions of prior years	-0.8	-0.5	0
Reductions as a result of payments and settlements	-1.1	-2.8	0
Reductions as a result of a lapse of the applicable statute of limitations	-0.5	-0.7	-0.6
Balance at end of year	$6.10	$7.70	$9.90

Segment_Information_Additional

Segment Information - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
									Segment
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Number of reportable segments	'	'	'	'	'	'	'	'	2	'	'
Revenues from non-U.S. countries	$341.80	$395.20	$370.90	$370.40	$374.90	$387.90	$411.30	$380.90	$1,478.30	$1,555	$1,466.20
Non-U.S. Countries [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenues from non-U.S. countries	'	'	'	'	'	'	'	'	$695.80	$727.40	$681.10

Segment_Information_Summary_of

Segment Information - Summary of Results of Segment Operations (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues from external customers:	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers	$341.80	$395.20	$370.90	$370.40	$374.90	$387.90	$411.30	$380.90	$1,478.30	$1,555	$1,466.20
Intersegment revenues:	'	'	'	'	'	'	'	'	'	'	'
Intersegment revenues	341.8	395.2	370.9	370.4	374.9	387.9	411.3	380.9	1,478.30	1,555	1,466.20
Depreciation & amortization(a):	'	'	'	'	'	'	'	'	'	'	'
Depreciation and amortization expense	'	'	'	'	'	'	'	'	29.7	27.6	26.9
Operating profit:	'	'	'	'	'	'	'	'	'	'	'
Operating profit (loss)	7.8	39.1	28.5	24.9	25.9	30.8	40.7	29.2	100.3	126.6	122.7
Capital expenditures (including acquisitions):	'	'	'	'	'	'	'	'	'	'	'
Capital expenditures (including acquisitions)	'	'	'	'	'	'	'	'	75.2	42.9	33.8
Carbon Materials and Chemicals [Member]	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers:	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers	'	'	'	'	'	'	'	'	906.1	999.7	943.1
Intersegment revenues:	'	'	'	'	'	'	'	'	'	'	'
Intersegment revenues	'	'	'	'	'	'	'	'	906.1	999.7	943.1
Railroad and Utility Products and Services [Member]	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers:	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers	'	'	'	'	'	'	'	'	572.2	555.3	523.1
Intersegment revenues:	'	'	'	'	'	'	'	'	'	'	'
Intersegment revenues	'	'	'	'	'	'	'	'	572.2	555.3	523.1
Operating Segments [Member] | Carbon Materials and Chemicals [Member]	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers:	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers	'	'	'	'	'	'	'	'	906.1	999.7	943.1
Intersegment revenues:	'	'	'	'	'	'	'	'	'	'	'
Intersegment revenues	'	'	'	'	'	'	'	'	906.1	999.7	943.1
Depreciation & amortization(a):	'	'	'	'	'	'	'	'	'	'	'
Depreciation and amortization expense	'	'	'	'	'	'	'	'	18.2	16.9	17.4
Operating profit:	'	'	'	'	'	'	'	'	'	'	'
Operating profit (loss)	'	'	'	'	'	'	'	'	43.9	83.1	89.1
Capital expenditures (including acquisitions):	'	'	'	'	'	'	'	'	'	'	'
Capital expenditures (including acquisitions)	'	'	'	'	'	'	'	'	58	17.3	23
Operating Segments [Member] | Railroad and Utility Products and Services [Member]	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers:	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers	'	'	'	'	'	'	'	'	572.2	555.3	523.1
Intersegment revenues:	'	'	'	'	'	'	'	'	'	'	'
Intersegment revenues	'	'	'	'	'	'	'	'	572.2	555.3	523.1
Depreciation & amortization(a):	'	'	'	'	'	'	'	'	'	'	'
Depreciation and amortization expense	'	'	'	'	'	'	'	'	11.5	10.7	9.5
Operating profit:	'	'	'	'	'	'	'	'	'	'	'
Operating profit (loss)	'	'	'	'	'	'	'	'	58.3	45.1	34.8
Capital expenditures (including acquisitions):	'	'	'	'	'	'	'	'	'	'	'
Capital expenditures (including acquisitions)	'	'	'	'	'	'	'	'	15.9	25	10.2
Intersegment [Member] | Carbon Materials and Chemicals [Member]	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers:	'	'	'	'	'	'	'	'	'	'	'
Revenues from external customers	'	'	'	'	'	'	'	'	94.2	106.5	95.2
Intersegment revenues:	'	'	'	'	'	'	'	'	'	'	'
Intersegment revenues	'	'	'	'	'	'	'	'	94.2	106.5	95.2
Corporate, Non-Segment [Member]	'	'	'	'	'	'	'	'	'	'	'
Operating profit:	'	'	'	'	'	'	'	'	'	'	'
Operating profit (loss)	'	'	'	'	'	'	'	'	-1.9	-1.6	-1.2
Capital expenditures (including acquisitions):	'	'	'	'	'	'	'	'	'	'	'
Capital expenditures (including acquisitions)	'	'	'	'	'	'	'	'	$1.30	$0.60	$0.60

Segment_Information_Summary_of1

Segment Information - Summary of Results of Segment Operations (Parenthetical) (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenue from External Customer [Line Items]	'	'	'	'
Impairment charges	$11.90	$11.90	$0.60	$0
Carbon Materials and Chemicals [Member]	'	'	'	'
Revenue from External Customer [Line Items]	'	'	'	'
Impairment charges	'	11.9	'	'
Railroad and Utility Products and Services [Member]	'	'	'	'
Revenue from External Customer [Line Items]	'	'	'	'
Impairment charges	'	'	$0.60	'

Segment_Information_Summary_of2

Segment Information - Summary of Tangible and Intangible Assets by Segment (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Millions, unless otherwise specified
Assets:	'	'	'	'
Cash & cash equivalents	$82.20	$66.70	$54.10	$35.30
Income tax receivable	9	1.6	'	'
Deferred taxes	50.2	79.4	'	'
Deferred financing costs	7.2	7.2	'	'
Property, plant and equipment, net	197	161.1	'	'
Segment assets	784.9	780	'	'
Goodwill:	'	'	'	'
Goodwill	72.7	75.6	72.1	'
Operating Segments [Member]	'	'	'	'
Assets:	'	'	'	'
Segment assets	714.8	721.3	'	'
Corporate, Non-Segment [Member]	'	'	'	'
Assets:	'	'	'	'
Cash & cash equivalents	30	4.8	'	'
Income tax receivable	9	1.6	'	'
Deferred taxes	13.3	35.5	'	'
Deferred financing costs	7.2	7.2	'	'
Property, plant and equipment, net	3.8	3.5	'	'
Deferred charges	2.6	2.6	'	'
Other	4.2	3.5	'	'
Carbon Materials and Chemicals [Member] | Operating Segments [Member]	'	'	'	'
Assets:	'	'	'	'
Segment assets	535.5	516.3	'	'
Goodwill:	'	'	'	'
Goodwill	68	70.2	'	'
Railroad and Utility Products and Services [Member] | Operating Segments [Member]	'	'	'	'
Assets:	'	'	'	'
Segment assets	179.3	205	'	'
Goodwill:	'	'	'	'
Goodwill	$4.70	$5.40	'	'

Segment_Information_Schedule_o

Segment Information - Schedule of Revenues and Long-Lived Assets by Geographic Area (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue from external customers	$341.80	$395.20	$370.90	$370.40	$374.90	$387.90	$411.30	$380.90	$1,478.30	$1,555	$1,466.20
Long-lived assets	302.5	'	'	'	271.6	'	'	'	302.5	271.6	256
United States [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue from external customers	'	'	'	'	'	'	'	'	782.5	827.6	787.5
Long-lived assets	169.1	'	'	'	162.9	'	'	'	169.1	162.9	161.6
Australia [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue from external customers	'	'	'	'	'	'	'	'	348.3	318.9	276.6
Long-lived assets	100.6	'	'	'	72.4	'	'	'	100.6	72.4	58.7
Europe [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue from external customers	'	'	'	'	'	'	'	'	225.1	247.8	248
Long-lived assets	32.8	'	'	'	36.3	'	'	'	32.8	36.3	35.7
Other Countries [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue from external customers	'	'	'	'	'	'	'	'	122.4	160.7	154.1
Long-lived assets	$0	'	'	'	$0	'	'	'	$0	$0	$0

Segment_Information_Schedule_o1

Segment Information - Schedule of Segment Revenues for Significant Product Lines (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	$341.80	$395.20	$370.90	$370.40	$374.90	$387.90	$411.30	$380.90	$1,478.30	$1,555	$1,466.20
Carbon Materials and Chemicals [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	906.1	999.7	943.1
Carbon Materials and Chemicals [Member] | Carbon Pitch [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	384.7	442.4	431.1
Carbon Materials and Chemicals [Member] | Creosote and Carbon Black Feedstock [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	228.2	233.8	162
Carbon Materials and Chemicals [Member] | Phthalic Anhydride [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	98.6	120	112.4
Carbon Materials and Chemicals [Member] | Naphthalene [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	64.5	60.3	72.3
Carbon Materials and Chemicals [Member] | Other Products [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	130.1	143.2	165.3
Railroad and Utility Products and Services [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	572.2	555.3	523.1
Railroad and Utility Products and Services [Member] | Other Products [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	35.9	30.3	36.6
Railroad and Utility Products and Services [Member] | Railroad Crossties [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	331.1	341.1	324.9
Railroad and Utility Products and Services [Member] | Utility Poles [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	119.3	101.3	84.2
Railroad and Utility Products and Services [Member] | Creosote [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	61.4	57	52.7
Railroad and Utility Products and Services [Member] | Rail Joint Bars [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	$24.50	$25.60	$24.70

Inventories_Components_of_Inve

Inventories - Components of Inventories (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Inventory Disclosure [Abstract]	'	'
Raw materials	$105.40	$118.20
Work in process	19.2	20
Finished goods	94.8	109.7
Inventories, gross	219.4	247.9
Less revaluation to LIFO	50.6	52.1
Net	$168.80	$195.80

Inventories_Additional_Informa

Inventories - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2011
Inventory Disclosure [Abstract]	'	'
Increase in operating profit due to LIFO liquidations	$0.20	$0.30

Equity_Investments_Additional_

Equity Investments - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]	'
Ownership percentage	30.00%
Dividends Paid	$0
KSA Limited Partnership [Member]	'
Schedule of Equity Method Investments [Line Items]	'
Ownership percentage	50.00%
Tangshan Koppers Kailuan Carbon Chemical Company Limited [Member]	'
Schedule of Equity Method Investments [Line Items]	'
Ownership percentage	30.00%

Equity_Investments_Equity_Earn

Equity Investments - Equity Earnings (Losses) and Dividends Received (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Equity Method Investments And Joint Ventures [Abstract]	'	'	'
Equity income	$0.80	$0.80	$0.20

Property_Plant_and_Equipment_P

Property, Plant and Equipment - Property, Plant and Equipment (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	$647.80	$581.80
Less accumulated depreciation	450.8	420.7
Net	197	161.1
Land [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	9.1	7
Buildings [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	30.6	31.7
Machinery and Equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property, plant and equipment, gross	$608.10	$543.10

Property_Plant_and_Equipment_A

Property, Plant and Equipment - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Oct. 31, 2013	Feb. 29, 2012	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	Battery	T
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'
Depreciation including impairment charges	'	'	'	$38.30	$25.20	$46
Impairment charges	'	'	11.9	11.9	0.6	0
Impairment charges, discontinued operation	'	'	'	'	'	20.2
Assets Impairment charges due to change in production operation	'	'	'	0.7	'	'
Plant subject to impairment	'	'	197	197	161.1	'
Number of coke batteries to be closed	2	'	'	'	'	'
Supply of export commitments	'	'	30.00%	30.00%	'	'
Liquid carbon pitch leaked from storage tank	'	400	'	'	'	'
Cost associated with leak	'	'	'	'	2.5	'
Estimated insurance recoveries, net	'	'	1.2	1.2	'	'
Restatement Adjustment [Member] | Machinery and Equipment [Member]	'	'	'	'	'	'
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'
Increase decrease in accumulated depreciation for property plant and equipment	'	'	'	'	78.2	'
Increase decrease in gross carrying amount for property plant and equipment	'	'	'	'	78.2	'
Koppers Carbon and Chemical Company Limited [Member]	'	'	'	'	'	'
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'
Percentage of operations in Tangshan, China of owned subsidiary	60.00%	'	'	'	'	'
Profit after deduction of profit attributable to non-controlling interests	'	'	'	3.3	'	'
Book value of fixed assets	'	'	8.1	8.1	'	'
Carbon Materials and Chemicals [Member]	'	'	'	'	'	'
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'
Impairment charges	'	'	'	11.9	'	'
Netherlands [Member]	'	'	'	'	'	'
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'
Plant subject to impairment	'	'	1.8	1.8	'	'
Netherlands [Member] | Carbon Materials and Chemicals [Member]	'	'	'	'	'	'
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'
Impairment charges	'	'	'	6.9	'	'
China [Member]	'	'	'	'	'	'
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'
Percentage of operations in Tangshan, China of owned subsidiary	'	'	'	60.00%	'	'
China [Member] | Carbon Materials and Chemicals [Member]	'	'	'	'	'	'
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'
Impairment charges	'	'	'	4	'	'
Assets impairment charges net of non controlling interest	'	'	'	2.4	'	'
United States [Member] | Carbon Materials and Chemicals [Member]	'	'	'	'	'	'
Property Plant And Equipment Disclosure [Line Items]	'	'	'	'	'	'
Impairment charges	'	'	'	$0.70	'	'

Goodwill_and_Other_Identifiabl2

Goodwill and Other Identifiable Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Acquired Finite-Lived Intangible Assets [Line Items]	'	'
Balance beginning	$75.60	$72.10
Acquisitions	'	2.6
Currency translation	-2.9	0.9
Balance ending	72.7	75.6
Carbon Materials and Chemicals [Member]	'	'
Acquired Finite-Lived Intangible Assets [Line Items]	'	'
Balance beginning	70.2	69.4
Acquisitions	'	0
Currency translation	-2.2	0.8
Balance ending	68	70.2
Railroad and Utility Products and Services [Member]	'	'
Acquired Finite-Lived Intangible Assets [Line Items]	'	'
Balance beginning	5.4	2.7
Acquisitions	'	2.6
Currency translation	-0.7	0.1
Balance ending	$4.70	$5.40

Goodwill_and_Other_Identifiabl3

Goodwill and Other Identifiable Intangible Assets - Schedule of Identifiable Intangible Assets (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Acquired Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	$25.10	$26.20
Accumulated Amortization	12.9	10.9
Net	12.2	15.3
Customer Contracts [Member]	'	'
Acquired Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	19.8	20.9
Accumulated Amortization	9.7	8.1
Net	10.1	12.8
Supply Contracts [Member]	'	'
Acquired Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	2.9	2.8
Accumulated Amortization	1.1	0.8
Net	1.8	2
Non-Compete Agreements [Member]	'	'
Acquired Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	1.6	1.7
Accumulated Amortization	1.3	1.2
Net	0.3	0.5
Favorable Lease Agreements [Member]	'	'
Acquired Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	0.8	0.8
Accumulated Amortization	0.8	0.8
Net	$0	$0

Goodwill_and_Other_Identifiabl4

Goodwill and Other Identifiable Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended			12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2012
				Foreign Currency Translation [Member]	Customer Contracts [Member]	Customer Contracts [Member]	Supply Contracts [Member]	Non-Compete Agreements [Member]	Non-Compete Agreements [Member]	Favorable Lease Agreements [Member]
					Minimum [Member]	Maximum [Member]		Minimum [Member]	Maximum [Member]
Goodwill And Other Intangible Assets [Line Items]	'	'	'	'	'	'	'	'	'	'
Carrying value of identifiable intangible assets decreased	'	'	'	$1.10	'	'	'	'	'	'
Estimated useful lives, in years	'	'	'	'	'10 years	'15 years	'10 years	'3 years	'12 years	'3 years
Amortization expense	$2.10	$1.90	$1.50	'	'	'	'	'	'	'
Identifiable intangible assets amortization period	'10 years 1 month 6 days	'	'	'	'	'	'	'	'	'

Goodwill_and_Other_Identifiabl5

Goodwill and Other Identifiable Intangible Assets - Schedule of Future Amortization Expense (Detail) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Goodwill And Intangible Assets Disclosure [Abstract]	'
2014	$1.80
2015	1.8
2016	1.3
2017	1.1
2018	$1.10

Debt_Schedule_of_LongTerm_Debt

Debt - Schedule of Long-Term Debt Instruments (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Proforma Debt Instrument [Line Items]	'	'
Senior Notes	$296.50	$296.10
Total debt	303.1	296.1
Less short-term debt and current maturities of long-term debt	0	0
Long-term debt (excluding current portion)	303.1	296.1
Revolving Credit Facility [Member]	'	'
Proforma Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	0.00%	'
Debt, Maturity	'2018	'
Revolving credit facility	0	0
Construction Loans [Member]	'	'
Proforma Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	6.24%	'
Debt, Maturity	'2018	'
Construction loans	6.6	0
Senior Notes [Member]	'	'
Proforma Debt Instrument [Line Items]	'	'
Debt, Weighted Average Interest Rate	7.88%	'
Debt, Maturity	'2019	'
Long-term debt (excluding current portion)	$303.10	$296.10

Debt_Additional_Information_De

Debt - Additional Information (Detail)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 01, 2009

Dec. 31, 2013

Nov. 18, 2013

Dec. 31, 2013

Dec. 31, 2012

Nov. 18, 2013

Nov. 18, 2013

Nov. 18, 2013

Nov. 18, 2013

In Millions, unless otherwise specified

USD ($)

USD ($)

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Senior Notes [Member]

Senior Notes [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

Construction Loans [Member]

USD ($)

USD ($)

USD ($)

USD ($)

Installment

USD ($)

USD ($)

Third Party Debt [Member]

Lender [Member]

Koppers Carbon and Chemical Company Limited [Member]

Koppers Carbon and Chemical Company Limited [Member]

CNY

Committed Credit Facility [Member]

USD ($)

CNY

CNY

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of credit facility, borrowing capacity

'

'

$350

'

'

'

'

'

'

'

'

'

'

'

Line of credit facility, commitment fees

'

'

1

1

1.1

'

'

'

'

'

'

'

'

'

Debt instrument, unused borrowing capacity

'

'

331

'

'

'

'

'

'

'

'

'

'

'

Letters of credit, amount outstanding

'

'

19

'

'

'

'

'

'

'

'

'

'

'

Percentage of owned subsidiary

'

'

'

'

'

'

'

'

'

'

'

'

75.00%

75.00%

Construction loan facility borrowing capacity

'

'

'

'

'

'

'

'

6.6

0

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

'

'

0.00%

'

'

'

7.88%

'

6.24%

'

'

'

'

'

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 DecemberB 1 and JuneB 1 each year

'

'

'

'

'

'

'

Accumulated amortization

5.9

4.6

'

'

'

'

'

'

'

'

'

'

'

'

Unamortized deferred financing costs

$7.20

$7.20

'

'

'

'

'

'

'

'

'

'

'

'

Debt_Schedule_of_Debt_Maturiti

Debt - Schedule of Debt Maturities (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Debt Disclosure [Abstract]	'	'
2014	$0	'
2015	0	'
2016	1	'
2017	2.3	'
2018	3.3	'
Thereafter	300	'
Total maturities	306.6	'
Future accretion on Senior Notes	-3.5	'
Total debt	$303.10	$296.10

Leases_Future_Minimum_Commitme

Leases - Future Minimum Commitments for Operating Leases (Detail) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Leases [Abstract]	'
2014	$37
2015	21.2
2016	16.4
2017	14
2018	12.3
Thereafter	30
Total	$130.90

Leases_Additional_Information_

Leases - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Leases [Abstract]	'	'	'
Operating lease expense	$39.40	$44.30	$43.80

Pensions_and_Postretirement_Be2

Pensions and Post-retirement Benefit Plans - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	Plans
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Number of domestic non qualified defined benefit plan	3	'	'
Defined contribution plans expense	$5.30	$4.70	$4.80
Multi-employer contribution plan expense	0.4	0.4	0.7
Amortization of prior service cost	-0.2	'	'
Amortization of net loss	3.8	'	'
Accumulated benefit obligation pension plans	230.6	235.9	'
Operating expense	2.3	5.2	5.6
Growth seeking assets [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Target allocation investment strategy, minimum	30.00%	'	'
Target allocation investment strategy, maximum	40.00%	'	'
Income generating assets [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Target allocation investment strategy, minimum	60.00%	'	'
Target allocation investment strategy, maximum	70.00%	'	'
Maximum [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Initial health care cost trend rate	7.35%	'	'
Minimum [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Initial health care cost trend rate	4.50%	'	'
Pension Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Expected contributions by the employer	22.8	'	'
Other Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Expected contributions by the employer	$0.80	'	'
Initial health care cost trend rate	7.15%	7.35%	'

Pensions_and_Postretirement_Be3

Pensions and Post-retirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	$3.40	$3.50	$3.30
Interest cost	10.7	10.7	11.1
Expected return on plan assets	-12.5	-10.7	-11
Amortization of prior service cost	0.1	0.1	0.1
Amortization of net loss	7.6	8.1	6.3
Amortization of transition asset	0	-0.3	-0.3
Settlements and curtailments	0.1	0.3	0.2
Net periodic benefit cost	9.4	11.7	9.7
Other Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	0.1	0.1	0.2
Interest cost	0.5	0.5	0.6
Expected return on plan assets	0	0	0
Amortization of prior service cost	0	0	-0.1
Amortization of net loss	-0.1	0	0
Amortization of transition asset	0	0	0
Settlements and curtailments	0	0	0
Net periodic benefit cost	$0.50	$0.60	$0.70

Pensions_and_Postretirement_Be4

Pensions and Post-retirement Benefit Plans - Schedule of Change in Funded Status of Pension and Post-Retirement Plans (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Fair value of plan assets at end of year	$205.70	$175.60	'
Noncurrent liabilities	41.6	89.9	'
Pension Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Benefit obligation at beginning of year	255.2	239.5	'
Service cost	3.4	3.5	3.3
Interest cost	10.7	10.7	11.1
Plan participants' contributions	0.2	0.2	'
Actuarial (gains) losses	-18.6	10.3	'
Plan amendments	-1.5	0	'
Settlements	-0.9	-1.4	'
Currency translation	0.2	2.4	'
Benefits paid	-10.9	-10	'
Benefit obligation at end of year	237.8	255.2	239.5
Fair value of plan assets at beginning of year	175.6	146.6	'
Actual return on plan assets	19.2	15.7	'
Employer contribution	22.5	22.4	'
Plan participants' contributions	0.2	0.2	'
Settlements	-0.9	-1.4	'
Currency translation	0	2.1	'
Benefits paid	-10.9	-10	'
Fair value of plan assets at end of year	205.7	175.6	146.6
Funded status of the plan	-32.1	-79.6	'
Noncurrent assets	0.6	0.2	'
Current liabilities	0.7	0.4	'
Noncurrent liabilities	32	79.4	'
Benefit obligation	231.9	247.5	'
Fair value of plan assets	199.2	167.6	'
Accumulated benefit obligation	225	229	'
Fair value of plan assets	199.2	167.6	'
Other Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Benefit obligation at beginning of year	11.2	12.5	'
Service cost	0.1	0.1	0.2
Interest cost	0.5	0.5	0.6
Plan participants' contributions	0	0	'
Actuarial (gains) losses	-1.3	-1.8	'
Plan amendments	0	0	'
Settlements	0	0	'
Currency translation	0	0	'
Benefits paid	-0.1	-0.1	'
Benefit obligation at end of year	10.4	11.2	12.5
Fair value of plan assets at beginning of year	0	0	'
Actual return on plan assets	0	0	'
Employer contribution	0.1	0.1	'
Plan participants' contributions	0	0	'
Settlements	0	0	'
Currency translation	0	0	'
Benefits paid	-0.1	-0.1	'
Fair value of plan assets at end of year	0	0	0
Funded status of the plan	-10.4	-11.2	'
Noncurrent assets	0	0	'
Current liabilities	0.8	0.7	'
Noncurrent liabilities	$9.60	$10.50	'

Pensions_and_Postretirement_Be5

Pensions and Post-retirement Benefit Plans - Schedule of Projected Benefit Payments (Detail) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Pension Benefits [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	$11.20
2015	11.7
2016	12.6
2017	13.5
2018	14.5
2019 - 2023	74.5
Other Benefits [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	0.8
2015	0.8
2016	0.8
2017	0.9
2018	0.9
2019 - 2023	$4

Pensions_and_Postretirement_Be6

Pensions and Post-retirement Benefit Plans - Schedule of Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Discount rate	5.06%	4.33%
Expected return on plan assets	7.04%	7.25%
Rate of compensation increase	3.13%	3.10%
Other Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Discount rate	5.25%	4.37%
Initial medical trend rate	7.15%	7.35%

Pensions_and_Postretirement_Be7

Pensions and Post-retirement Benefits Plan - Schedule of Weighted Average Asset Allocation for Company's Pension Plans (Detail)	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]	'	'
Total asset allocation	100.00%	100.00%
Equity Securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Total asset allocation	38.00%	61.00%
Debt Securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Total asset allocation	59.00%	35.00%
Other [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Total asset allocation	3.00%	4.00%

Pension_and_Postretirement_Ben

Pension and Post-retirement Benefit Plans - Schedule of Pension Plan Assets at Fair Value (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	$205.70	$175.60
U.S. equity securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	33.7	80
International equity securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	44.3	27.2
U.S. debt securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	89.5	36.4
International debt securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	32.3	24.5
Real estate and other investments [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	1.5	1.7
Cash & Cash Equivalents [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	4.4	5.8
Quoted prices in active markets for identical assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	50	0
Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. equity securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	17.8	0
Quoted prices in active markets for identical assets (Level 1) [Member] | International equity securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. debt securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	24.8	0
Quoted prices in active markets for identical assets (Level 1) [Member] | International debt securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	7.4	0
Quoted prices in active markets for identical assets (Level 1) [Member] | Real estate and other investments [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | Cash & Cash Equivalents [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	0	0
Significant observable inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	155.7	175.6
Significant observable inputs (Level 2) [Member] | U.S. equity securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	15.9	80
Significant observable inputs (Level 2) [Member] | International equity securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	44.3	27.2
Significant observable inputs (Level 2) [Member] | U.S. debt securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	64.7	36.4
Significant observable inputs (Level 2) [Member] | International debt securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	24.9	24.5
Significant observable inputs (Level 2) [Member] | Real estate and other investments [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	1.5	1.7
Significant observable inputs (Level 2) [Member] | Cash & Cash Equivalents [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	4.4	5.8
Significant unobservable inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | U.S. equity securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | International equity securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | U.S. debt securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | International debt securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | Real estate and other investments [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	0	0
Significant unobservable inputs (Level 3) [Member] | Cash & Cash Equivalents [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of pension plan assets	$0	$0

Pensions_and_Postretirement_Be8

Pensions and Post-retirement Benefits Plans - Schedule of Health Care Cost Trend Rates (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Postemployment Benefits [Abstract]	'
Postretirement benefit expense one-percentage increase	$0
Postretirement benefit liability one-percentage increase	0.2
Postretirement benefit expense one-percentage decrease	0
Postretirement benefit liability one-percentage decrease	($0.20)

Common_Stock_and_Senior_Conver2

Common Stock and Senior Convertible Preferred Stock - Schedule of Changes in Senior Convertible Preferred Stock, Common Stock and Treasury Stock (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Senior Convertible Preferred Stock:	'	'	'
Balance at beginning and end of year	0	0	0
Common Stock:	'	'	'
Balance at beginning of year	21,585,000	21,309,000	21,278,000
Issued for employee stock plans	137,000	276,000	31,000
Balance at end of year	21,722,000	21,585,000	21,309,000
Treasury Stock:	'	'	'
Balance at beginning of year	-951,026	-706,000	-700,000
Shares repurchased	-439,000	-245,000	-6,000
Balance at end of year	-1,390,494	-951,026	-706,000

Fair_Value_of_Financial_Instru2

Fair Value of Financial Instruments - Schedule of Company's Financial Instruments (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Fair Value [Member]	'	'
Financial assets:	'	'
Cash and cash equivalents	$82.20	$66.70
Investments and other assets	1.4	1.4
Financial liabilities:	'	'
Long-term debt (including current portion)	331.2	331.1
Carrying Value [Member]	'	'
Financial assets:	'	'
Cash and cash equivalents	82.2	66.7
Investments and other assets	1.4	1.4
Financial liabilities:	'	'
Long-term debt (including current portion)	$303.10	$296.10

Commitments_and_Contingent_Lia2

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

1 Months Ended

12 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

Sep. 30, 2013

Jul. 31, 2013

Sep. 30, 2012

Jul. 31, 2012

Jul. 31, 2004

Dec. 31, 2013

Dec. 31, 2012

Mar. 30, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2011

Plaintiff

Plaintiff

site

Compensatory Damages [Member]

Punitive Damages [Member]

Pennsylvania [Member]

Arkansas [Member]

Tennessee [Member]

Australia [Member]

Australia [Member]

State

Cases

Cases

Cases

Cases

Cases

Cases

site

Cases

Commitments And Contingent Liabilities [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of states new claims filed

'

'

'

'

'

3

'

'

'

'

'

'

'

'

'

Number of plaintiffs

'

'

'

'

'

111

136

'

'

'

'

'

'

'

'

Number of cases

'

'

'

'

'

61

75

'

61

56

57

3

1

'

'

Compensatory damages

'

$3,100,000

$1,700,000

'

'

'

'

'

'

'

'

$50,000

$15,000,000

'

'

Plant operation resumption period

'

'

'

'21 days

'

'

'

'

'

'

'

'

'

'

'

Environmental legal indemnification expense

'

'

'

'

7,000,000

'

'

'

'

'

'

'

'

'

'

Number of sites listed on national priorities list

'

'

'

'

'

1

'

'

'

'

'

'

'

'

'

Environmental remediation costs paid by others, per year

'

'

'

'

'

15,000,000

'

'

'

'

'

'

'

'

'

Environmental Protection Agency

'

'

'

'

'

80

'

'

'

'

'

'

'

'

'

Possible remedial alternatives

'

'

'

'

'

'

'

10

'

'

'

'

'

'

'

Remedial alternatives

'

'

'

'

'

'

'

170,000,000

'

'

'

'

'

'

'

Remedial alternatives

'

'

'

'

'

'

'

1,800,000,000

'

'

'

'

'

'

'

Environmental contingencies reserve not provided by company

'

'

'

'

'

1,000,000

'

'

'

'

'

'

'

'

'

Environmental remediation expense

'

'

'

'

'

'

'

'

'

'

'

'

'

5,600,000

1,600,000

Amount contributable by third party

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7,500,000

Environmental remediation reserve

'

'

'

'

'

1,800,000

1,000,000

'

'

'

'

'

'

'

4,100,000

Net amount contributed by third party

'

'

'

'

'

'

'

'

'

'

'

'

'

2,700,000

'

Accrued liability for environmental matters, current

'

'

'

'

'

8,200,000

8,500,000

'

'

'

'

'

'

'

'

Reversal of reserve includes sale to unaffiliated third party

$1,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Commitments_and_Contingent_Lia3

Commitments and Contingent Liabilities - Changes in Accrued Liability for Environmental Matters (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Commitments And Contingencies Disclosure [Abstract]	'	'
Balance at beginning of year	$14.10	$17.70
Expense	1.8	1
Reversal of reserves	-1.2	-0.4
Cash expenditures	-0.9	-4.6
Currency translation	-1.9	0.4
Balance at end of year	$11.90	$14.10

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Related Party Transactions [Abstract]	'	'
Loan to related party	$9.50	$9.50
Ownership percentage	30.00%	'
Loan repayable date	'November 2014	'
Loan repayment extended period	'11 months	'

Subsequent_Event_Additional_In

Subsequent Event - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
			Scenario, Forecast [Member]
Subsequent Event [Line Items]	'	'	'
Intangible asset impairment charge	$7	'	'
Restructuring charges	'	$0.50	$25

Selected_Quarterly_Financial_D2

Selected Quarterly Financial Data - Schedule of Selected Quarterly Financial Data (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of operations data:	'	'	'	'	'	'	'	'	'	'	'
Net sales	$341.80	$395.20	$370.90	$370.40	$374.90	$387.90	$411.30	$380.90	$1,478.30	$1,555	$1,466.20
Operating profit	7.8	39.1	28.5	24.9	25.9	30.8	40.7	29.2	100.3	126.6	122.7
Income from continuing operations	-5.6	19.6	14.8	11.4	14.2	16.2	21.1	15.8	40.2	67.3	57.5
Net income (loss)	-5.6	19.5	14.7	11.5	14.2	16.2	20.9	15.9	40.1	67.2	37.6
Net income (loss) attributable to Koppers	($4.10)	$19.10	$14.40	$11	$13.60	$16	$20.40	$15.60	$40.40	$65.60	$36.90
Basic -	'	'	'	'	'	'	'	'	'	'	'
Continuing operations	($0.20)	$0.93	$0.70	$0.53	$0.66	$0.77	$1	$0.74	$1.96	$3.18	$2.75
Discontinued operations	$0	$0	($0.01)	$0	$0	$0	($0.01)	$0.01	$0	($0.01)	($0.96)
Earnings per basic common share	($0.20)	$0.93	$0.69	$0.53	$0.66	$0.77	$0.99	$0.75	$1.96	$3.17	$1.79
Diluted -	'	'	'	'	'	'	'	'	'	'	'
Continuing operations	($0.20)	$0.92	$0.70	$0.53	$0.65	$0.77	$0.99	$0.74	$1.94	$3.14	$2.72
Discontinued operations	$0	$0	($0.01)	$0	$0	$0	($0.01)	$0.01	$0	($0.01)	($0.95)
Earnings per diluted common share	($0.20)	$0.92	$0.69	$0.53	$0.65	$0.77	$0.98	$0.75	$1.94	$3.13	$1.77
Dividends declared per common share	$0.25	$0.25	$0.25	$0.25	$0.24	$0.24	$0.24	$0.24	$1	$0.96	$0.88
Maximum [Member]	'	'	'	'	'	'	'	'	'	'	'
Price range of common stock:	'	'	'	'	'	'	'	'	'	'	'
Price range of common stock	$49.99	$42.09	$46.48	$45.72	$38.83	$37.82	$40.37	$40.61	$49.99	$40.61	'
Minimum [Member]	'	'	'	'	'	'	'	'	'	'	'
Price range of common stock:	'	'	'	'	'	'	'	'	'	'	'
Price range of common stock	$41.61	$34.69	$37.45	$38.70	$30.99	$29.30	$31.17	$32.15	$34.69	$29.30	'

Selected_Quarterly_Financial_D3

Selected Quarterly Financial Data - Schedule of Selected Quarterly Financial Data (Parenthetical) (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]	'	'	'	'
Fixed asset impairment charges	$11.90	$11.90	$0.60	$0

Subsidiary_Guarantor_Informati4

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 01, 2009	Dec. 31, 2013	Dec. 31, 2013
	Payment Guarantee by Subsidiaries for Senior Notes [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]	Payment Guarantee by Subsidiaries for Senior Notes [Member]	Senior Notes [Member]	Revolving Credit Facility [Member]	Revolving Credit Facility [Member]
						Payment Guarantee by Subsidiaries for Senior Notes [Member]
Debt Instrument [Line Items]	'	'	'	'	'	'
Principal value of Senior Notes	'	'	'	$300	'	'
Percent-owned material domestic subsidiaries	'	'	'	100.00%	'	'
Revolving credit facility	350	'	'	'	350	'
Restricted net assets	'	'	'	'	'	147
Cash dividends paid	$38.50	$27.60	$2.50	'	'	'

Subsidiary_Guarantor_Informati5

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Statement of Comprehensive Income (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	$341.80	$395.20	$370.90	$370.40	$374.90	$387.90	$411.30	$380.90	$1,478.30	$1,555	$1,466.20
Selling, general and administrative	'	'	'	'	'	'	'	'	71.7	75.6	74.3
Operating profit (loss)	7.8	39.1	28.5	24.9	25.9	30.8	40.7	29.2	100.3	126.6	122.7
Other income (expense)	'	'	'	'	'	'	'	'	3.5	1.9	0.7
Equity income of subsidiaries	'	'	'	'	'	'	'	'	0.8	0.8	0.2
Income taxes	'	'	'	'	'	'	'	'	36.8	33.3	38.7
Income from continuing operations	-5.6	19.6	14.8	11.4	14.2	16.2	21.1	15.8	40.2	67.3	57.5
Discontinued operations	'	'	'	'	'	'	'	'	-0.1	-0.1	-19.9
Noncontrolling interests	'	'	'	'	'	'	'	'	-0.3	1.6	0.7
Net income attributable to Koppers	-4.1	19.1	14.4	11	13.6	16	20.4	15.6	40.4	65.6	36.9
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	52.3	73.7	18.9
Senior Notes [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	1,478.30	1,555	1,466.20
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	1,306.30	1,352.80	1,269.20
Selling, general and administrative	'	'	'	'	'	'	'	'	71.7	75.6	74.3
Operating profit (loss)	'	'	'	'	'	'	'	'	100.3	126.6	122.7
Other income (expense)	'	'	'	'	'	'	'	'	3.5	1.9	0.7
Equity income of subsidiaries	'	'	'	'	'	'	'	'	0	0	0
Interest expense	'	'	'	'	'	'	'	'	26.8	27.9	27.2
Income taxes	'	'	'	'	'	'	'	'	36.8	33.3	38.7
Income from continuing operations	'	'	'	'	'	'	'	'	40.2	67.3	57.5
Discontinued operations	'	'	'	'	'	'	'	'	-0.1	-0.1	-19.9
Noncontrolling interests	'	'	'	'	'	'	'	'	-0.3	1.6	0.7
Net income attributable to Koppers	'	'	'	'	'	'	'	'	40.4	65.6	36.9
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	52.3	73.7	18.9
Parent [Member] | Senior Notes [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	0	0	0
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	0	0	0
Selling, general and administrative	'	'	'	'	'	'	'	'	1.9	1.6	1.2
Operating profit (loss)	'	'	'	'	'	'	'	'	-1.9	-1.6	-1.2
Other income (expense)	'	'	'	'	'	'	'	'	0	0	0
Equity income of subsidiaries	'	'	'	'	'	'	'	'	41.7	66.6	37.7
Interest expense	'	'	'	'	'	'	'	'	0	0	0
Income taxes	'	'	'	'	'	'	'	'	-0.6	-0.6	-0.4
Income from continuing operations	'	'	'	'	'	'	'	'	40.4	65.6	36.9
Discontinued operations	'	'	'	'	'	'	'	'	0	0	0
Noncontrolling interests	'	'	'	'	'	'	'	'	0	0	0
Net income attributable to Koppers	'	'	'	'	'	'	'	'	40.4	65.6	36.9
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	52.3	73.7	18.9
Koppers Inc. [Member] | Senior Notes [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	843.7	893.2	854.1
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	745.4	786.6	762.9
Selling, general and administrative	'	'	'	'	'	'	'	'	41.5	45.1	41.6
Operating profit (loss)	'	'	'	'	'	'	'	'	56.8	61.5	49.6
Other income (expense)	'	'	'	'	'	'	'	'	1.3	0.4	0.3
Equity income of subsidiaries	'	'	'	'	'	'	'	'	17.5	40.8	22.9
Interest expense	'	'	'	'	'	'	'	'	26.7	27.4	27.4
Income taxes	'	'	'	'	'	'	'	'	7.3	8.7	7.7
Income from continuing operations	'	'	'	'	'	'	'	'	41.6	66.6	37.7
Discontinued operations	'	'	'	'	'	'	'	'	0.1	0	0
Noncontrolling interests	'	'	'	'	'	'	'	'	0	0	0
Net income attributable to Koppers	'	'	'	'	'	'	'	'	41.7	66.6	37.7
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	53.5	74.8	19.7
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	61.8	97.5	72.6
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	43.5	78	55
Selling, general and administrative	'	'	'	'	'	'	'	'	0.7	2.1	1.8
Operating profit (loss)	'	'	'	'	'	'	'	'	17.6	17.4	15.8
Other income (expense)	'	'	'	'	'	'	'	'	4.2	6.1	5.5
Equity income of subsidiaries	'	'	'	'	'	'	'	'	11.4	28.8	1.3
Interest expense	'	'	'	'	'	'	'	'	0	0	0.1
Income taxes	'	'	'	'	'	'	'	'	16.4	12.5	0.8
Income from continuing operations	'	'	'	'	'	'	'	'	16.8	39.8	21.7
Discontinued operations	'	'	'	'	'	'	'	'	0	0	0
Noncontrolling interests	'	'	'	'	'	'	'	'	0	0	0
Net income attributable to Koppers	'	'	'	'	'	'	'	'	16.8	39.8	21.7
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	8.4	44	17.3
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	622.2	638.4	585.2
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	566.9	562	497
Selling, general and administrative	'	'	'	'	'	'	'	'	27.6	26.8	29.7
Operating profit (loss)	'	'	'	'	'	'	'	'	27.7	49.6	58.5
Other income (expense)	'	'	'	'	'	'	'	'	2.1	0.6	0.4
Equity income of subsidiaries	'	'	'	'	'	'	'	'	0	0.1	0
Interest expense	'	'	'	'	'	'	'	'	4.2	5.8	5.2
Income taxes	'	'	'	'	'	'	'	'	13.7	12.7	30.6
Income from continuing operations	'	'	'	'	'	'	'	'	11.9	31.8	23.1
Discontinued operations	'	'	'	'	'	'	'	'	-0.2	-0.1	-19.9
Noncontrolling interests	'	'	'	'	'	'	'	'	-0.3	1.6	0.7
Net income attributable to Koppers	'	'	'	'	'	'	'	'	12	30.1	2.5
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	13.8	32.4	-1.4
Consolidating Adjustments [Member] | Senior Notes [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	-49.4	-74.1	-45.7
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	-49.5	-73.8	-45.7
Selling, general and administrative	'	'	'	'	'	'	'	'	0	0	0
Operating profit (loss)	'	'	'	'	'	'	'	'	0.1	-0.3	0
Other income (expense)	'	'	'	'	'	'	'	'	-4.1	-5.2	-5.5
Equity income of subsidiaries	'	'	'	'	'	'	'	'	-70.6	-136.3	-61.9
Interest expense	'	'	'	'	'	'	'	'	-4.1	-5.3	-5.5
Income taxes	'	'	'	'	'	'	'	'	0	0	0
Income from continuing operations	'	'	'	'	'	'	'	'	-70.5	-136.5	-61.9
Discontinued operations	'	'	'	'	'	'	'	'	0	0	0
Noncontrolling interests	'	'	'	'	'	'	'	'	0	0	0
Net income attributable to Koppers	'	'	'	'	'	'	'	'	-70.5	-136.5	-61.9
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	($75.70)	($151.20)	($35.60)

Subsidiary_Guarantor_Informati6

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Balance Sheet (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Millions, unless otherwise specified
ASSETS	'	'	'	'
Cash and cash equivalents	$82.20	$66.70	$54.10	$35.30
Receivables, net	157.9	162.7	'	'
Inventories, net	168.8	195.8	'	'
Deferred tax assets	10	15.1	'	'
Other current assets	35.7	29.8	'	'
Total current assets	473.1	481.2	'	'
Equity investments	6.6	5.8	'	'
Property, plant and equipment, net	197	161.1	'	'
Goodwill	72.7	75.6	72.1	'
Deferred tax assets	9.3	27.2	'	'
Other noncurrent assets	26.2	29.1	'	'
Total assets	784.9	780	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	107.6	103.5	'	'
Accrued liabilities	82.4	72.1	'	'
Total current liabilities	195.1	181.2	'	'
Long-term debt	303.1	296.1	'	'
Total liabilities	595.1	611.9	'	'
Koppers shareholders' equity	169.8	150.6	'	'
Noncontrolling interests	20	17.5	'	'
Total liabilities and equity	784.9	780	'	'
Senior Notes [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	82.2	66.7	54.1	35.3
Receivables, net	166.9	164.3	'	'
Affiliated receivables	0	0	'	'
Inventories, net	168.8	195.8	'	'
Deferred tax assets	10	15.1	'	'
Other current assets	45.2	39.3	'	'
Total current assets	473.1	481.2	'	'
Equity investments	6.6	5.8	'	'
Property, plant and equipment, net	197	161.1	'	'
Goodwill	72.7	75.6	'	'
Deferred tax assets	9.3	27.2	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	26.2	29.1	'	'
Total assets	784.9	780	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	107.6	103.5	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	87.5	77.7	'	'
Total current liabilities	195.1	181.2	'	'
Long-term debt	303.1	296.1	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	96.9	134.6	'	'
Total liabilities	595.1	611.9	'	'
Koppers shareholders' equity	169.8	150.6	'	'
Noncontrolling interests	20	17.5	'	'
Total liabilities and equity	784.9	780	'	'
Parent [Member] | Senior Notes [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	0.2	0.7	'	'
Inventories, net	0	0	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	0.2	0.7	'	'
Equity investments	174.7	154.9	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	0	0	'	'
Total assets	174.9	155.6	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0	0.1	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	5.1	4.9	'	'
Total current liabilities	5.1	5	'	'
Long-term debt	0	0	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	5.1	5	'	'
Koppers shareholders' equity	169.8	150.6	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	174.9	155.6	'	'
Koppers Inc. [Member] | Senior Notes [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	29.9	4.8	0	8.4
Receivables, net	75.6	80.2	'	'
Affiliated receivables	1.1	0	'	'
Inventories, net	86.1	102.2	'	'
Deferred tax assets	7.9	9.4	'	'
Other current assets	7.3	6.4	'	'
Total current assets	207.9	203	'	'
Equity investments	333.5	648.3	'	'
Property, plant and equipment, net	112.2	105.7	'	'
Goodwill	39.8	39.8	'	'
Deferred tax assets	2.4	14.9	'	'
Affiliated loan receivables	8.5	7.7	'	'
Other noncurrent assets	15	15.7	'	'
Total assets	719.3	1,035.10	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	48.3	51.4	'	'
Affiliated payables	1.9	120.8	'	'
Accrued liabilities	27.8	15.9	'	'
Total current liabilities	78	188.1	'	'
Long-term debt	296.5	296.1	'	'
Affiliated debt	109.5	301	'	'
Other long-term liabilities	67.6	101.2	'	'
Total liabilities	551.6	886.4	'	'
Koppers shareholders' equity	167.7	148.7	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	719.3	1,035.10	'	'
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	0.1	0	0	0
Receivables, net	9.3	6.3	'	'
Affiliated receivables	3.9	119	'	'
Inventories, net	0	0	'	'
Deferred tax assets	1.5	5.5	'	'
Other current assets	0.6	2.8	'	'
Total current assets	15.4	133.6	'	'
Equity investments	182.9	183.8	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	-1.4	2.1	'	'
Affiliated loan receivables	123.8	326.3	'	'
Other noncurrent assets	0	0	'	'
Total assets	320.7	645.8	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	6.7	1.7	'	'
Affiliated payables	4	7.6	'	'
Accrued liabilities	0.5	12.2	'	'
Total current liabilities	11.2	21.5	'	'
Long-term debt	0	0	'	'
Affiliated debt	8.5	7.7	'	'
Other long-term liabilities	2.5	2.4	'	'
Total liabilities	22.2	31.6	'	'
Koppers shareholders' equity	298.5	614.2	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	320.7	645.8	'	'
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	52.2	61.9	54.1	26.9
Receivables, net	82	77.8	'	'
Affiliated receivables	2.3	9	'	'
Inventories, net	82.9	93.9	'	'
Deferred tax assets	0.6	0.2	'	'
Other current assets	37.3	30.1	'	'
Total current assets	257.3	272.9	'	'
Equity investments	4.6	3.8	'	'
Property, plant and equipment, net	84.8	55.4	'	'
Goodwill	32.9	35.8	'	'
Deferred tax assets	8.3	10.2	'	'
Affiliated loan receivables	40.9	39.3	'	'
Other noncurrent assets	11.2	13.4	'	'
Total assets	440	430.8	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	52.6	50.3	'	'
Affiliated payables	8.6	6.4	'	'
Accrued liabilities	54.1	44.7	'	'
Total current liabilities	115.3	101.4	'	'
Long-term debt	6.6	0	'	'
Affiliated debt	55.2	64.6	'	'
Other long-term liabilities	26.8	31	'	'
Total liabilities	203.9	197	'	'
Koppers shareholders' equity	216.1	216.3	'	'
Noncontrolling interests	20	17.5	'	'
Total liabilities and equity	440	430.8	'	'
Consolidating Adjustments [Member] | Senior Notes [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	-7.5	-128.7	'	'
Inventories, net	-0.2	-0.3	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	-7.7	-129	'	'
Equity investments	-689.1	-985	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	-173.2	-373.3	'	'
Other noncurrent assets	0	0	'	'
Total assets	-870	-1,487.30	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0	0	'	'
Affiliated payables	-14.5	-134.8	'	'
Accrued liabilities	0	0	'	'
Total current liabilities	-14.5	-134.8	'	'
Long-term debt	0	0	'	'
Affiliated debt	-173.2	-373.3	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	-187.7	-508.1	'	'
Koppers shareholders' equity	-682.3	-979.2	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	($870)	($1,487.30)	'	'

Subsidiary_Guarantor_Informati7

Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Statement of Cash Flows (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Subsidiary, Sale of Stock [Line Items]	'	'	'
Cash provided by (used in) operating activities	$117.60	$77.80	$76.90
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	-72.9	-28.9	-33.2
Loan repayment by related party	0	2.2	-11.7
Net cash proceeds (payments) from divestitures and asset sales	2.9	0.8	0.8
Net cash used in investing activities	-72.3	-39.9	-44.7
Cash provided by (used in) financing activities:	'	'	'
Deferred financing costs	-1.3	-0.1	-0.5
Dividends paid	-21.1	-19.5	-18.2
Net cash provided by (used in) financing activities	-30.3	-27.3	-13.3
Effect of exchange rates on cash	0.5	2	-0.1
Net increase (decrease) in cash and cash equivalents	15.5	12.6	18.8
Cash and cash equivalents at beginning of year	66.7	54.1	35.3
Cash and cash equivalents at end of period	82.2	66.7	54.1
Senior Notes [Member]	'	'	'
Subsidiary, Sale of Stock [Line Items]	'	'	'
Cash provided by (used in) operating activities	117.6	77.8	76.9
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	-75.2	-42.9	-33.8
Loan repayment by related party	'	2.2	-11.7
(Loans to) repayments from affiliates	0	0	0
Net cash proceeds (payments) from divestitures and asset sales	2.9	0.8	0.8
Net cash used in investing activities	-72.3	-39.9	-44.7
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	6.6	-6.4	5.4
Borrowings (repayments) of affiliated long-term debt	0	0	0
Deferred financing costs	-1.3	-0.1	-0.5
Dividends paid	-21.1	-19.5	-18.2
Stock issued and repurchased	-17.3	-6.6	'
Other financing receipts	2.8	5.3	'
Net cash provided by (used in) financing activities	-30.3	-27.3	-13.3
Effect of exchange rates on cash	0.5	2	-0.1
Net increase (decrease) in cash and cash equivalents	15.5	12.6	18.8
Cash and cash equivalents at beginning of year	66.7	54.1	35.3
Cash and cash equivalents at end of period	82.2	66.7	54.1
Parent [Member] | Senior Notes [Member]	'	'	'
Subsidiary, Sale of Stock [Line Items]	'	'	'
Cash provided by (used in) operating activities	37.8	26.1	18.2
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	0	0	0
Loan repayment by related party	'	0	0
(Loans to) repayments from affiliates	0	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0	0
Net cash used in investing activities	0	0	0
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	0	0	0
Borrowings (repayments) of affiliated long-term debt	0	0	0
Deferred financing costs	0	0	0
Dividends paid	-20.5	-19.5	-18.2
Stock issued and repurchased	-17.3	-6.6	'
Other financing receipts	0	0	'
Net cash provided by (used in) financing activities	-37.8	-26.1	-18.2
Effect of exchange rates on cash	0	0	0
Net increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of year	0	0	0
Cash and cash equivalents at end of period	0	0	0
Koppers Inc. [Member] | Senior Notes [Member]	'	'	'
Subsidiary, Sale of Stock [Line Items]	'	'	'
Cash provided by (used in) operating activities	278.7	44.6	30.3
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	-23.3	-21.3	-24.5
Loan repayment by related party	'	0	0
(Loans to) repayments from affiliates	-0.8	0.3	1.2
Net cash proceeds (payments) from divestitures and asset sales	1.3	0.4	0.7
Net cash used in investing activities	-22.8	-20.6	-22.6
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	0	-6.4	6.3
Borrowings (repayments) of affiliated long-term debt	-191.5	13.3	-19.2
Deferred financing costs	-1.3	-0.1	-0.5
Dividends paid	-38.5	-27.6	-2.5
Stock issued and repurchased	0	0	'
Other financing receipts	0.5	1.6	'
Net cash provided by (used in) financing activities	-230.8	-19.2	-15.9
Effect of exchange rates on cash	0	0	0.1
Net increase (decrease) in cash and cash equivalents	25.1	4.8	-8.4
Cash and cash equivalents at beginning of year	4.8	0	8.4
Cash and cash equivalents at end of period	29.9	4.8	0
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'
Subsidiary, Sale of Stock [Line Items]	'	'	'
Cash provided by (used in) operating activities	130.1	8.7	-15.5
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	0	0	0
Loan repayment by related party	'	0	0
(Loans to) repayments from affiliates	193.2	-8.4	16.7
Net cash proceeds (payments) from divestitures and asset sales	0	0	0
Net cash used in investing activities	193.2	-8.4	16.7
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	0	0	0
Borrowings (repayments) of affiliated long-term debt	0.8	-0.3	-1.2
Deferred financing costs	0	0	0
Dividends paid	-324	0	0
Stock issued and repurchased	0	0	'
Other financing receipts	0	0	'
Net cash provided by (used in) financing activities	-323.2	-0.3	-1.2
Effect of exchange rates on cash	0	0	0
Net increase (decrease) in cash and cash equivalents	0.1	0	0
Cash and cash equivalents at beginning of year	0	0	0
Cash and cash equivalents at end of period	0.1	0	0
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]	'	'	'
Subsidiary, Sale of Stock [Line Items]	'	'	'
Cash provided by (used in) operating activities	47.6	30.9	54.8
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	-51.9	-21.6	-9.3
Loan repayment by related party	'	2.2	-11.7
(Loans to) repayments from affiliates	-1.7	-2.7	-0.3
Net cash proceeds (payments) from divestitures and asset sales	1.6	0.4	0.1
Net cash used in investing activities	-52	-21.7	-21.2
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	6.6	0	-0.9
Borrowings (repayments) of affiliated long-term debt	0	-2.2	2.8
Deferred financing costs	0	0	0
Dividends paid	-14.7	-4.9	-8.1
Stock issued and repurchased	0	0	'
Other financing receipts	2.3	3.7	'
Net cash provided by (used in) financing activities	-5.8	-3.4	-6.2
Effect of exchange rates on cash	0.5	2	-0.2
Net increase (decrease) in cash and cash equivalents	-9.7	7.8	27.2
Cash and cash equivalents at beginning of year	61.9	54.1	26.9
Cash and cash equivalents at end of period	52.2	61.9	54.1
Consolidating Adjustments [Member] | Senior Notes [Member]	'	'	'
Subsidiary, Sale of Stock [Line Items]	'	'	'
Cash provided by (used in) operating activities	-376.6	-32.5	-10.6
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	0	0	0
Loan repayment by related party	'	0	0
(Loans to) repayments from affiliates	-190.7	10.8	-17.6
Net cash proceeds (payments) from divestitures and asset sales	0	0	0
Net cash used in investing activities	-190.7	10.8	-17.6
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	0	0	0
Borrowings (repayments) of affiliated long-term debt	190.7	-10.8	17.6
Deferred financing costs	0	0	0
Dividends paid	376.6	32.5	10.6
Stock issued and repurchased	0	0	'
Other financing receipts	0	0	'
Net cash provided by (used in) financing activities	567.3	21.7	28.2
Effect of exchange rates on cash	0	0	0
Net increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of year	0	0	0
Cash and cash equivalents at end of period	$0	$0	$0

Subsidiary_Guarantor_Informati8

Subsidiary Guarantor Information for Shelf Registration - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Subsidiary Guarantor Information for Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'
Revolving credit facility	$350	'	'
Cash dividends paid	38.5	27.6	2.5
Subsidiary Guarantor Information for Shelf Registration [Member] | Revolving Credit Facility [Member]	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'
Restricted net assets	$147	'	'
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								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	$341.80	$395.20	$370.90	$370.40	$374.90	$387.90	$411.30	$380.90	$1,478.30	$1,555	$1,466.20
Selling, general and administrative	'	'	'	'	'	'	'	'	71.7	75.6	74.3
Operating profit (loss)	7.8	39.1	28.5	24.9	25.9	30.8	40.7	29.2	100.3	126.6	122.7
Other income (expense)	'	'	'	'	'	'	'	'	3.5	1.9	0.7
Equity income (loss) of subsidiaries	'	'	'	'	'	'	'	'	0.8	0.8	0.2
Interest expense	'	'	'	'	'	'	'	'	26.8	27.9	27.2
Income taxes	'	'	'	'	'	'	'	'	36.8	33.3	38.7
Income from continuing operations	-5.6	19.6	14.8	11.4	14.2	16.2	21.1	15.8	40.2	67.3	57.5
Discontinued operations	'	'	'	'	'	'	'	'	-0.1	-0.1	-19.9
Noncontrolling interests	'	'	'	'	'	'	'	'	0.3	-1.6	-0.7
Net income attributable to Koppers	-4.1	19.1	14.4	11	13.6	16	20.4	15.6	40.4	65.6	36.9
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	52.3	73.7	18.9
Shelf Registration [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	1,478.30	1,555	1,466.20
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	1,306.30	1,352.80	1,269.20
Selling, general and administrative	'	'	'	'	'	'	'	'	71.7	75.6	74.3
Operating profit (loss)	'	'	'	'	'	'	'	'	100.3	126.6	122.7
Other income (expense)	'	'	'	'	'	'	'	'	3.5	1.9	0.7
Equity income (loss) of subsidiaries	'	'	'	'	'	'	'	'	0	0	0
Interest expense	'	'	'	'	'	'	'	'	26.8	27.9	27.2
Income taxes	'	'	'	'	'	'	'	'	36.8	33.3	38.7
Income from continuing operations	'	'	'	'	'	'	'	'	40.2	67.3	57.5
Discontinued operations	'	'	'	'	'	'	'	'	-0.1	-0.1	-19.9
Noncontrolling interests	'	'	'	'	'	'	'	'	-0.3	1.6	0.7
Net income attributable to Koppers	'	'	'	'	'	'	'	'	40.4	65.6	36.9
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	52.3	73.7	18.9
Parent [Member] | Shelf Registration [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	0	0	0
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	0	0	0
Selling, general and administrative	'	'	'	'	'	'	'	'	1.9	1.6	1.2
Operating profit (loss)	'	'	'	'	'	'	'	'	-1.9	-1.6	-1.2
Other income (expense)	'	'	'	'	'	'	'	'	0	0	0
Equity income (loss) of subsidiaries	'	'	'	'	'	'	'	'	41.7	66.6	37.7
Interest expense	'	'	'	'	'	'	'	'	0	0	0
Income taxes	'	'	'	'	'	'	'	'	-0.6	-0.6	-0.4
Income from continuing operations	'	'	'	'	'	'	'	'	40.4	65.6	36.9
Discontinued operations	'	'	'	'	'	'	'	'	0	0	0
Noncontrolling interests	'	'	'	'	'	'	'	'	0	0	0
Net income attributable to Koppers	'	'	'	'	'	'	'	'	40.4	65.6	36.9
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	52.3	73.7	18.9
Koppers Inc. [Member] | Shelf Registration [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	843.7	893.2	854.1
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	745.4	786.6	762.9
Selling, general and administrative	'	'	'	'	'	'	'	'	41.5	45.1	41.6
Operating profit (loss)	'	'	'	'	'	'	'	'	56.8	61.5	49.6
Other income (expense)	'	'	'	'	'	'	'	'	1.3	0.4	0.3
Equity income (loss) of subsidiaries	'	'	'	'	'	'	'	'	17.5	40.8	22.9
Interest expense	'	'	'	'	'	'	'	'	26.7	27.4	27.4
Income taxes	'	'	'	'	'	'	'	'	7.3	8.7	7.7
Income from continuing operations	'	'	'	'	'	'	'	'	41.6	66.6	37.7
Discontinued operations	'	'	'	'	'	'	'	'	0.1	0	0
Noncontrolling interests	'	'	'	'	'	'	'	'	0	0	0
Net income attributable to Koppers	'	'	'	'	'	'	'	'	41.7	66.6	37.7
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	53.5	74.8	19.7
Domestic Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	61.8	97.5	72.6
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	43.5	78	55
Selling, general and administrative	'	'	'	'	'	'	'	'	0.7	2.1	1.8
Operating profit (loss)	'	'	'	'	'	'	'	'	17.6	17.4	15.8
Other income (expense)	'	'	'	'	'	'	'	'	4.2	6.1	5.5
Equity income (loss) of subsidiaries	'	'	'	'	'	'	'	'	11.4	28.8	1.3
Interest expense	'	'	'	'	'	'	'	'	0	0	0.1
Income taxes	'	'	'	'	'	'	'	'	16.4	12.5	0.8
Income from continuing operations	'	'	'	'	'	'	'	'	16.8	39.8	21.7
Discontinued operations	'	'	'	'	'	'	'	'	0	0	0
Noncontrolling interests	'	'	'	'	'	'	'	'	0	0	0
Net income attributable to Koppers	'	'	'	'	'	'	'	'	16.8	39.8	21.7
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	8.4	44	17.3
Foreign Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	462.7	480	443.6
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	413.3	414.6	364.2
Selling, general and administrative	'	'	'	'	'	'	'	'	22.1	23.4	26.2
Operating profit (loss)	'	'	'	'	'	'	'	'	27.3	42	53.2
Other income (expense)	'	'	'	'	'	'	'	'	0.9	0.2	0.1
Equity income (loss) of subsidiaries	'	'	'	'	'	'	'	'	-1.3	1.4	1.4
Interest expense	'	'	'	'	'	'	'	'	3.2	4.2	4.8
Income taxes	'	'	'	'	'	'	'	'	12.2	10.5	28.7
Income from continuing operations	'	'	'	'	'	'	'	'	11.5	28.9	21.2
Discontinued operations	'	'	'	'	'	'	'	'	-0.2	-0.1	-19.9
Noncontrolling interests	'	'	'	'	'	'	'	'	0	0	0
Net income attributable to Koppers	'	'	'	'	'	'	'	'	11.3	28.8	1.3
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	10.1	31.5	-3.7
Non-Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	162.1	158.6	147
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	156.2	147.6	138.2
Selling, general and administrative	'	'	'	'	'	'	'	'	5.5	3.4	3.5
Operating profit (loss)	'	'	'	'	'	'	'	'	0.4	7.6	5.3
Other income (expense)	'	'	'	'	'	'	'	'	1.2	0.4	0.3
Equity income (loss) of subsidiaries	'	'	'	'	'	'	'	'	0	0	0
Interest expense	'	'	'	'	'	'	'	'	1	1.5	0.5
Income taxes	'	'	'	'	'	'	'	'	1.5	2.2	1.9
Income from continuing operations	'	'	'	'	'	'	'	'	-0.9	4.3	3.2
Discontinued operations	'	'	'	'	'	'	'	'	0	0	0
Noncontrolling interests	'	'	'	'	'	'	'	'	-0.3	1.6	0.7
Net income attributable to Koppers	'	'	'	'	'	'	'	'	-0.6	2.7	2.5
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	0.4	2.8	3.5
Consolidating Adjustments [Member] | Shelf Registration [Member]	'	'	'	'	'	'	'	'	'	'	'
Subsidiary Guarantor Information For Subsidiary Senior Notes [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net sales	'	'	'	'	'	'	'	'	-52	-74.3	-51.1
Cost of sales including depreciation and amortization	'	'	'	'	'	'	'	'	-52.1	-74	-51.1
Selling, general and administrative	'	'	'	'	'	'	'	'	0	0	0
Operating profit (loss)	'	'	'	'	'	'	'	'	0.1	-0.3	0
Other income (expense)	'	'	'	'	'	'	'	'	-4.1	-5.2	-5.5
Equity income (loss) of subsidiaries	'	'	'	'	'	'	'	'	-69.3	-137.6	-63.3
Interest expense	'	'	'	'	'	'	'	'	-4.1	-5.2	-5.6
Income taxes	'	'	'	'	'	'	'	'	0	0	0
Income from continuing operations	'	'	'	'	'	'	'	'	-69.2	-137.9	-63.2
Discontinued operations	'	'	'	'	'	'	'	'	0	0	0
Noncontrolling interests	'	'	'	'	'	'	'	'	0	0	0
Net income attributable to Koppers	'	'	'	'	'	'	'	'	-69.2	-137.9	-63.2
Comprehensive income attributable to Koppers	'	'	'	'	'	'	'	'	($72.40)	($153.10)	($36.80)

Recovered_Sheet1

Subsidiary Guarantor Information for Shelf Registration - Condensed Consolidating Balance Sheet (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Millions, unless otherwise specified
ASSETS	'	'	'	'
Cash and cash equivalents	$82.20	$66.70	$54.10	$35.30
Receivables, net	157.9	162.7	'	'
Inventories, net	168.8	195.8	'	'
Deferred tax assets	10	15.1	'	'
Other current assets	35.7	29.8	'	'
Total current assets	473.1	481.2	'	'
Equity investments	6.6	5.8	'	'
Property, plant and equipment, net	197	161.1	'	'
Goodwill	72.7	75.6	72.1	'
Deferred tax assets	9.3	27.2	'	'
Other noncurrent assets	26.2	29.1	'	'
Total assets	784.9	780	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	107.6	103.5	'	'
Accrued liabilities	82.4	72.1	'	'
Total current liabilities	195.1	181.2	'	'
Long-term debt	303.1	296.1	'	'
Total liabilities	595.1	611.9	'	'
Koppers shareholders' equity	169.8	150.6	'	'
Noncontrolling interests	20	17.5	'	'
Total liabilities and equity	784.9	780	'	'
Shelf Registration [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	82.2	66.7	54.1	35.3
Receivables, net	166.9	164.3	'	'
Affiliated receivables	0	0	'	'
Inventories, net	168.8	195.8	'	'
Deferred tax assets	10	15.1	'	'
Other current assets	45.2	39.3	'	'
Total current assets	473.1	481.2	'	'
Equity investments	6.6	5.8	'	'
Property, plant and equipment, net	197	161.1	'	'
Goodwill	72.7	75.6	'	'
Deferred tax assets	9.3	27.2	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	26.2	29.1	'	'
Total assets	784.9	780	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	107.6	103.5	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	87.5	77.7	'	'
Total current liabilities	195.1	181.2	'	'
Long-term debt	303.1	296.1	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	96.9	134.6	'	'
Total liabilities	595.1	611.9	'	'
Koppers shareholders' equity	169.8	150.6	'	'
Noncontrolling interests	20	17.5	'	'
Total liabilities and equity	784.9	780	'	'
Parent [Member] | Shelf Registration [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	0.2	0.7	'	'
Inventories, net	0	0	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	0.2	0.7	'	'
Equity investments	174.7	154.9	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	0	0	'	'
Other noncurrent assets	0	0	'	'
Total assets	174.9	155.6	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0	0.1	'	'
Affiliated payables	0	0	'	'
Accrued liabilities	5.1	4.9	'	'
Total current liabilities	5.1	5	'	'
Long-term debt	0	0	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	5.1	5	'	'
Koppers shareholders' equity	169.8	150.6	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	174.9	155.6	'	'
Koppers Inc. [Member] | Shelf Registration [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	29.9	4.8	0	8.4
Receivables, net	75.6	80.2	'	'
Affiliated receivables	1.1	0	'	'
Inventories, net	86.1	102.2	'	'
Deferred tax assets	7.9	9.4	'	'
Other current assets	7.3	6.4	'	'
Total current assets	207.9	203	'	'
Equity investments	333.5	648.3	'	'
Property, plant and equipment, net	112.2	105.7	'	'
Goodwill	39.8	39.8	'	'
Deferred tax assets	2.4	14.9	'	'
Affiliated loan receivables	8.5	7.7	'	'
Other noncurrent assets	15	15.7	'	'
Total assets	719.3	1,035.10	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	48.3	51.4	'	'
Affiliated payables	1.9	120.8	'	'
Accrued liabilities	27.8	15.9	'	'
Total current liabilities	78	188.1	'	'
Long-term debt	296.5	296.1	'	'
Affiliated debt	109.5	301	'	'
Other long-term liabilities	67.6	101.2	'	'
Total liabilities	551.6	886.4	'	'
Koppers shareholders' equity	167.7	148.7	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	719.3	1,035.10	'	'
Domestic Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	0.1	0	0	0
Receivables, net	9.3	6.3	'	'
Affiliated receivables	3.9	119	'	'
Inventories, net	0	0	'	'
Deferred tax assets	1.5	5.5	'	'
Other current assets	0.6	2.8	'	'
Total current assets	15.4	133.6	'	'
Equity investments	182.9	183.8	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	-1.4	2.1	'	'
Affiliated loan receivables	123.8	326.3	'	'
Other noncurrent assets	0	0	'	'
Total assets	320.7	645.8	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	6.7	1.7	'	'
Affiliated payables	4	7.6	'	'
Accrued liabilities	0.5	12.2	'	'
Total current liabilities	11.2	21.5	'	'
Long-term debt	0	0	'	'
Affiliated debt	8.5	7.7	'	'
Other long-term liabilities	2.5	2.4	'	'
Total liabilities	22.2	31.6	'	'
Koppers shareholders' equity	298.5	614.2	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	320.7	645.8	'	'
Foreign Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	43.5	40.7	45.1	17
Receivables, net	55.5	63.5	'	'
Affiliated receivables	0.8	2.3	'	'
Inventories, net	75.2	86.7	'	'
Deferred tax assets	0	0	'	'
Other current assets	17.5	17.6	'	'
Total current assets	192.5	210.8	'	'
Equity investments	50.5	43	'	'
Property, plant and equipment, net	38.1	40.7	'	'
Goodwill	31.5	34.4	'	'
Deferred tax assets	5.5	7.6	'	'
Affiliated loan receivables	0.1	0.1	'	'
Other noncurrent assets	9.9	12.1	'	'
Total assets	328.1	348.7	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	40.6	40.6	'	'
Affiliated payables	0.4	1.4	'	'
Accrued liabilities	31.4	35.8	'	'
Total current liabilities	72.4	77.8	'	'
Long-term debt	0	0	'	'
Affiliated debt	55.2	64.5	'	'
Other long-term liabilities	19.6	24.5	'	'
Total liabilities	147.2	166.8	'	'
Koppers shareholders' equity	180.9	181.9	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	328.1	348.7	'	'
Non-Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	8.7	21.2	9	9.9
Receivables, net	26.5	14.3	'	'
Affiliated receivables	1.6	6.9	'	'
Inventories, net	7.7	7.2	'	'
Deferred tax assets	0.6	0.2	'	'
Other current assets	19.8	12.5	'	'
Total current assets	64.9	62.3	'	'
Equity investments	4.5	4	'	'
Property, plant and equipment, net	46.7	14.7	'	'
Goodwill	1.4	1.4	'	'
Deferred tax assets	2.8	2.6	'	'
Affiliated loan receivables	40.8	39.2	'	'
Other noncurrent assets	1.3	1.3	'	'
Total assets	162.4	125.5	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	12	9.7	'	'
Affiliated payables	8.4	8.9	'	'
Accrued liabilities	22.7	8.9	'	'
Total current liabilities	43.1	27.5	'	'
Long-term debt	6.6	0	'	'
Affiliated debt	0	0	'	'
Other long-term liabilities	7.2	6.5	'	'
Total liabilities	56.9	34	'	'
Koppers shareholders' equity	85.5	74	'	'
Noncontrolling interests	20	17.5	'	'
Total liabilities and equity	162.4	125.5	'	'
Consolidating Adjustments [Member] | Shelf Registration [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0	'	'
Affiliated receivables	-7.6	-128.9	'	'
Inventories, net	-0.2	-0.3	'	'
Deferred tax assets	0	0	'	'
Other current assets	0	0	'	'
Total current assets	-7.8	-129.2	'	'
Equity investments	-739.5	-1,028.20	'	'
Property, plant and equipment, net	0	0	'	'
Goodwill	0	0	'	'
Deferred tax assets	0	0	'	'
Affiliated loan receivables	-173.2	-373.3	'	'
Other noncurrent assets	0	0	'	'
Total assets	-920.5	-1,530.70	'	'
LIABILITIES AND EQUITY	'	'	'	'
Accounts payable	0	0	'	'
Affiliated payables	-14.7	-138.7	'	'
Accrued liabilities	0	0	'	'
Total current liabilities	-14.7	-138.7	'	'
Long-term debt	0	0	'	'
Affiliated debt	-173.2	-373.2	'	'
Other long-term liabilities	0	0	'	'
Total liabilities	-187.9	-511.9	'	'
Koppers shareholders' equity	-732.6	-1,018.80	'	'
Noncontrolling interests	0	0	'	'
Total liabilities and equity	($920.50)	($1,530.70)	'	'

Recovered_Sheet2

Subsidiary Guarantor Information for Shelf Registration - Condensed Consolidating Statement of Cash Flows (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'	'
Cash provided by (used in) operating activities	$117.60	$77.80	$76.90
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	-72.9	-28.9	-33.2
Loan repayment by related party	0	2.2	-11.7
Net cash proceeds from divestitures and asset sales	2.9	0.8	0.8
Net cash provided by (used in) investing activities	-72.3	-39.9	-44.7
Cash provided by (used in) financing activities:	'	'	'
Deferred financing costs	-1.3	-0.1	-0.5
Dividends paid	-21.1	-19.5	-18.2
Net cash provided by (used in) financing activities	-30.3	-27.3	-13.3
Effect of exchange rates on cash	0.5	2	-0.1
Net increase (decrease) in cash and cash equivalents	15.5	12.6	18.8
Cash and cash equivalents at beginning of year	66.7	54.1	35.3
Cash and cash equivalents at end of period	82.2	66.7	54.1
Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'	'
Cash provided by (used in) operating activities	117.6	77.8	76.9
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	-75.2	-42.9	-33.8
Loan repayment by related party	'	2.2	-11.7
(Loans to) repayments from affiliates	0	0	0
Net cash proceeds from divestitures and asset sales	2.9	0.8	0.8
Net cash provided by (used in) investing activities	-72.3	-39.9	-44.7
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	6.6	-6.4	5.4
Borrowings (repayments) of affiliated long-term debt	0	0	0
Deferred financing costs	-1.3	-0.1	-0.5
Dividends paid	-21.1	-19.5	-18.2
Stock issued and repurchased	-17.3	-6.6	'
Other financing receipts	2.8	5.3	'
Net cash provided by (used in) financing activities	-30.3	-27.3	-13.3
Effect of exchange rates on cash	0.5	2	-0.1
Net increase (decrease) in cash and cash equivalents	15.5	12.6	18.8
Cash and cash equivalents at beginning of year	66.7	54.1	35.3
Cash and cash equivalents at end of period	82.2	66.7	54.1
Parent [Member] | Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'	'
Cash provided by (used in) operating activities	37.8	26.1	18.2
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	0	0	0
Loan repayment by related party	'	0	0
(Loans to) repayments from affiliates	0	0	0
Net cash proceeds from divestitures and asset sales	0	0	0
Net cash provided by (used in) investing activities	0	0	0
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	0	0	0
Borrowings (repayments) of affiliated long-term debt	0	0	0
Deferred financing costs	0	0	0
Dividends paid	-20.5	-19.5	-18.2
Stock issued and repurchased	-17.3	-6.6	'
Other financing receipts	0	0	'
Net cash provided by (used in) financing activities	-37.8	-26.1	-18.2
Effect of exchange rates on cash	0	0	0
Net increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of year	0	0	0
Cash and cash equivalents at end of period	0	0	0
Koppers Inc. [Member] | Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'	'
Cash provided by (used in) operating activities	278.7	44.6	30
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	-23.3	-21.3	-24.5
Loan repayment by related party	'	0	0
(Loans to) repayments from affiliates	-0.8	0.3	1.2
Net cash proceeds from divestitures and asset sales	1.3	0.4	0.7
Net cash provided by (used in) investing activities	-22.8	-20.6	-22.6
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	0	-6.4	6.3
Borrowings (repayments) of affiliated long-term debt	-191.5	13.3	-19.2
Deferred financing costs	-1.3	-0.1	-0.5
Dividends paid	-38.5	-27.6	-2.5
Stock issued and repurchased	0	0	'
Other financing receipts	0.5	1.6	'
Net cash provided by (used in) financing activities	-230.8	-19.2	-15.9
Effect of exchange rates on cash	0	0	0.1
Net increase (decrease) in cash and cash equivalents	25.1	4.8	-8.4
Cash and cash equivalents at beginning of year	4.8	0	8.4
Cash and cash equivalents at end of period	29.9	4.8	0
Domestic Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'	'
Cash provided by (used in) operating activities	130.1	8.7	-15.5
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	0	0	0
Loan repayment by related party	'	0	0
(Loans to) repayments from affiliates	193.2	-8.4	16.7
Net cash proceeds from divestitures and asset sales	0	0	0
Net cash provided by (used in) investing activities	193.2	-8.4	16.7
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	0	0	0
Borrowings (repayments) of affiliated long-term debt	0.8	-0.3	-1.2
Deferred financing costs	0	0	0
Dividends paid	-324	0	0
Stock issued and repurchased	0	0	'
Other financing receipts	0	0	'
Net cash provided by (used in) financing activities	-323.2	-0.3	-1.2
Effect of exchange rates on cash	0	0	0
Net increase (decrease) in cash and cash equivalents	0.1	0	0
Cash and cash equivalents at beginning of year	0	0	0
Cash and cash equivalents at end of period	0.1	0	0
Foreign Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'	'
Cash provided by (used in) operating activities	39.9	29.5	49.5
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	-22.1	-31.5	-8.6
Loan repayment by related party	'	0	0
(Loans to) repayments from affiliates	0	0	0
Net cash proceeds from divestitures and asset sales	1.1	0.4	0.1
Net cash provided by (used in) investing activities	-21	-31.1	-8.5
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	0	0	-0.9
Borrowings (repayments) of affiliated long-term debt	0	0	-3.5
Deferred financing costs	0	0	0
Dividends paid	-14.1	-4.9	-8.1
Stock issued and repurchased	0	0	'
Other financing receipts	0	0	'
Net cash provided by (used in) financing activities	-14.1	-4.9	-12.5
Effect of exchange rates on cash	-2	2.1	-0.4
Net increase (decrease) in cash and cash equivalents	2.8	-4.4	28.1
Cash and cash equivalents at beginning of year	40.7	45.1	17
Cash and cash equivalents at end of period	43.5	40.7	45.1
Non-Guarantor Subsidiaries [Member] | Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'	'
Cash provided by (used in) operating activities	7.7	1.4	5.3
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	-37.5	-0.5	-0.7
Loan repayment by related party	'	2.2	-11.7
(Loans to) repayments from affiliates	-1.7	-2.7	-0.3
Net cash proceeds from divestitures and asset sales	0.5	0	0
Net cash provided by (used in) investing activities	-38.7	-1	-12.7
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	6.6	0	0
Borrowings (repayments) of affiliated long-term debt	0	-2.2	6.3
Deferred financing costs	0	0	0
Dividends paid	-0.6	0	0
Stock issued and repurchased	7.7	10.4	'
Other financing receipts	2.3	3.7	'
Net cash provided by (used in) financing activities	16	11.9	6.3
Effect of exchange rates on cash	2.5	-0.1	0.2
Net increase (decrease) in cash and cash equivalents	-12.5	12.2	-0.9
Cash and cash equivalents at beginning of year	21.2	9	9.9
Cash and cash equivalents at end of period	8.7	21.2	9
Consolidating Adjustments [Member] | Shelf Registration [Member]	'	'	'
Subsidiary Guarantor Information for Shelf Registration [Line Items]	'	'	'
Cash provided by (used in) operating activities	-376.6	-32.5	-10.6
Cash provided by (used in) investing activities:	'	'	'
Capital expenditures and acquisitions	7.7	10.4	0
Loan repayment by related party	'	0	0
(Loans to) repayments from affiliates	-190.7	10.8	-17.6
Net cash proceeds from divestitures and asset sales	0	0	0
Net cash provided by (used in) investing activities	-183	21.2	-17.6
Cash provided by (used in) financing activities:	'	'	'
Borrowings (repayments) of long-term debt	0	0	0
Borrowings (repayments) of affiliated long-term debt	190.7	-10.8	17.6
Deferred financing costs	0	0	0
Dividends paid	376.6	32.5	10.6
Stock issued and repurchased	-7.7	-10.4	'
Other financing receipts	0	0	'
Net cash provided by (used in) financing activities	559.6	11.3	28.2
Effect of exchange rates on cash	0	0	0
Net increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of year	0	0	0
Cash and cash equivalents at end of period	$0	$0	$0

Schedule_II_Valuation_and_Qual1

Schedule II - Valuation and Qualifying Accounts (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Allowance for Doubtful Accounts [Member]	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Balance at Beginning of Year	$3.70	$0.30	$0.10
Increase (Decrease) to Expense	-0.2	3.2	0.3
Net (Write-Offs) Recoveries	0	0	-0.1
Currency Translation	0.1	0.2	0
Balance at End of Year	3.6	3.7	0.3
Inventory Obsolescence Reserves [Member]	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Balance at Beginning of Year	1.1	1.4	2.1
Increase (Decrease) to Expense	0.7	0.5	4.2
Net (Write-Offs) Recoveries	0	-0.8	-4.9
Currency Translation	-0.1	0	0
Balance at End of Year	1.7	1.1	1.4
Deferred Tax Valuation Allowance [Member]	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Balance at Beginning of Year	17.4	10.2	11.4
Increase (Decrease) to Expense	2.6	8.8	-1.2
Net (Write-Offs) Recoveries	-0.2	-1.6	0
Currency Translation	-0.1	0	0
Balance at End of Year	$19.70	$17.40	$10.20