Selected Quarterly Financial Data - Summary of Selected Unaudited Consolidated Quarterly Financial Information (Parenthetical) (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
Schedule Of Quarterly Financial Summary [Line Items]
Change in fair value of preferred stock warrants	$ 7,500	$ 8,600	$ 1,300	$ 17,443	$ 1,380
Adjustment to redemption value on redeemable convertible preferred stock	222,100	$ 140,900	$ 11,000	374,015	$ 49,849
Series B and B-1 [Member]
Schedule Of Quarterly Financial Summary [Line Items]
Redeemable convertible preferred stock dividend	5,543			5,543
Series C and D [Member]
Schedule Of Quarterly Financial Summary [Line Items]
Redeemable convertible preferred stock dividend	$ 20,366			$ 20,366