Subsidiary Guarantor Information for Shelf Registration - Condensed Consolidating Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
ASSETS
Cash and cash equivalents	$ 82.2	$ 66.7	$ 54.1	$ 35.3
Receivables, net	157.9	162.7
Inventories, net	168.8	195.8
Deferred tax assets	10.0	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	197.0	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	780.0
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	20.0	17.5
Total liabilities and equity	784.9	780.0
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	10.0	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	197.0	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	780.0
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	20.0	17.5
Total liabilities and equity	784.9	780.0
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	5.0
Long-term debt	0	0
Affiliated debt	0	0
Other long-term liabilities	0	0
Total liabilities	5.1	5.0
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	203.0
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	15.0	15.7
Total assets	719.3	1,035.1
LIABILITIES AND EQUITY
Accounts payable	48.3	51.4
Affiliated payables	1.9	120.8
Accrued liabilities	27.8	15.9
Total current liabilities	78.0	188.1
Long-term debt	296.5	296.1
Affiliated debt	109.5	301.0
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	1,035.1
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	119.0
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	4.0	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	17.0
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	43.0
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	9.0	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	4.0
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	12.0	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	34.0
Koppers shareholders' equity	85.5	74.0
Noncontrolling interests	20.0	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)	(1,028.2)
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)	(1,530.7)
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)	(1,018.8)
Noncontrolling interests	0	0
Total liabilities and equity	$ (920.5)	$ (1,530.7)