Equity - Schedule of Movement in Outstanding Shares of Class A Common Stock, Restricted Class A Common Stock and Deferred Stock Units (Detail) - shares	1 Months Ended	9 Months Ended
	May 31, 2013	Sep. 30, 2017	Sep. 30, 2016
Equity [Abstract]
Beginning balance		94,709,290	93,843,847
Issuance of class A common stock	25,875,000	971	812
Issuance of restricted class A common stock, net		286,773	209,798
Issuance of deferred stock units		20,560	20,850
Ending balance		95,017,594	94,075,307