Stockholders' Equity - Summary of Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, Beginning balance (in shares)	1,907,091
Options granted in period (in shares)	711,394
Options exercised in period (in shares)	(213,790)
Options forfeited in period (in shares)	(96,728)
Options outstanding, Ending balance (in shares)	2,307,967	1,907,091
Options vested and expected to vest after September 30, 2015 (in shares)	2,177,111
Exercisable options as of September 30, 2015 (in shares)	958,335
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted average exercise price, Beginning balance (in USD per share)	$ 4.16
Weighted average exercise price of options granted in period (in USD per share)	27.50
Weighted average exercise price of options exercised in period (in USD per share)	1.39
Weighted average exercise price of options forfeited in period (in USD per share)	18.61
Weighted average exercise price, Ending balance (in USD per share)	10.97	$ 4.16
Weighted average exercise price of options vested and expected to vest after September 30, 2015 (in USD per share)	10.59
Weighted average exercise price of exercisable options as of September 30, 2015 (in USD per share)	$ 2.80
Weighted average remaining contract term for outstanding options	8 years 1 month 9 days	8 years 1 month 27 days
Weighted average remaining contract term for options vested and expected to vest after September 30, 2015	8 years 21 days
Weighted average remaining contract term for exercisable options as of September 30, 2015	7 years 21 days
Aggregate intrinsic value, beginning balance	$ 50,847
Aggregate intrinsic value, ending balance	14,549	$ 50,847
Aggregate intrinsic value of options vested and expected to vest after September 30, 2015	14,094
Aggregate intrinsic value of exercisable options as of September 30, 2015	$ 9,274