Employee benefit plans - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands		12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Shares (in thousands)
Outstanding at beginning of period (shares)		3,089
Granted (shares)		198
Exercised (shares)		0
Forfeited/Cancelled (shares)		(603)
Outstanding at end of period (shares)	3,089	2,684	3,089
Weighted-average exercise price
Outstanding at beginning of period (in dollars per share)		$ 9.37
Granted (usd per share)		3.58
Exercised (usd per share)		0
Outstanding at end of period (in dollars per share)	$ 9.37	$ 8.43	$ 9.37
Aggregate intrinsic value (in thousands)	$ 467,000	$ 0	$ 467,000
Vested and Expected to Vest (shares)		2,684
Vested and Expected to Vest - Weighted Average Exercise Price (in dollars per share)		$ 8.43
Vested and Expected to Vest- Weighted Average Remaining Contractual Term		5 years 29 days
Vested and Expected to Vest - Aggregate Intrinsic Value		$ 0
Exercisable (shares)		2,250
Exercisable - Weighted average exercise price (in dollars per share)		$ 8.92
Exercisable - Weighted Average Remaining Contractual Term		4 years 4 months 24 days
Exercisable - Aggregate intrinsic value		$ 0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price		$ 11.64
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 2.14	$ 5.05	$ 4.62
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value		$ 1,400,000	$ 1,500,000	$ 1,500,000
Weighted Average Remaining Contractual Term (in years)	5 years 3 months 18 days	5 years 29 days