Equity - Summary of Class A Common Stock Issuances (Detail) - USD ($)	1 Months Ended	3 Months Ended
	May 31, 2013	Mar. 31, 2019	Mar. 31, 2018
Class of Stock [Line Items]
Shares issued	25,875,000	1,909,909	455
Net proceeds		$ 65,377,000
Class A Common Stock [Member]
Class of Stock [Line Items]
Shares issued		1,909,628
Gross share issue price		$ 34.63
Net share issue price		$ 34.28
Net proceeds		$ 65,389