Noncontrolling interest in Subsidiaries - Schedule of Noncontrolling Interest in Net Income of Subsidiaries (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	$ 18.5	$ 9.1
Kronos Worldwide, Inc.
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	13.8	7.2
NL Industries
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	2.4	1.4
CompX International
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	0.5	0.4
BMI
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	0.6
LandWell
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	$ 1.2	$ 0.1