Equity - Summary of Class A Common Stock Issuances (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				12 Months Ended
	Jun. 30, 2015	May 31, 2015	Apr. 30, 2015	May 31, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Shares issued				25,875,000	12,421,401	1,070	34,780,622
Net proceeds					$ 391,558	$ 27	$ 1,029,540
Class A Common Stock [Member]
Class of Stock [Line Items]
Shares issued	11,500,000	280,025	23,000,000		12,420,000		34,780,025
Share issue price					$ 31.57		$ 29.64
Net proceeds					$ 391,558		$ 1,029,535