Income taxes - Schedule of Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Tax computed at the federal statutory rate	$ (25,927)	$ (22,361)
State income taxes, net of federal tax benefit	(8)	(6)
Nondeductible executive compensation	99	685
Stock-based compensation	(1,326)	1,132
Research and development and orphan drug credits	(6,205)	(3,692)
Uncertain tax positions	1,551	910
Other, net	228	(23)
Valuation allowance	28,936	23,355
Income tax expense	$ 0	$ 0