Revenue Recognition - Schedule of Disaggregates of Net Sales of our Chemicals Segment (Detail) - Chemicals - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Point of Origin
Disaggregation Of Revenue [Line Items]
Total Net sales	$ 430.4	$ 369.8
Point of Origin | Eliminations
Disaggregation Of Revenue [Line Items]
Total Net sales	(195.3)	(202.8)
Point of Origin | Germany
Disaggregation Of Revenue [Line Items]
Total Net sales	234.5	183.6
Point of Origin | United States
Disaggregation Of Revenue [Line Items]
Total Net sales	196.8	205.7
Point of Origin | Canada
Disaggregation Of Revenue [Line Items]
Total Net sales	71.6	77.9
Point of Origin | Belgium
Disaggregation Of Revenue [Line Items]
Total Net sales	69.7	58.1
Point of Origin | Norway
Disaggregation Of Revenue [Line Items]
Total Net sales	53.1	47.3
Point of Destination
Disaggregation Of Revenue [Line Items]
Total Net sales	430.4	369.8
Point of Destination | Europe
Disaggregation Of Revenue [Line Items]
Total Net sales	233.9	179.7
Point of Destination | North America
Disaggregation Of Revenue [Line Items]
Total Net sales	127.0	124.0
Point of Destination | Other
Disaggregation Of Revenue [Line Items]
Total Net sales	$ 69.5	$ 66.1