Noncontrolling Interest in Subsidiaries - Schedule of Noncontrolling Interest in Net Income of Subsidiaries (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	$ 10.2	$ 18.5
Kronos Worldwide, Inc.
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	5.9	13.8
NL Industries
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	2.6	2.4
CompX International
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	0.5	0.5
BMI
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	0.5	0.6
LandWell
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	$ 0.7	$ 1.2