Business Segment Information - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Net sales	$ 455.2	$ 496.5	$ 1,431.4	$ 1,383.6
Cost of sales	322.5	332.1	929.4	958.8
Gross margin	132.7	164.4	502.0	424.8
Operating income (loss)	69.2	103.1	318.0	250.3
Securities earnings	19.3	7.5	36.1	21.6
Insurance recoveries	0.5	0.1	0.9	0.2
Gain on land sales			12.5
Other components of net periodic pension and OPEB expense	(3.7)	(4.5)	(11.2)	(12.9)
Litigation expense			(62.0)
Loss on prepayment of debt		(7.1)		(7.1)
General expenses, net	(14.4)	(7.2)	(43.6)	(26.4)
Interest expense	(14.0)	(15.0)	(45.4)	(44.2)
Income from continuing operations before income taxes	56.9	76.9	205.3	181.5
Chemicals
Segment Reporting Information [Line Items]
Net sales	410.3	464.5	1,312.5	1,275.7
Cost of sales	291.7	309.9	848.3	883.7
Gross margin	118.6	154.6	464.2	392.0
Operating income (loss)	61.0	98.4	295.2	234.7
Component Products
Segment Reporting Information [Line Items]
Net sales	30.0	26.9	90.8	86.9
Cost of sales	20.4	18.8	60.5	59.6
Gross margin	9.6	8.1	30.3	27.3
Operating income (loss)	4.5	3.4	14.9	12.5
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales	14.9	5.1	28.1	21.0
Cost of sales	10.4	3.4	20.6	15.5
Gross margin	4.5	1.7	7.5	5.5
Operating income (loss)	$ 3.7	$ 1.3	$ 7.9	$ 3.1