Fair value measurements - Schedule of Fair Value Hierarchy of Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	$ 105.8	$ 45.7
Warrant liability	14.4	16.2
Total	14.4	16.2
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	105.8	45.7
Warrant liability	0.0	0.0
Total	0.0	0.0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	0.0	0.0
Warrant liability	0.0	0.0
Total	0.0	0.0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	0.0	0.0
Warrant liability	14.4	16.2
Total	14.4	16.2
Money market accounts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market accounts	105.8	45.7
Money market accounts | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market accounts	105.8	45.7
Money market accounts | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market accounts	0.0	0.0
Money market accounts | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market accounts	$ 0.0	$ 0.0