Organization and Basis of Presentation - Additional Information (Detail)	Sep. 30, 2020
NL Industries | CompX International Inc
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of ownership held by parent company	86.00%
Valhi Inc | NL Industries
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of ownership held by parent company	83.00%
Contran Corporation | Valhi Inc
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of ownership held by parent company	92.00%