Preferred Stock - Changes in Redemption Value of Convertible Preferred Stock (Detail) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Temporary Equity [Line Items]
Adjustment to redemption value	$ 222,100	$ 140,900	$ 11,000	$ 374,015	$ 49,849
Series B Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Adjustment to redemption value				46,976	6,447
Series B-1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Adjustment to redemption value				36,961	2,836
Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Adjustment to redemption value				52,832	2,449
Series D Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Adjustment to redemption value				237,246	38,117
Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Adjustment to redemption value				$ 374,015	$ 49,849