Subsidiary Guarantor Information for Koppers Inc. Senior Notes - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Assets
Cash and cash equivalents	$ 51.2	$ 51.1	$ 54.4	$ 82.2
Receivables, net	204.8	198.7
Inventories, net	223.4	241.2
Deferred tax assets	13.6	10.5
Other current assets	33.9	30.3
Total current assets	538.2	541.3
Equity investments	3.9	5.0
Property, plant and equipment, net	291.9	299.7
Goodwill	256.6	247.2
Intangible assets, net	165.2	167.7
Deferred tax assets	8.3	7.8
Other noncurrent assets	26.0	25.2
Total assets	1,290.1	1,293.9
LIABILITIES AND EQUITY
Accounts payable	170.8	120.6
Accrued liabilities	95.3	122.5
Short-term debt and current portion of long-term debt	45.4	43.9
Total current liabilities	311.5	292.1
Long-term debt	748.8	806.6
Other long-term liabilities	87.3	46.4
Total liabilities	1,211.2	1,210.0
Koppers shareholders' equity	70.4	70.0
Noncontrolling interests	8.5	13.9
Total liabilities and equity	1,290.1	1,293.9
Senior Notes [Member]
Assets
Cash and cash equivalents	51.2	51.1	54.4	82.2
Receivables, net	206.6	198.7
Affiliated receivables	0.0	0.0
Inventories, net	223.4	241.2
Deferred tax assets	13.6	10.5
Other current assets	43.4	39.8
Total current assets	538.2	541.3
Equity investments	3.9	5.0
Property, plant and equipment, net	291.9	299.7
Goodwill	256.6	247.2
Intangible assets, net	165.2	167.7
Deferred tax assets	8.3	7.8
Affiliated loan receivables	0.0	0.0
Other noncurrent assets	26.0	25.2
Total assets	1,290.1	1,293.9
LIABILITIES AND EQUITY
Accounts payable	170.8	120.6
Affiliated payables	0.0	0.0
Accrued liabilities	95.3	127.6
Short-term debt and current portion of long-term debt	45.4	43.9
Total current liabilities	311.5	292.1
Long-term debt	748.8	806.6
Affiliated debt	0.0	0.0
Other long-term liabilities	150.9	111.3
Total liabilities	1,211.2	1,210.0
Koppers shareholders' equity	70.4	70.0
Noncontrolling interests	8.5	13.9
Total liabilities and equity	1,290.1	1,293.9
Senior Notes [Member] | Intersegment [Member]
Assets
Cash and cash equivalents	0.0	0.0	0.0	0.0
Receivables, net	0.0	0.0
Affiliated receivables	(44.3)	(15.9)
Inventories, net	(2.7)	(1.0)
Deferred tax assets	0.0	0.0
Other current assets	0.0	0.0
Total current assets	(47.0)	(16.9)
Equity investments	(1,076.1)	(1,053.8)
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Intangible assets, net	0.0	0.0
Deferred tax assets	0.0	0.0
Affiliated loan receivables	(310.5)	(293.4)
Other noncurrent assets	0.0	0.0
Total assets	(1,433.6)	(1,364.1)
LIABILITIES AND EQUITY
Accounts payable	0.0	0.0
Affiliated payables	(51.7)	(29.4)
Accrued liabilities	0.0	0.0
Short-term debt and current portion of long-term debt	0.0	0.0
Total current liabilities	(51.7)	(29.4)
Long-term debt	0.0	0.0
Affiliated debt	(310.5)	(293.4)
Other long-term liabilities	0.0	0.0
Total liabilities	(362.2)	(322.8)
Koppers shareholders' equity	(1,071.4)	(1,041.3)
Noncontrolling interests	0.0	0.0
Total liabilities and equity	(1,433.6)	(1,364.1)
Parent [Member] | Senior Notes [Member]
Assets
Cash and cash equivalents	0.0	0.0	0.0	0.0
Receivables, net	0.0	0.0
Affiliated receivables	0.0	0.8
Inventories, net	0.0	0.0
Deferred tax assets	0.0	0.0
Other current assets	0.0	0.0
Total current assets	0.0	0.8
Equity investments	69.9	74.5
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Intangible assets, net	0.0	0.0
Deferred tax assets	0.0	0.0
Affiliated loan receivables	0.0	0.0
Other noncurrent assets	0.0	0.0
Total assets	69.9	75.3
LIABILITIES AND EQUITY
Accounts payable	0.1	0.1
Affiliated payables	0.0	0.0
Accrued liabilities	(0.6)	5.2
Short-term debt and current portion of long-term debt	0.0	0.0
Total current liabilities	(0.5)	5.3
Long-term debt	0.0	0.0
Affiliated debt	0.0	0.0
Other long-term liabilities	0.0	0.0
Total liabilities	(0.5)	5.3
Koppers shareholders' equity	70.4	70.0
Noncontrolling interests	0.0	0.0
Total liabilities and equity	69.9	75.3
Koppers Inc. [Member] | Senior Notes [Member]
Assets
Cash and cash equivalents	0.3	0.0	0.0	29.9
Receivables, net	83.3	75.7
Affiliated receivables	15.1	4.5
Inventories, net	98.8	108.8
Deferred tax assets	10.1	8.0
Other current assets	4.9	3.0
Total current assets	212.5	200.0
Equity investments	792.6	767.2
Property, plant and equipment, net	120.4	121.2
Goodwill	43.9	39.8
Intangible assets, net	9.4	2.2
Deferred tax assets	(3.4)	(1.0)
Affiliated loan receivables	30.9	40.5
Other noncurrent assets	19.1	19.1
Total assets	1,225.4	1,189.0
LIABILITIES AND EQUITY
Accounts payable	77.7	60.9
Affiliated payables	28.4	13.2
Accrued liabilities	33.8	37.9
Short-term debt and current portion of long-term debt	30.3	30.0
Total current liabilities	170.2	142.0
Long-term debt	706.1	764.0
Affiliated debt	209.6	145.5
Other long-term liabilities	68.2	68.6
Total liabilities	1,154.1	1,120.1
Koppers shareholders' equity	71.3	68.9
Noncontrolling interests	0.0	0.0
Total liabilities and equity	1,225.4	1,189.0
Domestic Guarantor Subsidiaries [Member] | Senior Notes [Member]
Assets
Cash and cash equivalents	0.5	0.9	0.0	0.1
Receivables, net	35.3	20.0
Affiliated receivables	10.7	9.3
Inventories, net	27.3	30.8
Deferred tax assets	(0.6)	1.0
Other current assets	4.1	2.2
Total current assets	77.3	64.2
Equity investments	215.1	213.5
Property, plant and equipment, net	42.6	43.1
Goodwill	152.9	149.9
Intangible assets, net	122.7	128.1
Deferred tax assets	5.1	1.1
Affiliated loan receivables	237.6	212.0
Other noncurrent assets	5.0	5.2
Total assets	858.3	817.1
LIABILITIES AND EQUITY
Accounts payable	28.1	9.0
Affiliated payables	8.2	2.7
Accrued liabilities	20.5	29.5
Short-term debt and current portion of long-term debt	0.0	0.0
Total current liabilities	56.8	41.2
Long-term debt	0.0	0.0
Affiliated debt	30.8	35.9
Other long-term liabilities	13.0	7.7
Total liabilities	100.6	84.8
Koppers shareholders' equity	757.7	732.3
Noncontrolling interests	0.0	0.0
Total liabilities and equity	858.3	817.1
Non-Guarantor Subsidiaries [Member] | Senior Notes [Member]
Assets
Cash and cash equivalents	50.4	50.2	$ 54.4	$ 52.2
Receivables, net	88.0	103.0
Affiliated receivables	18.5	1.3
Inventories, net	100.0	102.6
Deferred tax assets	4.1	1.5
Other current assets	34.4	34.6
Total current assets	295.4	293.2
Equity investments	2.4	3.6
Property, plant and equipment, net	128.9	135.4
Goodwill	59.8	57.5
Intangible assets, net	33.1	37.4
Deferred tax assets	6.6	7.7
Affiliated loan receivables	42.0	40.9
Other noncurrent assets	1.9	0.9
Total assets	570.1	576.6
LIABILITIES AND EQUITY
Accounts payable	64.9	50.6
Affiliated payables	15.1	13.5
Accrued liabilities	41.6	55.0
Short-term debt and current portion of long-term debt	15.1	13.9
Total current liabilities	136.7	133.0
Long-term debt	42.7	42.6
Affiliated debt	70.1	112.0
Other long-term liabilities	69.7	35.0
Total liabilities	319.2	322.6
Koppers shareholders' equity	242.4	240.1
Noncontrolling interests	8.5	13.9
Total liabilities and equity	$ 570.1	$ 576.6