Income taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax [Line Items]
Deferred tax assets, valuation allowance	$ 145,589,000	$ 110,120,000
Net valuation allowance increases	35,500,000	34,700,000
Federal net operating loss carryforwards	214,900,000	171,600,000
Federal net operating loss carryforwards do not expire	$ 214,900,000
Percentage of taxable income limitation under TCJA	80.00%
State net operating loss carryforwards	$ 315,300,000	273,600,000
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	12,600,000	9,100,000
State | Research tax credit carryforward
Income Tax [Line Items]
Tax credit carryforwards	$ 5,200,000	$ 2,900,000