Senior Secured Credit Facility - Additional Information (Detail) (USD $)	12 Months Ended										1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Leverage ratio range one [Member]	Dec. 31, 2012 Leverage ratio range two [Member]	Dec. 31, 2012 Term Loan A Facility [Member]	Dec. 31, 2012 Term Loan A Facility [Member] Subsequent Event [Member] Commencement Date [Member]	Dec. 31, 2012 Term Loan B Facility [Member]	Dec. 31, 2012 Term Loan B Facility [Member] Commencement Date [Member]	Dec. 31, 2012 Term Loan B Facility [Member] End Date [Member]	Aug. 02, 2012 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]
Schedule Of Debt [Line Items]
Aggregate principal amount						$ 275,000,000		$ 250,000,000				$ 100,000,000
Revolving Credit Facility Maturity Date						Aug. 02, 2017		Aug. 02, 2019				Aug. 02, 2017
Amount drawn from Revolving Credit Facility	555,000,000										30,000,000
Letters of Credit Covered by Revolving Credit Facility											6,000,000
Available borrowing under Revolving Credit Facility												73,000,000
Outstanding letters of credit	8,300,000											7,000,000
Repayment of principal amount under Revolving Credit Facility												10,000,000
Repayment of principal amount under Revolving Credit Facility												20,000,000
Leverage ration triggering mandatory prepayments				1.5X or higher	2.5X or higher
Trigger mandatory prepayments				25.00%	50.00%
Principal payments						2,700,000	5,200,000		600,000
Principal payments commencement						Mar. 31, 2013	Mar. 31, 2015		Mar. 31, 2013	Jun. 30, 2019
Accrued interest												1,200,000
Annual interest rate on the Senior Secured Credit Facilities						3.21%			5.00%
Revolving Credit Facility matures						Aug. 02, 2017
Interest paid												8,400,000
Credit facility issuance costs	19,176,000	542,000
Deferred financing costs recorded	14,500,000
Amortization expense for loan origination fees and deferred financing cost	$ 1,771,000