Noncontrolling Interest in Subsidiaries - Schedule of Noncontrolling Interest in Net Income of Subsidiaries (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	$ 4.9	$ 11.1	$ 18.4	$ 21.3
Kronos Worldwide, Inc.
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			8.7	11.6
NL Industries
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			1.1	3.6
CompX International
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			0.9	1.2
BMI
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			3.0	2.0
LandWell
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			$ 4.7	$ 2.9