Organization and Basis of Presentation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018
Valhi Inc | Kronos Worldwide, Inc.
Organization And Basis Of Presentation [Line Items]
Ownership percentage in subsidiary	50.00%
Valhi Inc | NL Industries Inc.
Organization And Basis Of Presentation [Line Items]
Ownership percentage in company	83.00%
NL Industries Inc. | Kronos Worldwide, Inc.
Organization And Basis Of Presentation [Line Items]
Ownership percentage	30.00%
Contran
Organization And Basis Of Presentation [Line Items]
Controlling interest description	Consequently, Ms. Simmons and Ms. Connelly may be deemed to control Contran, Valhi, NL and us.
Contran | Valhi Inc
Organization And Basis Of Presentation [Line Items]
Ownership percentage of parent company held by related party	92.00%