Business and geographic segments - Net Property and Equipment by Segment (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Net property and equipment:
Net property and equipment	$ 723.4	$ 517.3	$ 523.8
United States
Net property and equipment:
Net property and equipment	302.1	40.0	45.8
Germany
Net property and equipment:
Net property and equipment	190.9	213.0	204.7
Belgium
Net property and equipment:
Net property and equipment	88.6	98.5	101.4
Norway
Net property and equipment:
Net property and equipment	73.6	83.5	83.6
Canada
Net property and equipment:
Net property and equipment	$ 68.2	$ 82.3	$ 88.3