Organization and Basis of Presentation - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021
Valhi Inc | Parent Company
Organization And Basis Of Presentation [Line Items]
Parent company ownership interest	50.00%
Valhi Inc | NL Industries Inc.
Organization And Basis Of Presentation [Line Items]
Ownership percentage in company	83.00%
NL Industries Inc. | Parent Company
Organization And Basis Of Presentation [Line Items]
Parent company ownership interest	30.00%
Contran
Organization And Basis Of Presentation [Line Items]
Controlling interest description	Consequently, at March 31, 2021 Ms. Simmons and the Family Trust may be deemed to control Contran, and therefore may be deemed to indirectly control the wholly-owned subsidiary of 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%