Stock Based Compensation - Employee Stock Option Activity and Related Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares outstanding, beginning balance	2,112,632
Shares, granted	1,553,581
Shares, cancelled	(206,997)
Shares, exercised	(164,394)
Shares outstanding, ending balance	3,294,822	2,112,632
Shares, options vested and expected to vest	3,288,066
Shares, options exercisable	1,423,760
Outstanding weighted-average exercise price per share, beginning balance	$ 4.47
Weighted-average exercise price per share, granted	$ 17.12
Weighted-average exercise price per share, cancelled	$ 13.40
Weighted-average exercise price per share, exercised	$ 2.41
Weighted-average exercise price per share, ending balance	$ 9.98	$ 4.47
Options vested and expected to vest	$ 9.79
Options exercisable	$ 5.34
Outstanding weighted-average remaining contractual life	8 years 29 days	8 years 1 month 13 days
Weighted-average remaining contractual term, options vested and expected to vest	7 years 11 months 5 days
Weighted-average remaining contractual term, options exercisable	7 years 1 month 10 days
Outstanding aggregate intrinsic value, ending balance	$ 17,985	$ 26,968
Aggregate intrinsic value, options vested and expected to vest	18,286
Aggregate intrinsic value, options exercisable	$ 12,974