Income Taxes - Unrecognized Tax Benefits (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Beginning Balance	$ 6.4us-gaap_UnrecognizedTaxBenefits	$ 6.4us-gaap_UnrecognizedTaxBenefits	$ 6.4us-gaap_UnrecognizedTaxBenefits
Ending Balance	$ 6.4us-gaap_UnrecognizedTaxBenefits	$ 6.4us-gaap_UnrecognizedTaxBenefits	$ 6.4us-gaap_UnrecognizedTaxBenefits

Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

-URI http://asc.fasb.org/extlink&oid=6527854

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

Name:	us-gaap_UnrecognizedTaxBenefits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant