Stock-based Compensation - Schedule Options to Purchase Common Stock (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
Number of shares, options outstanding, beginning balance (in shares) | shares	4,224,433
Granted (in shares) | shares	7,469,300
Exercised (in shares) | shares	(901,250)
Forfeited (in shares) | shares	(274,220)
Number of shares, options outstanding, ending balance (in shares) | shares	10,518,263	4,224,433
Options exercisable (in shares) | shares	991,429
Weighted-Average Exercise Price
Beginning balance, weighted average exercise price (in USD per share) | $ / shares	$ 0.84
Weighted average exercise price, granted (in USD per share) | $ / shares	3.33
Weighted average exercise price, exercised (in USD per share) | $ / shares	0.73
Weighted average exercise price, cancelled (in USD per share) | $ / shares	2.96
Ending balance, weighted average exercise price (in USD per share) | $ / shares	2.56	$ 0.84
Weighted average exercise price, options exercisable (in USD per share) | $ / shares	$ 1.71
Additional Disclosures
Beginning balance, weighted average remaining contractual life	9 years	8 years 10 months 24 days
Weighted average remaining contractual life, options exercisable	7 years 9 months 18 days
Aggregate intrinsic value, beginning balance | $	$ 5,496
Aggregate intrinsic value, exercised | $	8,042
Aggregate intrinsic value, forfeited | $	1,146
Aggregate intrinsic value, ending balance | $	49,552	$ 5,496
Aggregate intrinsic value, options exercisable | $	$ 5,629