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Organization and Basis of Presentation - Additional Information (Detail)
Jul. 17, 2018
Vote
shares
Jun. 30, 2018
Subsequent Event    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Preferred stock, shares authorized 1,000  
Preferred stock, shares issued 0  
Preferred stock, shares outstanding 0  
Common stock Conversion term The second amended and restated certificate of incorporation does not permit the reissuance or resale of any of the shares of Class B common stock which were converted, and we expect our board of directors will take action in the near term to eliminate the 10,000,000 shares of Class B common stock currently authorized by the second amended and restated certificate of incorporation.  
Subsequent Event | Class B Common Stock    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Common stock, vote per share | Vote 10  
Common stock, vote per share | Vote 1  
Common stock, shares issued 0  
Common stock, shares outstanding 0  
Common stock, shares authorized 10,000,000  
Subsequent Event | Class A Common Stock    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Common stock, vote per share | Vote 1  
Common stock, shares issued 12,435,557  
Common stock, shares outstanding 12,435,557  
Common stock, shares authorized 20,000,000  
NL Industries | Subsequent Event | Class A Common Stock    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Common stock, shares issued 10,000,000  
Common stock, shares outstanding 10,000,000  
Conversion of common stock 10,000,000  
NL Industries | CompX International Inc    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Percentage of ownership held by parent company   87.00%
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%