Stockholders' Equity - Schedule of the Details the Movement in Our Outstanding Class A Common Stock and Restricted Class A Common Stock (Detail)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Statement Of Stockholders Equity [Abstract]
Beginning balance	3,016,407	2,277,344
Issuance of class A common stock	25,875,000
Issuance of restricted class A common stock, net		36,400
Issuance of deferred stock units	3,068	3,578
Ending balance	28,894,475	2,317,322