Income taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Income tax expense	$ 0.0	$ 0.0
Increase in valuation allowance	7.4	7.8
Federal operating loss	81.0
State net operating loss	81.4
Net operating loss generated not subject to expiration	64.0
Uncertain tax positions	0.0	$ 0.0
Percentage of taxable income offset from net operating loss			80.00%
Federal
Operating Loss Carryforwards [Line Items]
R&D tax credits	$ 2.7