Stock-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options Outstanding, Beginning Balance | shares	3,972,909
Number of Options, Granted | shares	2,264,138
Number of Options, Exercised | shares	(9,425)
Number of Options, Forfeited | shares	(199,146)
Number of Options Outstanding, Ending Balance | shares	6,028,476	3,972,909
Options vested and exercisable at September 30, 2021 | shares	1,063,653
Weighted Average Exercise Price, Options outstanding as of January 1, 2021 | $ / shares	$ 17.84
Weighted Average Exercise Price, Granted | $ / shares	33.09
Weighted Average Exercise Price, Exercised | $ / shares	17.00
Weighted Average Exercise Price, Forfeited | $ / shares	25.29
Weighted Average Exercise Price, Options outstanding as of September 30, 2021 | $ / shares	23.33	$ 17.84
Weighted Average Exercise Price, Options vested and exercisable at September 30, 2021 | $ / shares	$ 17.09
Weighted Average Contractual Life, Options outstanding	9 years 25 days	9 years 6 months 29 days
Weighted Average Contractual Life, Options vested and exercisable at September 30, 2021	8 years 9 months 21 days
Aggregate Intrinsic Value, Options outstanding at January 1, 2021 | $	$ 81,822
Aggregate Intrinsic Value, Exercised | $	71
Aggregate Intrinsic Value, Forfeited | $	948
Aggregate Intrinsic Value, Options outstanding at September 30, 2021 | $	31,564	$ 81,822
Aggregate Intrinsic Value, Options vested and exercisable at September 30, 2021 | $	$ 8,800