Income taxes - Schedule of components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Fixed assets and intangibles	$ 44	$ 5
Leases	348	255
Accrued expenses	5,590	4,887
Net operating loss carryforward	64,055	52,179
Stock options	2,475	3,528
R&D credit carryforward	1,886	3,431
Other	2,048	1,998
Subtotal	76,446	66,283
Less: valuation allowance	(75,858)	(65,659)
Total deferred tax assets	588	624
Deferred tax liabilities:
Leases	(339)	(243)
Prepaid expenses	(166)	(381)
Total deferred tax liabilities	(505)	(624)
Net deferred tax asset (liability)	$ 83	$ 0