Stock-Based Compensation - Schedule of Option Activity under 2009 Plan and 2019 Plan (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Shares Available for Grant
Shares Available for Grant, Beginning balance	2,689,624
Shares Available for Grant, Awards authorized	1,040,530
Shares Available for Grant, Options forfeited	15,062
Shares Available for Grant, Ending balance	3,745,216	2,689,624
Number of Shares
Number of Shares, Beginning balance	2,087,202
Number of Shares, Options exercised	(431,041)
Number of Shares, Options forfeited	(15,062)
Number of Shares, Ending balance	1,641,099	2,087,202
Number of Shares, Vested and exercisable	1,339,978
Number of Shares, Vested and expected to vest	1,641,099
Weighted-Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Beginning balance | $ / shares	$ 5.92
Weighted-Average Exercise Price Per Share, Options exercised | $ / shares	5.91
Weighted-Average Exercise Price Per Share, Options forfeited | $ / shares	9.33
Weighted-Average Exercise Price Per Share, Ending balance | $ / shares	5.88	$ 5.92
Weighted-Average Exercise Price Per Share, Vested and exercisable | $ / shares	4.88
Weighted-Average Exercise Price Per Share, Vested and expected to vest | $ / shares	$ 5.88
Weighted-Average Remaining Term
Weighted-Average Remaining Term, Balance	5 years 11 months 23 days	6 years 9 months 7 days
Weighted-Average Remaining Term, Vested and exercisable	5 years 8 months 19 days
Weighted-Average Remaining Term, Vested and expected to vest	5 years 11 months 23 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Balance | $	$ 328,212	$ 204,137
Aggregate Intrinsic Value, Vested and exercisable | $	269,338
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 328,212