Income taxes - Net operating loss carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Valuation Allowance	$ 117,416	$ 107,563
Change in the valuation allowance	$ 9,800
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	5.20%	6.60%	(2.30%)
Provision to return	3.20%	4.90%
General business credit carryovers	(3.50%)	3.20%	(20.60%)
Nondeductible expenses	(4.60%)	(3.80%)	5.00%
Other			1.90%
Change in valuation allowance	(21.30%)	(31.90%)	(5.00%)
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 175,100
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	166,500
Investment tax credit	500
Research and development tax credits carryforwards | Federal
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards	24,000
Research and development tax credits carryforwards | State
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards	$ 9,600