Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Statement of Cash Flows (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
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	(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	(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	(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	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	(52.0)	(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	(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