Debt - Additional Information (Detail) (USD $)			1 Months Ended	9 Months Ended		9 Months Ended				9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Aug. 06, 2013 Senior Secured Revolving Credit Facility [Member]	Sep. 30, 2013 Senior Secured Revolving Credit Facility [Member]	Mar. 07, 2013 Senior Secured Revolving Credit Facility [Member]	Sep. 30, 2013 Senior Secured Revolving Credit Facility [Member] Until March 2017 [Member]	Sep. 30, 2013 Senior Secured Revolving Credit Facility [Member] March 2017 and Thereafter [Member]	Sep. 30, 2013 Senior Secured Revolving Credit Facility [Member] Maximum [Member]	Jun. 06, 2013 Senior Secured Revolving Credit Facility [Member] Temporary increase credit facility [Member]	Sep. 30, 2013 Senior Secured Revolving Credit Facility [Member] Extend repayment period [Member]
Proforma Debt Instrument [Line Items]
Credit facility amount					$ 500,000,000
Credit facility amount, maximum	500,000,000			800,000,000					1,000,000,000
Borrowings outstanding			840,000,000	238,000,000
Proceeds from initial public offering			716,000,000
Expiration of credit facility period				Mar. 07, 2015						Sep. 30, 2018
Percentage of amount borrowed based on credit facility				50.00%
Debt instrument, description of variable rate						30 day LIBOR	30 day LIBOR
Debt instrument, basis spread on variable rate						2.75%	3.125%
Debt instrument interest rate description	All borrowings under the credit facility bear interest at 30 day LIBOR plus 2.75% until March 2017, and thereafter at 30 day LIBOR plus 3.125%.
Cash and cash equivalents and borrowing capacity				15,000,000
Cash and cash equivalents	$ 158,065,000	$ 397,198,000		$ 7,500,000
Tangible net worth, minimum percentage				85.00%
Maximum leverage ratio								1
Percentage of proceeds from additional equity capital				85.00%