Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Statement of Cash Flows (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Subsidiary Guarantor Senior Notes [Line Items]
Cash provided by (used in) operating activities	$ 65.6	$ 54.5
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(29.4)	(15.8)
Net cash proceeds (payments) from divestitures and asset sales	2.4	0.7
Net cash provided by (used in) investing activities	(27.0)	(15.1)
Cash provided by (used in) financing activities:
Deferred financing costs	(1.2)	(0.1)
Dividends paid	(15.3)	(14.5)
Net cash provided by (used in) financing activities	(31.5)	(27.0)
Effect of exchange rates on cash	(1.4)	2.4
Net increase (decrease) in cash and cash equivalents	5.7	14.8
Cash and cash equivalents at beginning of year	66.7	54.1
Cash and cash equivalents at end of period	72.4	68.9
Senior Notes [Member]
Subsidiary Guarantor Senior Notes [Line Items]
Cash provided by (used in) operating activities	65.6	54.5
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(29.4)	(15.8)
Net cash proceeds (payments) from divestitures and asset sales	2.4	0.7
Net cash provided by (used in) investing activities	(27.0)	(15.1)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		(5.0)
Deferred financing costs	(1.2)	(0.1)
Dividends paid	(15.3)	(14.5)
Other financing activities	2.3
Stock issued (repurchased)	(17.3)	(7.4)
Net cash provided by (used in) financing activities	(31.5)	(27.0)
Effect of exchange rates on cash	(1.4)	2.4
Net increase (decrease) in cash and cash equivalents	5.7	14.8
Cash and cash equivalents at beginning of year	66.7	54.1
Cash and cash equivalents at end of period	72.4	68.9
Parent [Member] | Senior Notes [Member]
Subsidiary Guarantor Senior Notes [Line Items]
Cash provided by (used in) operating activities	32.6	21.8
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	0	0
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0.1
Deferred financing costs	0	0
Dividends paid	(15.3)	(14.5)
Other financing activities	0
Stock issued (repurchased)	(17.3)	(7.4)
Net cash provided by (used in) financing activities	(32.6)	(21.8)
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	0	0
Koppers Inc. [Member] | Senior Notes [Member]
Subsidiary Guarantor Senior Notes [Line Items]
Cash provided by (used in) operating activities	39.7	32.0
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(13.3)	(12.2)
Net cash proceeds (payments) from divestitures and asset sales	1.4	0.3
Net cash provided by (used in) investing activities	(11.9)	(11.9)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		(5.0)
Deferred financing costs	(1.2)	(0.1)
Dividends paid	(23.5)	(14.8)
Other financing activities	0
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	(24.7)	(19.9)
Effect of exchange rates on cash	0.1	(0.1)
Net increase (decrease) in cash and cash equivalents	3.2	0.1
Cash and cash equivalents at beginning of year	4.8	0
Cash and cash equivalents at end of period	8.0	0.1
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]
Subsidiary Guarantor Senior Notes [Line Items]
Cash provided by (used in) operating activities	0	0
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	0	0
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0
Deferred financing costs	0	0
Dividends paid	0	0
Other financing activities	0
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	0	0
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	0	0
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]
Subsidiary Guarantor Senior Notes [Line Items]
Cash provided by (used in) operating activities	16.8	15.5
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	(16.1)	(3.6)
Net cash proceeds (payments) from divestitures and asset sales	1.0	0.4
Net cash provided by (used in) investing activities	(15.1)	(3.2)
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		(0.1)
Deferred financing costs	0	0
Dividends paid	0	0
Other financing activities	2.3
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	2.3	(0.1)
Effect of exchange rates on cash	(1.5)	2.5
Net increase (decrease) in cash and cash equivalents	2.5	14.7
Cash and cash equivalents at beginning of year	61.9	54.1
Cash and cash equivalents at end of period	64.4	68.8
Consolidating Adjustments [Member] | Senior Notes [Member]
Subsidiary Guarantor Senior Notes [Line Items]
Cash provided by (used in) operating activities	(23.5)	(14.8)
Cash provided by (used in) investing activities:
Capital expenditures and acquisitions	0	0
Net cash proceeds (payments) from divestitures and asset sales	0	0
Net cash provided by (used in) investing activities	0	0
Cash provided by (used in) financing activities:
Borrowings (repayments) of long-term debt		0
Deferred financing costs	0	0
Dividends paid	23.5	14.8
Other financing activities	0
Stock issued (repurchased)	0	0
Net cash provided by (used in) financing activities	23.5	14.8
Effect of exchange rates on cash	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	$ 0	$ 0