Revenue - Disaggregation of Sales - Schedule of Disaggregates of Net Sales of our Chemicals Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Net sales	$ 509.0	$ 459.3
Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	465.0	421.0
Point of Origin | Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	465.0	421.0
Point of Origin | Chemicals | United States
Disaggregation Of Revenue [Line Items]
Net sales	253.9	237.0
Point of Origin | Chemicals | Germany
Disaggregation Of Revenue [Line Items]
Net sales	231.2	229.1
Point of Origin | Chemicals | Canada
Disaggregation Of Revenue [Line Items]
Net sales	97.2	67.7
Point of Origin | Chemicals | Belgium
Disaggregation Of Revenue [Line Items]
Net sales	66.5	66.1
Point of Origin | Chemicals | Norway
Disaggregation Of Revenue [Line Items]
Net sales	71.0	54.3
Point of Origin | Chemicals | Eliminations
Disaggregation Of Revenue [Line Items]
Net sales	(254.8)	(233.2)
Point of Destination | Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	465.0	421.0
Point of Destination | Chemicals | Europe
Disaggregation Of Revenue [Line Items]
Net sales	227.3	214.5
Point of Destination | Chemicals | North America
Disaggregation Of Revenue [Line Items]
Net sales	145.3	132.3
Point of Destination | Chemicals | Other
Disaggregation Of Revenue [Line Items]
Net sales	$ 92.4	$ 74.2