Business and geographic segments - Net Sales by Point of Origin and Point of Destination (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Business and geographic segments
Net sales	$ 2,077.0	$ 2,104.8	$ 1,921.7
Operating Segment \| Point of Origin
Business and geographic segments
Net sales	2,077.0	2,104.8	1,921.7
Operating Segment \| Point of Destination
Business and geographic segments
Net sales	2,077.0	2,104.8	1,921.7
Operating Segment \| United States \| Point of Origin
Business and geographic segments
Net sales	1,390.4	1,396.1	1,284.4
Operating Segment \| Germany \| Point of Origin
Business and geographic segments
Net sales	839.1	826.6	726.4
Operating Segment \| Canada \| Point of Origin
Business and geographic segments
Net sales	289.3	351.5	351.0
Operating Segment \| Norway \| Point of Origin
Business and geographic segments
Net sales	250.3	278.6	252.1
Operating Segment \| Belgium \| Point of Origin
Business and geographic segments
Net sales	236.7	237.8	217.1
Operating Segment \| North America \| Point of Destination
Business and geographic segments
Net sales	929.0	914.0	871.0
Operating Segment \| Europe \| Point of Destination
Business and geographic segments
Net sales	861.8	842.2	738.5
Operating Segment \| Asia and other \| Point of Destination
Business and geographic segments
Net sales	286.2	348.6	312.2
Eliminations \| Point of Origin
Business and geographic segments
Net sales	$ (928.8)	$ (985.8)	$ (909.3)