Equity Incentive Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Shares
Options outstanding as of January 1, 2018	10,727,125
Options granted	2,547,028
Options exercised	(1,131,716)
Options cancelled	(637,173)
Options expired	(138,160)
Options outstanding as of September 30, 2018	11,367,104	10,727,125
Options exercisable as of September 30, 2018	6,597,314
Weighted Average Exercise Price
Options outstanding as of January 1, 2018	$ 9.94
Options granted	19.50
Options exercised	8.14
Options cancelled	14.10
Options expired	11.15
Options outstanding as of September 30, 2018	12.02	$ 9.94
Options exercisable as of September 30, 2018	$ 8.58
Weighted Average Remaining Contractual Life (Years)
Options outstanding	6 years 11 months 19 days	7 years
Options exercisable as of September 30, 2018	5 years 7 months 20 days
Aggregate Intrinsic Value
Options outstanding	$ 260,474	$ 71,430
Options exercisable as of September 30, 2018	$ 173,829