Stock Based Compensation - Summary of Options Issued Under the Plan (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Share Based Arrangements To Obtain Goods And Services [Abstract]
Shares available for grant, Beginning Balance	1,009,150
Shares available for grant, Authorized under the plans	2,201,772
Shares available for grant, Granted under the plans	(1,842,000)
Shares available for grant, Surrendered/Cancelled	210,001
Shares available for grant, Ending Balance	1,578,923	1,009,150
Outstanding stock options
Outstanding stock options, Beginning Balance	5,338,707
Outstanding stock options, Granted under the Plans	1,842,000
Outstanding stock options, Exercised	(290,695)
Outstanding stock options, Surrendered/Cancelled	(210,001)
Outstanding stock options, Ending Balance	6,680,011	5,338,707
Outstanding stock options, Exercisable	1,628,142
Weighted-Average Exercise Price
Weighted-average exercise price, Beginning Balance	$ 14.01
Weighted-average exercise price, Granted under the Plans	60.44
Weighted-average exercise price, Exercised	3.10
Weighted-average exercise price, Surrendered/Cancelled	60.29
Weighted-average exercise price, Ending Balance	21.15	$ 14.01
Weighted-average exercise price, Exercisable	$ 3.81
Weighted-average remaining contractual life (years)
Weighted-average remaining contractual life (years)	9 years	9 years 2 months 12 days
Weighted-average remaining contractual life (years), Exercisable	8 years 3 months 18 days
Aggregate Intrinsic Value
Aggregate intrinsic value, Beginning Balance	$ 64,704,526
Aggregate intrinsic value, Ending Balance	237,459,824	$ 64,704,526
Aggregate intrinsic value, Exercisable	$ 93,093,140