Stock-based compensation - Compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 2,672	$ 2,490	$ 5,230	$ 4,809
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	1,903	1,618	3,566	3,095
Restricted stock awards and units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	724	842	1,565	1,634
Employee stock purchase plan awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	45	30	99	81
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	690	781	1,553	1,582
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 1,982	$ 1,709	$ 3,677	$ 3,227