Investment in Kronos Worldwide, Inc. - Changes in Carrying Value of Investment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Balance at the beginning of the period			$ 229,543
Equity in earnings of Kronos	$ 23,645	$ 59,745	45,124	$ 70,920
Dividends received from Kronos			(11,974)	$ (10,566)
Equity in Kronos' other comprehensive income:
Balance at the end of the period	259,752		259,752
Kronos
Balance at the beginning of the period			229,500
Equity in earnings of Kronos			45,100
Dividends received from Kronos			(12,000)
Equity in Kronos' other comprehensive income:
Currency translation			(4,400)
Balance at the end of the period	$ 259,700		259,700
Kronos | Defined Benefit Pension Plans
Equity in Kronos' other comprehensive income:
Defined benefit pension plans			$ 1,500