Income taxes - Net operating loss carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Valuation Allowance	$ 82,612	$ 117,416
Change in the valuation allowance	$ (34,800)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax computed at federal statutory tax rate	21.00%	21.00%	21.00%
State taxes, net of federal benefit	5.40%	5.20%	6.60%
Provision to return	0.90%	3.20%	4.90%
General business credit carryovers	(0.40%)	(3.50%)	3.20%
Nondeductible expenses	0.50%	(4.60%)	(3.80%)
Other	(0.40%)
Change in valuation allowance	(26.00%)	(21.30%)	(31.90%)
Total	1.00%
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 55,300
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	33,200
Investment tax credit		$ 400
Research and development tax credits carryforwards | Federal
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards	19,600
Research and development tax credits carryforwards | State
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards	$ 10,800