Income Taxes - Summary of Information Related to Interest and Penalties on Uncertain Tax Positions (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Income Tax Disclosure [Abstract]
Interest expense	$ 0.1	$ 0.1
Penalties	0	0
Accrued interest payable	$ 0.7	$ 0.6

Name:	us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of estimated interest recognized in the period arising from income tax examinations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319

+ Details

Name:	us-gaap_IncomeTaxExaminationInterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of expense for penalties related to a tax position claimed or expected to be claimed in the tax return.

+ References

+ Details

Name:	us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest expense accrued for an underpayment of income taxes.

+ References

+ Details

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