Equity - Schedule of Basic and Diluted Earnings Per Share, or EPS, Based on Weighted-Average of Both Restricted and Unrestricted Class A Common Stock Outstanding (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 73,643	$ 78,165	$ 72,312	$ 60,958	$ 57,891	$ 57,722	$ 50,613	$ 51,405	$ 285,078	$ 217,631	$ 238,297
Weighted-average shares outstanding, basic and diluted									113,857,238	95,963,616	94,165,351
Per share amount, basic and diluted	$ 0.61	$ 0.67	$ 0.66	$ 0.56	$ 0.59	$ 0.61	$ 0.53	$ 0.54	$ 2.50	$ 2.27	$ 2.53