Business and geographic segments - Net Sales by Point of Origin and Point of Destination (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Business and geographic segments
Net sales	$ 2,104.8	$ 1,921.7	$ 2,222.5
Operating Segment | Point of Origin
Business and geographic segments
Net sales	2,104.8	1,921.7	2,222.5
Operating Segment | Point of Destination
Business and geographic segments
Net sales	2,104.8	1,921.7	2,222.5
Operating Segment | United States | Point of Origin
Business and geographic segments
Net sales	1,396.1	1,284.4	1,518.9
Operating Segment | Germany | Point of Origin
Business and geographic segments
Net sales	826.6	726.4	895.4
Operating Segment | Canada | Point of Origin
Business and geographic segments
Net sales	351.5	351.0	389.4
Operating Segment | Norway | Point of Origin
Business and geographic segments
Net sales	278.6	252.1	273.5
Operating Segment | Belgium | Point of Origin
Business and geographic segments
Net sales	237.8	217.1	306.5
Operating Segment | North America | Point of Destination
Business and geographic segments
Net sales	914.0	871.0	985.4
Operating Segment | Europe | Point of Destination
Business and geographic segments
Net sales	842.2	738.5	879.0
Operating Segment | Asia and other | Point of Destination
Business and geographic segments
Net sales	348.6	312.2	358.1
Eliminations | Point of Origin
Business and geographic segments
Net sales	$ (985.8)	$ (909.3)	$ (1,161.2)