Income taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Tax [Line Items]
Income tax expense	$ 131,000	$ 1,280,000
Effective income tax rate reconciliation, percent	(0.10%)	(1.00%)
Deferred tax assets, valuation allowance	$ 173,540,000	$ 145,589,000
Net valuation allowance increases	28,000,000.0	35,500,000
Federal net operating loss carryforwards	222,800,000	214,900,000
Federal net operating loss carryforwards do not expire	$ 222,800,000
Percentage of taxable income limitation under TCJA	80.00%
State net operating loss carryforwards	$ 338,300,000	315,300,000
Accrued interest or penalties related to uncertain tax benefits	0	0
IRS
Income Tax [Line Items]
Net operating loss carryforwards limited and expire due to ownership changes	0
Federal | Research tax credit carryforward
Income Tax [Line Items]
Tax credit carryforwards	15,800,000	12,600,000
State | Research tax credit carryforward
Income Tax [Line Items]
Tax credit carryforwards	$ 7,800,000	$ 5,200,000