Equity - Summary of Class A Common Stock Issuances (Parenthetical) (Detail) - Class A Common Stock [Member] - $ / shares	1 Months Ended			9 Months Ended
	Jun. 30, 2015	May. 31, 2015	Apr. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Shares issued				34,780,443	28,175,003
Weighted Average [Member]
Shares issued	11,500,000	280,025	23,000,000	34,780,025
Weighted average issue price		$ 29.97