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Marketable Securities - Additional Information (Detail) - Valhi Inc - Common stock - $ / shares shares in Millions | Sep. 30, 2021 | Dec. 31, 2020
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Marketable Securities [Line Items] |  |
Investments in publicly-traded shares | 144,000 | 144,000
Quoted market price of per share | $ 23.33 | $ 15.20

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