Stock Option Plans - Activity Under Compensation Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Beginning balance (in shares)	4,310,790	4,364,377	4,308,890
Options granted (in shares)	1,010,843	848,023	629,716
Options exercised (in shares)	(1,018,779)	(873,786)	(438,578)
Options cancelled (in shares)	(65,026)	(27,824)	(135,651)
Ending balance (in shares)	4,237,828	4,310,790	4,364,377	4,308,890
Vested and exercisable (in shares)	2,392,563
Vested and expect to vest (in shares)	4,237,828
Weighted Average Exercise Price
Beginning balance (in USD per share)	$ 7.91	$ 3.79	$ 3.09
Options granted (in USD per share)	40.67	22.77	6.51
Options exercised (in USD per share)	3.42	1.77	1.50
Options cancelled (in USD per share)	23.32	8.71	1.56
Ending balance (in USD per share)	16.56	$ 7.91	$ 3.79	$ 3.09
Vested and exercisable (in USD per share)	8.48
Vested and expected to vest (in USD per share)	$ 16.56
Weighted Average Remaining Contractual Term (in Years)
Awards outstanding	7 years 4 months 17 days	7 years 3 months 7 days	7 years 4 months 9 days	7 years 9 months 21 days
Vested and exercisable	6 years 6 months 10 days
Vested and expected to vest	7 years 4 months 17 days
Aggregate Intrinsic Value (in thousands)
Awards outstanding	$ 197,407	$ 140,234	$ 33,132	$ 5,073
Vested and exercisable	130,417
Vested and expected to vest	$ 197,407
2019 Equity Incentive Plan
Shares Available for Grant
Beginning balance (in shares)	1,554,690	57,889	328,290
Authorized (in shares)	1,250,210	2,317,000	223,664
Granted/Awarded (in shares)	(1,079,883)	(848,023)	(629,716)
Canceled (in shares)	65,670	27,824	135,651
Ending balance (in shares)	1,790,687	1,554,690	57,889	328,290