Debt - Additional Information (Detail) (USD $)	6 Months Ended				3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Minimum [Member] BasisPoint	Jun. 30, 2013 Maximum [Member] BasisPoint	Jun. 30, 2013 Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity					$ 770,000,000
Eurodollar Rate margin			187.5	237.5
Base rate margin			87.5	137.5
Line of credit facility, commitment fee			0.375%	0.50%
Line of credit facility, additional borrowings	125,000,000	484,000,000			125,000,000
Line of credit facility, repayments					225,000,000
Line of credit facility, outstanding					0
Line of credit facility, remaining borrowing capacity					$ 770,000,000