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 $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 35,393	$ 13,065
Weighted-average shares outstanding, basic and diluted	58,576,025	37,967,365
Per share amount, basic and diluted	$ 0.60	$ 0.34