Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Detail) - Kronos - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Schedule Of Equity Method Investments [Line Items]
Net sales	$ 369.8	$ 318.4
Cost of sales	266.4	278.0
Income (loss) from operations	52.3	(0.3)
Income tax expense (benefit)	11.0	(1.4)
Net income (loss)	$ 36.8	$ (3.8)