Business and geographic segments - Net Property and Equipment by Segment (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Net property and equipment:
Net property and equipment	$ 751.6	$ 723.4	$ 517.3
United States
Net property and equipment:
Net property and equipment	293.3	302.1	40.0
Germany
Net property and equipment:
Net property and equipment	208.2	190.9	213.0
Belgium
Net property and equipment:
Net property and equipment	95.0	88.6	98.5
Norway
Net property and equipment:
Net property and equipment	81.5	73.6	83.5
Canada
Net property and equipment:
Net property and equipment	$ 73.6	$ 68.2	$ 82.3