Segment reporting - Schedule of Geographical Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024 USD ($) segment	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	1
Revenue	$ 8.4	$ 4.7	$ 21.0	$ 11.9
Non-current assets	788.5		788.5		$ 737.0
Canada
Segment Reporting Information [Line Items]
Revenue	0.0	0.1	0.3	1.0
Non-current assets	69.4		69.4		57.0
United States
Segment Reporting Information [Line Items]
Revenue	5.9	4.3	16.6	10.6
Non-current assets	670.1		670.1		618.9
Germany
Segment Reporting Information [Line Items]
Revenue	2.5	0.0	4.1	0.0
Non-current assets	27.8		27.8		34.9
Other
Segment Reporting Information [Line Items]
Revenue	0.0	$ 0.3	0.0	$ 0.3
Non-current assets	$ 21.2		$ 21.2		$ 26.2