Revenue - Disaggregation of Sales - Schedule of Disaggregates of Net Sales of our Chemicals Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation Of Revenue [Line Items]
Net sales	$ 459.3	$ 479.6
Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	421.0	436.5
Point of Origin | Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	421.0	436.5
Point of Origin | Chemicals | Germany
Disaggregation Of Revenue [Line Items]
Net sales	229.1	219.2
Point of Origin | Chemicals | United States
Disaggregation Of Revenue [Line Items]
Net sales	237.0	245.3
Point of Origin | Chemicals | Canada
Disaggregation Of Revenue [Line Items]
Net sales	67.7	78.5
Point of Origin | Chemicals | Belgium
Disaggregation Of Revenue [Line Items]
Net sales	66.1	69.7
Point of Origin | Chemicals | Norway
Disaggregation Of Revenue [Line Items]
Net sales	54.3	51.5
Point of Origin | Chemicals | Eliminations
Disaggregation Of Revenue [Line Items]
Net sales	(233.2)	(227.7)
Point of Destination | Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	421.0	436.5
Point of Destination | Chemicals | Europe
Disaggregation Of Revenue [Line Items]
Net sales	214.5	215.2
Point of Destination | Chemicals | North America
Disaggregation Of Revenue [Line Items]
Net sales	132.3	146.8
Point of Destination | Chemicals | Other
Disaggregation Of Revenue [Line Items]
Net sales	$ 74.2	$ 74.5