Common Stock and Stockholders' Equity (Deficit) - Stock Plan and Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shares Available for Grant
Balance, beginning of period (in shares)	1,986,390	741,971	694,280
Increase in Plan authorized shares	1,937,770	2,493,337	1,621,795
Stock options grants (in shares)	(3,910,431)	(1,522,581)	(1,574,104)
Stock options cancelled (in shares)		240,064
Stock options expired (in shares)	329,487	33,599
Balance, end of period (in shares)	343,216	1,986,390	741,971	694,280
Number of Shares Outstanding
Balance, beginning of period (in shares)	3,853,479	2,875,106	2,115,069
Stock option grants (in shares)	3,910,431	1,522,581	1,574,104
Stock option exercised (in shares)	(594,555)	(270,545)	(786,074)
Stock options cancelled (in shares)		(240,064)	(27,993)
Stock options expired (in shares)	(329,487)	(33,599)
Balance, end of period (in shares)	6,839,868	3,853,479	2,875,106	2,115,069
Vested or expected to vest at end of period (in shares)	6,199,485
Exercisable as of end of period (in shares)	1,604,209
Weighted-Average Exercise Price
Balance, beginning of period (in dollars per share)	$ 7.62	$ 3.73	$ 1.14
Stock option grants (in dollars per share)	14.58		5.53
Stock option exercised (in dollars per share)	4.29		0.96
Stock options cancelled (in dollars per share)			1.60
Stock options expired (in dollars per share)	11.62
Balance, end of period (in dollars per share)	11.70	$ 7.62	$ 3.73	$ 1.14
Vested or expected to vest at end of period (in dollars per share)	11.38
Exercisable as of end of period (in dollars per share)	$ 6.08
Weighted-average remaining contractual life in Years
Weighted-average remaining contractual life (in years)	8 years 7 months 21 days	8 years 6 months 15 days	8 years 4 months 17 days	8 years 3 months 11 days
Vested or expected to vest at end of period (in years)	8 years 6 months 18 days
Exercisable as of end of period (in years)	7 years 2 months 12 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 36,795	$ 41,894	$ 6,758	$ 4,058
Stock option grants	519
Stock options exercised	6,984
Stock options expired	1,699
Vested or expected to vest at end of period	35,426
Exercisable as of end of period	17,505
Grant-date fair value of stock options granted during the period	$ 25,900	$ 10,800	$ 4,800
Fair value assumptions
Volatility, minimum (as a percent)	44.70%	45.40%	53.30%
Volatility, maximum (as a percent)	47.80%	51.00%	53.70%
Expected life (in years)	6 years	6 years 10 months 24 days	7 years
Risk-free interest rate, minimum	1.09%	1.85%	1.92%
Risk-free interest rate, maximum	2.29%	2.06%	2.30%
Maximum
Stock-based Awards
Exercisable period (in years)	10 years
Weighted Average
Fair value assumptions
Weighted-average fair value of underlying common stock	$ 6.63	$ 7.09	$ 5.53