Stock-Based Compensation - Stock Options (Details) - Employee and non-employee stock options - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Stock Based Compensation
Shares available for grant, beginning balance	4,115
Additional shares authorized	2,107
Options granted (in shares)	(1,921)
Options forfeited (in shares)	531
Shares available for grant, end balance	4,832	4,115
Number of shares
Outstanding, beginning balance (in shares)	9,043
Options granted (in shares)	1,921
Options exercised (in shares)	(474)
Options forfeited (in shares)	(531)
Outstanding, end balance (in shares)	9,959	9,043
Exercisable (in shares)	5,498
Vested and expected to vest (in shares)	9,536
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 5.72
Granted (in dollars per share)	10.41
Exercised (in dollars per share)	3.87
Forfeited (in dollars per share)	10.45
Outstanding, end balance (in dollars per share)	6.46	$ 5.72
Exercisable (in dollars per share)	4.08
Vested and expected to vest (in dollars per share)	$ 6.33
Additional disclosures
Weighted average contractual term, options outstanding	7 years 3 months 7 days	7 years 6 months 18 days
Exercisable (in years)	6 years 1 month 2 days
Vested and expected to vest (in years)	7 years 2 months 16 days
Aggregate intrinsic value, options outstanding	$ 64,602	$ 55,396
Aggregate intrinsic value, options exercisable	48,763
Aggregate intrinsic value, vested and expected to vest	$ 63,102