Stockholders’ Equity and Stock Option Plans - Summary of Stock Option Activity and Related Information (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Number of Shares Underlying Outstanding Options
Beginning balance (in shares) | shares	8,459,969
Options granted (in shares) | shares	660,466
Options exercised (in shares) | shares	(1,694,511)
Options canceled (in shares) | shares	(27,094)
Ending balance (in shares) | shares	7,398,830	8,459,969
Vested (in shares) | shares	4,822,778
Weighted-Average Exercise Price
Beginning balance (in usd per share) | $ / shares	$ 2.53
Options granted (in usd per share) | $ / shares	36.74
Options exercised (in usd per share) | $ / shares	1.96
Options canceled (in usd per share) | $ / shares	7.96
Ending balance (in usd per share) | $ / shares	5.69	$ 2.53
Vested (in usd per share) | $ / shares	$ 3.12
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual term (years)	7 years 3 days	6 years 9 months 29 days
Weighted average remaining contractual term vested (in years)	6 years 1 month 17 days
Aggregate intrinsic value, awards outstanding | $	$ 159,659	$ 215,144
Aggregate intrinsic value, vested | $	$ 113,146