Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Schedule Of Equity Method Investments [Line Items]
Net sales	$ 35,924	$ 32,311
Cost of sales	24,889	21,880
Income from operations	3,972	2,534
Income tax expense (benefit)	2,505	(3,263)
Net income	13,257	1,910
Kronos
Schedule Of Equity Method Investments [Line Items]
Net sales	465,000	421,000
Cost of sales	369,300	332,900
Income from operations	34,000	43,500
Income tax expense (benefit)	6,000	8,400
Net income	$ 19,600	$ 27,000