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Organization and basis of presentation - Additional Information (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Basis Of Presentation And Significant Accounting Policies [Line Items]
Cash dividends per share	$ 2.30	$ 0.25	$ 2.90	$ 0.75
Class A Common Stock
Basis Of Presentation And Significant Accounting Policies [Line Items]
Cash dividends per share	$ 2.00
NL Industries | CompX International Inc
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of ownership held by parent company	87.00%		87.00%
Valhi Inc | NL Industries
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of ownership held by parent company	83.00%		83.00%
Contran Corporation | Valhi Inc
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of ownership held by parent company	91.00%		91.00%

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

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