Equity - Summary of Class A Common Stock Issuances (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2013	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Shares issued	25,875,000	14,568,431	12,421,401	1,070
Net proceeds		$ 476,420	$ 391,558	$ 27
Class A Common Stock [Member]
Class of Stock [Line Items]
Shares issued		14,566,743
Gross share issue price		$ 33.16
Net share issue price		$ 32.76
Net proceeds		$ 476,420
Class A Common Stock [Member] | ATM Agreements [Member]
Class of Stock [Line Items]
Shares issued		7,666,743	12,420,000
Gross share issue price			$ 31.90
Net share issue price			$ 31.57
Net proceeds			$ 391,558