Stock option plans - Stock option activity (Details) - 2019 Equity Incentive Plan - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Number of options
Outstanding, beginning of period	480,274	229,308	188,552
Granted	123,062	96,798	58,980
Options assumed in Atrin merger		163,733
Exercised			(11,319)
Cancelled/Forfeited	(6,870)	(9,565)	(6,905)
Outstanding, end of period	596,466	480,274	229,308	188,552
Exercisable	464,086
Vested or expected to vest	596,466
Weighted average exercise price per share
Outstanding, beginning of period (in dollars per share)	$ 89.49	$ 169.00	$ 182.00
Granted (in dollars per share)	5.68	31.40	117.40
Options assumed in Atrin merger (in dollars per share)		14.21
Exercised (in dollars per share)			18.40
Cancelled/Forfeited (in dollars per share)	21.80	118.60	330.60
Outstanding, end of period (in dollars per share)	72.95	$ 89.49	$ 169.00	$ 182.00
Exercisable (in dollars per share)	91.82
Vested or expected to vest (in dollars per share)	$ 72.95
Weighted average remaining contractual term (in years)
Outstanding	6 years 2 months 12 days	6 years 9 months 18 days	6 years 7 months 6 days	6 years 9 months 18 days
Exercisable	5 years 3 months 18 days
Vested or expected to vest	6 years 2 months 12 days
Aggregate Intrinsic Value
Outstanding	$ 45,825
Vested or expected to vest	$ 45,825
Additional Disclosures
Weighted average grant date fair value of options granted	$ 4.35	$ 23.68	$ 85.82