Segment reporting - Schedule of Geographical Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) segment	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	1
Revenues	$ 4.2	$ 3.6
Non-current assets	745.3		$ 737.0
Canada
Segment Reporting Information [Line Items]
Revenues	0.1	(0.5)
Non-current assets	55.6		57.0
United States
Segment Reporting Information [Line Items]
Revenues	3.6	4.1
Non-current assets	632.1		618.9
Germany
Segment Reporting Information [Line Items]
Revenues	0.5	0.0
Non-current assets	32.1		34.9
Other
Segment Reporting Information [Line Items]
Revenues	0.0	$ 0.0
Non-current assets	$ 25.5		$ 26.2