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Organization and basis of presentation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2025 $ / shares
Class A Common Stock
Organization and basis of presentation:
Special cash dividends per share	$ 1
NL Industries | CompX International Inc
Organization and basis of presentation:
Percentage of ownership held by parent company	87.00%
Valhi Inc | NL Industries
Organization and basis of presentation:
Percentage of ownership held by parent company	83.00%
Contran Corporation | Valhi Inc
Organization and basis of presentation:
Percentage of ownership held by parent company	91.00%

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- Definition

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- Definition

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- Details

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