Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Detail) - Kronos - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule Of Equity Method Investments [Line Items]
Net sales	$ 430.4	$ 369.8
Cost of sales	255.6	263.8
Income from operations	107.5	56.4
Income tax expense	29.0	11.0
Net income	$ 70.7	$ 36.8