Business Acquisitions - Summary of Company's Revenue And Net Income From Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Business Combination Increase Decrease To Reflect Liabilities Acquired At Fair Value [Abstract]
Revenue	$ 1,819.6	$ 1,864.1
(Loss) income from continuing operations attributable to Koppers	$ (13.0)	$ 41.5

The pro forma income from continuing operations before changes in accounting and extraordinary items, net of tax effect, for the period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

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Period Type:	duration