Business Segment Information - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net sales	$ 510.2	$ 481.8	$ 976.2	$ 887.1
Cost of sales	326.2	338.0	606.9	626.7
Gross margin	184.0	143.8	369.3	260.4
Operating income (loss)	130.0	83.1	248.8	147.2
Securities earnings	8.5	7.1	16.8	14.1
Insurance recoveries	0.2		0.4	0.1
Gain on land sales			12.5
Other components of net periodic pension and OPEB expense	(3.8)	(4.3)	(7.5)	(8.4)
Litigation settlement expense	(62.0)		(62.0)
General expenses, net	(14.9)	(8.7)	(29.2)	(19.2)
Interest expense	(16.0)	(14.7)	(31.4)	(29.2)
Income from continuing operations before income taxes	42.0	62.5	148.4	104.6
Chemicals
Segment Reporting Information [Line Items]
Net sales	471.8	441.4	902.2	811.2
Cost of sales	300.5	309.6	556.6	573.8
Gross margin	171.3	131.8	345.6	237.4
Operating income (loss)	123.6	77.2	234.2	136.3
Component Products
Segment Reporting Information [Line Items]
Net sales	32.4	30.1	60.8	60.0
Cost of sales	21.2	20.5	40.1	40.8
Gross margin	11.2	9.6	20.7	19.2
Operating income (loss)	6.0	4.6	10.4	9.1
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales	6.0	10.3	13.2	15.9
Cost of sales	4.5	7.9	10.2	12.1
Gross margin	1.5	2.4	3.0	3.8
Operating income (loss)	$ 0.4	$ 1.3	$ 4.2	$ 1.8