Equity - Summary of Class A Common Stock Issuances (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			9 Months Ended
	Jun. 30, 2015	May. 31, 2015	Apr. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Net proceeds				$ 1,029,535	$ 763,407
Class A Common Stock [Member]
Shares issued				34,780,443	28,175,003
Weighted Average [Member] | Class A Common Stock [Member]
Shares issued	11,500,000	280,025	23,000,000	34,780,025
Share issue price	$ 29.42	$ 29.97	$ 29.75	$ 29.64
Net proceeds	$ 337,918	$ 7,895	$ 683,722	$ 1,029,535