Stock-based compensation - Activity Under Stock Option Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Shares
Outstanding at beginning of period (in shares)	10,051,283
Granted (in shares)	4,017,763
Exercised (in shares)	(102,596)
Cancelled/forfeited (in shares)	(3,063,605)
Outstanding at end of period (in shares)	10,902,845	10,051,283
Exercisable, at end of period (in shares)	6,499,540
Weighted- Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 9.84
Granted (in dollars per share)	4.76
Exercised (in dollars per share)	4.25
Cancelled/forfeited (in dollars per share)	12.00
Outstanding at end of period (in dollars per share)	7.42	$ 9.84
Exercisable, at end of period (in dollars per share)	$ 8.23
Additional Disclosures
Weighted average remaining contractual term, options outstanding	6 years 9 months 18 days	7 years 2 months 12 days
Weighted average remaining contractual term, options exercisable	5 years 6 months
Aggregate intrinsic value, options outstanding	$ 1,786	$ 8,197
Aggregate intrinsic value, options exercisable	$ 711