Income taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Income Tax [Line Items]
Income tax expense	$ 121,000	$ 131,000
Effective income tax rate reconciliation, percent	(0.10%)	(0.10%)
Deferred tax assets, valuation allowance	$ 203,637,000	$ 173,540,000
Net valuation allowance increases	30,000,000.0	28,000,000.0
Federal net operating loss carryforwards	359,600,000	222,800,000
Federal net operating loss carryforwards do not expire	$ 359,600,000
Percentage of taxable income limitation under TCJA	80.00%
State net operating loss carryforwards	$ 474,900,000	338,300,000
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	18,800,000	15,800,000
State | Research tax credit carryforward
Income Tax [Line Items]
Tax credit carryforwards	$ 9,200,000	$ 7,800,000