Subsidiary Guarantor Information for Koppers Inc. Senior Notes and Shelf Registration - Condensed Consolidating Statement of Cash Flows (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	$ 77.8	$ 76.9	$ 105.3
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(28.9)	(33.2)	(29.9)
Loan to related party	2.2	(11.7)	0
Net cash proceeds (payments) from divestitures and asset sales	0.8	0.8	2.0
Net cash provided by (used in) investing activities	(39.9)	(44.7)	(63.4)
Cash provided by (used in) financing activities:
Deferred financing costs	(0.1)	(0.5)	(0.4)
Dividends paid	(19.5)	(18.2)	(23.1)
Stock repurchased	(8.1)	(0.3)	(0.9)
Net cash used in financing activities	(27.3)	(13.3)	(64.3)
Effect of exchange rates on cash	2.0	(0.1)	(0.7)
Net decrease in cash and cash equivalents	12.6	18.8	(23.1)
Cash and cash equivalents at beginning of year	54.1	35.3	58.4
Cash and cash equivalents at end of year	66.7	54.1	35.3
Senior Notes [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	77.8	76.9	105.3
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(42.9)	(33.8)	(65.4)
Loan to related party	2.2	(11.7)
Net cash proceeds (payments) from divestitures and asset sales	0.8	0.8	2.0
Net cash provided by (used in) investing activities	(39.9)	(44.7)	(63.4)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	(6.4)	5.4	(40.2)
Deferred financing costs	(0.1)	(0.5)	(0.4)
Dividends paid	(19.5)	(18.2)	(23.1)
Stock repurchased	(6.6)
Stock issued (repurchased)			(0.6)
Other financing receipts	5.3
Net cash used in financing activities	(27.3)	(13.3)	(64.3)
Effect of exchange rates on cash	2.0	(0.1)	(0.7)
Net decrease in cash and cash equivalents	12.6	18.8	(23.1)
Cash and cash equivalents at beginning of year	54.1	35.3	58.4
Cash and cash equivalents at end of year	66.7	54.1	35.3
Shelf Registration [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	77.8	76.9	105.3
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(42.9)	(33.8)	(65.4)
Loan to related party	2.2	(11.7)
Net cash proceeds (payments) from divestitures and asset sales	0.8	0.8	2.0
Net cash provided by (used in) investing activities	(39.9)	(44.7)	(63.4)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	(6.4)	5.4	(40.2)
Deferred financing costs	(0.1)	(0.5)	(0.4)
Dividends paid	(19.5)	(18.2)	(23.1)
Stock issued (repurchased)	(6.6)		(0.6)
Other financing receipts	5.3
Net cash used in financing activities	(27.3)	(13.3)	(64.3)
Effect of exchange rates on cash	2.0	(0.1)	(0.7)
Net decrease in cash and cash equivalents	12.6	18.8	(23.1)
Cash and cash equivalents at beginning of year	54.1	35.3	58.4
Cash and cash equivalents at end of year	66.7	54.1	35.3
Parent [Member] | Senior Notes [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	26.0	18.1	18.7
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0	0
Loan to related party	0	0
Net cash proceeds (payments) 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
Deferred financing costs	0	0	0
Dividends paid	(19.5)	(18.1)	(18.1)
Stock repurchased	(6.5)
Stock issued (repurchased)			(0.8)
Other financing receipts	0
Net cash used in financing activities	(26.0)	(18.1)	(18.9)
Effect of exchange rates on cash	0	0	0
Net decrease in cash and cash equivalents	0	0	(0.2)
Cash and cash equivalents at beginning of year	0	0	0.2
Cash and cash equivalents at end of year	0	0	0
Parent [Member] | Shelf Registration [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	26.0	18.1	18.7
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0	0
Loan to related party	0	0
Net cash proceeds (payments) 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
Deferred financing costs	0	0	0
Dividends paid	(19.5)	(18.1)	(18.1)
Stock issued (repurchased)	(6.5)		(0.8)
Other financing receipts	0
Net cash used in financing activities	(26.0)	(18.1)	(18.9)
Effect of exchange rates on cash	0	0	0
Net decrease in cash and cash equivalents	0	0	(0.2)
Cash and cash equivalents at beginning of year	0	0	0.2
Cash and cash equivalents at end of year	0	0	0
Koppers Inc. [Member] | Senior Notes [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	50.5	9.5	75.2
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(21.3)	(24.5)	(35.0)
Loan to related party	0	0
Net cash proceeds (payments) from divestitures and asset sales	0.4	0.7	0.2
Net cash provided by (used in) investing activities	(20.9)	(23.8)	(34.8)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	(6.4)	6.3	(40.2)
Deferred financing costs	(0.1)	(0.5)	(0.4)
Dividends paid	(19.8)	0	(4.5)
Stock repurchased	(0.1)
Stock issued (repurchased)			0.2
Other financing receipts	1.6
Net cash used in financing activities	(24.8)	5.8	(44.9)
Effect of exchange rates on cash	0	0.1	0
Net decrease in cash and cash equivalents	4.8	(8.4)	(4.5)
Cash and cash equivalents at beginning of year	0	8.4	12.9
Cash and cash equivalents at end of year	4.8	0	8.4
Koppers Inc. [Member] | Shelf Registration [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	50.5	9.5	75.2
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(21.3)	(24.5)	(35.0)
Loan to related party	0	0
Net cash proceeds (payments) from divestitures and asset sales	0.4	0.7	0.2
Net cash provided by (used in) investing activities	(20.9)	(23.8)	(34.8)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	(6.4)	6.3	(40.2)
Deferred financing costs	(0.1)	(0.5)	(0.4)
Dividends paid	(19.8)	0	(4.5)
Stock issued (repurchased)	(0.1)		0.2
Other financing receipts	1.6
Net cash used in financing activities	(24.8)	5.8	(44.9)
Effect of exchange rates on cash	0	0.1	0
Net decrease in cash and cash equivalents	4.8	(8.4)	(4.5)
Cash and cash equivalents at beginning of year	0	8.4	12.9
Cash and cash equivalents at end of year	4.8	0	8.4
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	0	0	0
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0	0
Loan to related party	0	0
Net cash proceeds (payments) 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
Deferred financing costs	0	0	0
Dividends paid	0	0	0
Stock repurchased	0
Stock issued (repurchased)			0
Other financing receipts	0
Net cash used in financing activities	0	0	0
Effect of exchange rates on cash	0	0	0
Net 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 year	0	0	0
Domestic Guarantor Subsidiaries [Member] | Shelf Registration [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	0	0	0
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0	0
Loan to related party	0	0
Net cash proceeds (payments) 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
Deferred financing costs	0	0	0
Dividends paid	0	0	0
Stock issued (repurchased)	0		0
Other financing receipts	0
Net cash used in financing activities	0	0	0
Effect of exchange rates on cash	0	0	0
Net 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 year	0	0	0
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	21.1	49.3	15.9
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(21.6)	(9.3)	(30.4)
Loan to related party	2.2	(11.7)
Net cash proceeds (payments) from divestitures and asset sales	0.4	0.1	1.8
Net cash provided by (used in) investing activities	(19.0)	(20.9)	(28.6)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	0	(0.9)	0
Deferred financing costs	0	0	0
Dividends paid	0	(0.1)	(5.0)
Stock repurchased	0
Stock issued (repurchased)			0
Other financing receipts	3.7
Net cash used in financing activities	3.7	(1.0)	(5.0)
Effect of exchange rates on cash	2.0	(0.2)	(0.7)
Net decrease in cash and cash equivalents	7.8	27.2	(18.4)
Cash and cash equivalents at beginning of year	54.1	26.9	45.3
Cash and cash equivalents at end of year	61.9	54.1	26.9
Non-Guarantor Subsidiaries [Member] | Shelf Registration [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	6.9	11.4	6.8
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(0.5)	(0.7)	(0.4)
Loan to related party	2.2	(11.7)
Net cash proceeds (payments) from divestitures and asset sales	0	0	0.1
Net cash provided by (used in) investing activities	1.7	(12.4)	(0.3)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	0	0	0
Deferred financing costs	0	0	0
Dividends paid	0	(0.1)	(5.0)
Stock issued (repurchased)	0		0
Other financing receipts	3.7
Net cash used in financing activities	3.7	(0.1)	(5.0)
Effect of exchange rates on cash	(0.1)	0.2	0
Net decrease in cash and cash equivalents	12.2	(0.9)	1.5
Cash and cash equivalents at beginning of year	9.0	9.9	8.4
Cash and cash equivalents at end of year	21.2	9.0	9.9
Consolidating Adjustments [Member] | Senior Notes [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	(19.8)	0	(4.5)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0	0
Loan to related party	0	0
Net cash proceeds (payments) 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
Deferred financing costs	0	0	0
Dividends paid	19.8	0	4.5
Stock repurchased	0
Stock issued (repurchased)			0
Other financing receipts	0
Net cash used in financing activities	19.8	0	4.5
Effect of exchange rates on cash	0	0	0
Net 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 year	0	0	0
Consolidating Adjustments [Member] | Shelf Registration [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	(19.8)	0	(4.5)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0	0
Loan to related party	0	0
Net cash proceeds (payments) 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
Deferred financing costs	0	0	0
Dividends paid	19.8	0	4.5
Stock issued (repurchased)	0		0
Other financing receipts	0
Net cash used in financing activities	19.8	0	4.5
Effect of exchange rates on cash	0	0	0
Net 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 year	0	0	0
Foreign Guarantor Subsidiaries [Member] | Shelf Registration [Member]
Subsidiary, Sale of Stock [Line Items]
Cash provided by (used in) operating activities	14.2	37.9	9.1
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(21.1)	(8.6)	(30.0)
Loan to related party	0	0
Net cash proceeds (payments) from divestitures and asset sales	0.4	0.1	1.7
Net cash provided by (used in) investing activities	(20.7)	(8.5)	(28.3)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt	0	(0.9)	0
Deferred financing costs	0	0	0
Dividends paid	0	0	0
Stock issued (repurchased)	0		0
Other financing receipts	0
Net cash used in financing activities	0	(0.9)	0
Effect of exchange rates on cash	2.1	(0.4)	(0.7)
Net decrease in cash and cash equivalents	(4.4)	28.1	(19.9)
Cash and cash equivalents at beginning of year	45.1	17.0	36.9
Cash and cash equivalents at end of year	$ 40.7	$ 45.1	$ 17.0