Stock-based compensation - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended	12 Months Ended
	Mar. 31, 2020	[1]	Sep. 30, 2021	Dec. 31, 2020
Number of Shares Underlying Outstanding Options
Number of shares underlying outstanding options, beginning balance (in shares)			25,732,503
Number of shares underlying outstanding options, options granted (in shares)			645,796
Number of shares underlying outstanding options, options exercised (in shares)	(423)		(913,279)
Number of shares underlying outstanding options, options cancelled (in shares)			(505,213)
Number of shares underlying outstanding options, ending balance (in shares)			24,959,807	25,732,503
Number of shares underlying outstanding options, vested and expected to vest (in shares)			24,959,807
Number of shares underlying outstanding options, exercisable (in shares)			8,844,727
Weighted- Average Exercise Price per Share
Weighted average exercise price, beginning balance (in dollars per share)			$ 0.39
Weighted average exercise price, options granted (in dollars per share)			10.26
Weighted average exercise price, options exercised (in dollars per share)			0.14
Weighted average exercise price, options cancelled (in dollars per share)			0.14
Weighted average exercise price, ending balance (in dollars per share)			0.67	$ 0.39
Weighted average exercise price, options vested and expected to vest (in dollars per share)			0.67
Weighted average exercise price, options exercisable (in dollars per share)			$ 0.31
Weighted- Average Remaining Contractual Term (in years)
Stock options outstanding, weighted average remaining contractual term			8 years 8 months 12 days	9 years 7 months 6 days
Stock options granted, weighted average remaining contractual term
Stock options exercised, weighted average remaining contractual term
Stock options vested and expected to vest, weighted average remaining contractual term			8 years 8 months 12 days
Stock options exercisable, weighted average remaining contractual term			8 years 1 month 6 days
Aggregate Intrinsic Value
Stock options outstanding, aggregate intrinsic value, beginning balance			$ 245,746
Stock options granted, aggregate intrinsic value
Stock options exercised, aggregate intrinsic value
Stock options outstanding, aggregate intrinsic value, ending balance			167,460	$ 245,746
Stock options vested and expected to vest, aggregate intrinsic value			167,460
Stock options exercisable, aggregate intrinsic value			$ 61,987

[1] The shares of the Company’s common and redeemable convertible preferred stock, prior to the Merger (as defined in Note 1), have been retroactively restated as shares reflecting the exchange ratio of approximately 0.703 established in the Merger as described in Note 1.