Marketable Securities - Additional Information (Detail) - Valhi Inc - Common stock - $ / shares shares in Millions	Mar. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Investments in publicly-traded shares	1.7	1.7
Quoted market price of per share	$ 1.03	$ 1.87

Balance held at close of period in number of shares.

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