Income taxes - Deferred taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 22,784	$ 20,523
Research and development intangibles	10,135	4,839
Research and development credits	3,782	2,878
Share-based compensation	2,533	2,016
Accrued bonus	546	383
Lease liability	350
Other	75	1
Gross deferred tax assets	40,205	30,640
Less: valuation allowance	(39,827)	(30,609)
Net deferred tax asset	378	31
Deferred tax liability
Depreciation	(46)	(31)
Right-of-use asset	(332)
Total deferred tax liabilities	$ (378)	$ (31)