Income taxes - Narrative (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) jurisdiction audit	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Income Tax Examination [Line Items]
Income tax benefit	$ 0	$ 0	$ 0
Valuation allowance	239,468,000	190,588,000
Increase (decrease) in valuation allowance	48,900,000
Unrecognized tax benefits	0	0
Accrued interest or penalties related to uncertain tax position	$ 0	$ 0
Income taxes, number of state jurisdictions | jurisdiction	8
Number of federal or state audits in progress | audit	0
Federal
Income Tax Examination [Line Items]
Net operating loss carry forwards	$ 479,000,000
Net operating loss carryforwards subject to expiration	34,100,000
Net operating loss carryforwards not subject to expiration	444,800,000
Federal | Research and development
Income Tax Examination [Line Items]
Tax credit carryforwards	23,200,000
State
Income Tax Examination [Line Items]
Net operating loss carry forwards	414,800,000
State | Research and development
Income Tax Examination [Line Items]
Tax credit carryforwards	$ 6,800,000