Stock-Based Compensation - Summary of Stock Option Activity (Details) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock options, Outstanding, balance	11,408,000
Stock options, Granted	3,627,000
Stock options, Exercised	(1,116,000)
Stock options, Cancelled/Forfeited	(897,000)
Stock options, Outstanding, Balance	13,022,000	11,408,000
Stock options, Options vested and exercisable	5,841,000
Stock options, Options vested and expected to vest	10,930,000
Weighted-average exercise price, Outstanding, Balance	$ 4.42
Weighted-average exercise price, Granted	9.64
Weighted-average exercise price, Exercised	2.88
Weighted-average exercise price, Cancelled/Forfeited	5.79
Weighted-average exercise price, Outstanding, Balance	5.91	$ 4.42
Weighted-average exercise price, Options vested and exercisable	3.80
Weighted-average exercise price, Options vested and expected to vest	$ 5.63
Weighted-average remaining contractual life, options outstanding	8 years 1 month 6 days	8 years 2 months 12 days
Weighted-average remaining contractual life, options vested and exercisable	7 years
Weighted-average remaining contractual life, options vested and expected to vest	7 years 10 months 24 days