Business and Geographic Segments - Net Sales by Point of Origin and Point of Destination (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 516.8	$ 458.6	$ 415.0	$ 459.3	$ 414.1	$ 475.2	$ 528.6	$ 479.6	$ 1,849.7	$ 1,897.5	$ 1,820.1
Point of Origin
Segment Reporting Information [Line Items]
Net sales									1,849.7	1,897.5	1,820.1
Point of Destination
Segment Reporting Information [Line Items]
Net sales									1,849.7	1,897.5	1,820.1
United States | Point of Origin
Segment Reporting Information [Line Items]
Net sales									1,189.8	1,164.8	997.6
Germany | Point of Origin
Segment Reporting Information [Line Items]
Net sales									836.0	883.6	886.1
Canada | Point of Origin
Segment Reporting Information [Line Items]
Net sales									319.5	328.7	307.2
Belgium | Point of Origin
Segment Reporting Information [Line Items]
Net sales									249.5	270.7	272.2
Norway | Point of Origin
Segment Reporting Information [Line Items]
Net sales									211.8	192.2	209.6
North America | Point of Destination
Segment Reporting Information [Line Items]
Net sales									778.2	740.1	698.7
Europe | Point of Destination
Segment Reporting Information [Line Items]
Net sales									783.8	824.2	817.6
Asia and other | Point of Destination
Segment Reporting Information [Line Items]
Net sales									287.7	333.2	303.8
Geography Eliminations | Point of Origin
Segment Reporting Information [Line Items]
Net sales									$ (956.9)	$ (942.5)	$ (852.6)