Income taxes - Tax Credit Carryforwards (Details) $ in Millions	Dec. 31, 2023 USD ($)
Tax Credit Carryforward [Line Items]
Tax credit carryforwards, set to expire	$ 112.7
2024
Tax Credit Carryforward [Line Items]
Tax credit carryforwards, set to expire	22.5
2025
Tax Credit Carryforward [Line Items]
Tax credit carryforwards, set to expire	20.7
2026
Tax Credit Carryforward [Line Items]
Tax credit carryforwards, set to expire	33.7
2027
Tax Credit Carryforward [Line Items]
Tax credit carryforwards, set to expire	9.1
2028
Tax Credit Carryforward [Line Items]
Tax credit carryforwards, set to expire	0.3
Thereafter
Tax Credit Carryforward [Line Items]
Tax credit carryforwards, set to expire	$ 26.4