Stock-based compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Stock options
Stock-based compensation expense included in total operating expenses	$ 21,136	$ 21,522	$ 18,409
Research and development
Stock options
Stock-based compensation expense included in total operating expenses	11,043	11,386	9,984
General and administrative
Stock options
Stock-based compensation expense included in total operating expenses	10,093	10,136	8,425
Stock options
Stock options
Stock-based compensation expense included in total operating expenses	14,171	15,814	14,528
Restricted stock units and other stock awards
Stock options
Stock-based compensation expense included in total operating expenses	6,184	5,175	3,522
Employee stock purchase plan
Stock options
Stock-based compensation expense included in total operating expenses	$ 781	$ 533	$ 359