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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net sales	$ 388.7	$ 455.2	$ 510.2	$ 466.0	$ 495.9	$ 496.5	$ 481.7	$ 405.3	$ 1,820.1	$ 1,879.4	$ 1,519.4
Point of Origin
Segment Reporting Information [Line Items]
Net sales									1,820.1	1,879.4	1,519.4
Point of Destination
Segment Reporting Information [Line Items]
Net sales									1,820.1	1,879.4	1,519.4
United States | Point of Origin
Segment Reporting Information [Line Items]
Net sales									997.6	992.3	819.3
Germany | Point of Origin
Segment Reporting Information [Line Items]
Net sales									886.1	918.6	699.8
Canada | Point of Origin
Segment Reporting Information [Line Items]
Net sales									307.2	309.2	257.7
Belgium | Point of Origin
Segment Reporting Information [Line Items]
Net sales									272.2	279.9	187.4
Norway | Point of Origin
Segment Reporting Information [Line Items]
Net sales									209.6	216.4	164.8
North America | Point of Destination
Segment Reporting Information [Line Items]
Net sales									698.7	668.3	566.8
Europe | Point of Destination
Segment Reporting Information [Line Items]
Net sales									817.6	899.2	698.2
Asia and other | Point of Destination
Segment Reporting Information [Line Items]
Net sales									303.8	311.9	254.4
Geography Eliminations | Point of Origin
Segment Reporting Information [Line Items]
Net sales									$ (852.6)	$ (837.0)	$ (609.6)