Stock-based compensation - Compensation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 9,344	$ 11,324	$ 14,934
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	5,938	7,438	11,387
Restricted stock awards and units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	3,215	3,551	3,110
Employee stock purchase plan awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	191	335	437
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	2,946	4,133	6,357
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 6,398	$ 7,191	$ 8,577