Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Detail) - Kronos - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule Of Equity Method Investments [Line Items]
Net sales	$ 464.5	$ 356.1	$ 1,275.7	$ 1,030.6
Cost of sales	312.3	280.6	890.3	859.2
Income from operations	91.6	28.0	214.0	38.2
Income tax expense (benefit)	6.1	0.7	(114.0)	3.2
Net income	$ 73.8	$ 22.2	$ 307.1	$ 20.1