Equity - Summary of Class A Common Stock Issuances (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	May 31, 2013	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Class of Stock [Line Items]
Shares issued	25,875,000		3,252,325	543
Net proceeds			$ 102,496	$ 16
Class A Common Stock [Member]
Class of Stock [Line Items]
Shares issued		3,251,449
Share issue price		$ 32.13
Net proceeds		$ 102,496