Segment reporting - Schedule of Geographical Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($) segment	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	1
Revenues	$ 8.4	$ 3.6	$ 12.6	$ 7.2
Non-current assets	795.6		795.6		$ 737.0
Canada
Segment Reporting Information [Line Items]
Revenues	0.1	1.4	0.2	0.9
Non-current assets	57.8		57.8		57.0
United States
Segment Reporting Information [Line Items]
Revenues	7.2	2.2	10.8	6.3
Non-current assets	682.7		682.7		618.9
Germany
Segment Reporting Information [Line Items]
Revenues	1.1	0.0	1.6	0.0
Non-current assets	29.6		29.6		34.9
Other
Segment Reporting Information [Line Items]
Revenues	0.0	$ 0.0	0.0	$ 0.0
Non-current assets	$ 25.5		$ 25.5		$ 26.2