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, 2019	Sep. 30, 2018
Equity [Abstract]
Beginning balance		123,664,577	108,081,077
Issuance of class A common stock	25,875,000	10,535,507	11,484,414
Issuance of restricted class A common stock, net		317,339	300,921
Issuance of deferred stock units		23,428	23,730
Ending balance		134,540,851	119,890,142