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Marketable Securities - Additional Information (Detail) - Valhi Inc - Common stock - $ / shares
shares in Millions
9 Months Ended
Sep. 30, 2020
Dec. 31, 2019
Marketable Securities [Line Items]    
Investments in publicly-traded shares 144,000 144,000
Quoted market price of per share $ 13.16 $ 22.44
Reverse stock split description 1-for-12