Revenue recognition - Disaggregation of Net Sales by Place of Manufacture and to Location of Customer (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	$ 494.4	$ 500.5	$ 984.2	$ 979.3
Point of origin
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	494.4	500.5	984.2	979.3
Point of origin \| Reportable geographical components \| United States
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	275.7	279.7	598.1	520.6
Point of origin \| Reportable geographical components \| Germany
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	214.5	216.2	431.3	428.4
Point of origin \| Reportable geographical components \| Canada
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	55.7	97.6	166.5	186.9
Point of origin \| Reportable geographical components \| Norway
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	72.8	77.7	143.3	148.7
Point of origin \| Reportable geographical components \| Belgium
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	65.6	61.0	131.3	130.6
Point of origin \| Eliminations
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	(189.9)	(231.7)	(486.3)	(435.9)
Point of destination
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	494.4	500.5	984.2	979.3
Point of destination \| Europe
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	226.8	222.6	455.3	437.5
Point of destination \| North America
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	188.2	182.5	378.4	348.5
Point of destination \| Other
Entity Wide Information Revenue From External Customer [Line Items]
Net sales	$ 79.4	$ 95.4	$ 150.5	$ 193.3