Condensed Consolidated Statement of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]
Loss from discontinued operations, net of tax benefit	$ 0.1	$ 0	$ 0.1	$ 0.2

Discontinued operation tax expense benefit of income loss from sale of discontinued operation.

No definition available.

Name:	kop_DiscontinuedOperationTaxExpenseBenefitOfIncomeLossFromSaleOfDiscontinuedOperation
Namespace Prefix:	kop_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration