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, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	$ 558.1	$ 494.4	$ 1,067.9	$ 984.2
Point of origin
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	558.1	494.4	1,067.9	984.2
Point of origin \| Reportable geographical components \| United States
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	440.7	275.7	798.4	598.1
Point of origin \| Reportable geographical components \| Germany
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	253.7	214.5	480.3	431.3
Point of origin \| Reportable geographical components \| Canada
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	87.6	55.7	175.5	166.5
Point of origin \| Reportable geographical components \| Norway
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	62.8	72.8	128.9	143.3
Point of origin \| Reportable geographical components \| Belgium
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	70.3	65.6	134.5	131.3
Point of origin \| Eliminations
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	(357.0)	(189.9)	(649.7)	(486.3)
Point of destination
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	558.1	494.4	1,067.9	984.2
Point of destination \| Europe
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	285.5	226.8	528.6	455.3
Point of destination \| North America
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	199.0	188.2	385.2	378.4
Point of destination \| Other
Entity Wide Information Revenue from External Customer [Line Items]
Net sales	$ 73.6	$ 79.4	$ 154.1	$ 150.5