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Marketable Securities - Additional Information (Detail) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]    
Securities transactions loss $ (0.2)  
Valhi Inc | Common stock    
Schedule Of Available For Sale Securities [Line Items]    
Investments in publicly-traded shares 1.7 1.7
Quoted market price of per share $ 6.06 $ 6.17
Securities transactions loss $ (0.2)