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Investment in Kronos Worldwide, Inc. - Changes in Carrying Value of Investment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Balance at the beginning of the period			$ 242,374
Equity in earnings of Kronos Worldwide, Inc.	$ 7,816	$ 5,651	13,784	$ 13,858
Dividends received from Kronos			(12,678)	$ (12,678)
Equity in Kronos' other comprehensive income:
Balance at the end of the period	246,853		246,853
Kronos
Balance at the beginning of the period			242,400
Equity in earnings of Kronos Worldwide, Inc.			13,800
Dividends received from Kronos			(12,700)
Equity in Kronos' other comprehensive income:
Currency translation			1,300
Balance at the end of the period	$ 246,900		246,900
Kronos \| Defined Benefit Pension Plans
Equity in Kronos' other comprehensive income:
Defined benefit pension plans			$ 2,100