Subsequent Events - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended		1 Months Ended
Dec. 31, 2012	Mar. 13, 2013 Subsequent Event 2013 Credit Agreement	Mar. 13, 2013 Subsequent Event 2013 Credit Agreement Term Loan	Mar. 13, 2013 Subsequent Event 2013 Credit Agreement Revolving Credit Facility	Mar. 13, 2013 Subsequent Event 2013 Credit Agreement Letter of Credit
Subsequent Event [Line Items]
Senior secured credit facility		$ 225.0	$ 75.0	$ 150.0	$ 50.0
Line of credit facility, term	5 years		5 years	5 years
Senior secured credit facility, maturity date			Mar. 13, 2018

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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