Marketable Securities - Additional Information (Detail) - Valhi Inc - Common stock shares in Millions		6 Months Ended
Jun. 01, 2020	Jun. 30, 2020 $ / shares shares	Dec. 31, 2019 $ / shares shares
Schedule Of Available For Sale Securities [Line Items]
Number of shares owned \| shares		1.2	1.2
Quoted marked price per share \| $ / shares		$ 10.48	$ 22.44
Reverse stock split description		1-for-12
Reverse stock split ratio	0.083

Balance held at close of period in number of shares.

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Description of the reverse stock split arrangement. Also provide the retroactive effect given by the reverse split that occurs after the balance sheet date but before the release of financial statements.

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