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Summary of significant accounting policies - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Schedule Of Significant Accounting Policies [Line Items] |  |  |
Advertising costs | $ 0.5 | $ 0.5 | $ 0.4
Defined contribution plan expense | 3.5 | 3.9 | 3.9
Income tax payments to NL | $ 6.2 | $ 7.3 | $ 7.8
Minimum | Building |  |  |
Schedule Of Significant Accounting Policies [Line Items] |  |  |
Property and equipment, estimated useful lives | 15 years |  |
Minimum | Equipment and software |  |  |
Schedule Of Significant Accounting Policies [Line Items] |  |  |
Property and equipment, estimated useful lives | 3 years |  |
Maximum | Building |  |  |
Schedule Of Significant Accounting Policies [Line Items] |  |  |
Property and equipment, estimated useful lives | 40 years |  |
Maximum | Equipment and software |  |  |
Schedule Of Significant Accounting Policies [Line Items] |  |  |
Property and equipment, estimated useful lives | 20 years |  |
NL Industries | CompX International Inc |  |  |
Schedule Of Significant Accounting Policies [Line Items] |  |  |
Percentage of ownership held by parent company | 87.00% |  |
Valhi Inc | NL Industries |  |  |
Schedule Of Significant Accounting Policies [Line Items] |  |  |
Percentage of ownership held by parent company | 83.00% |  |
Contran Corporation | Valhi Inc |  |  |
Schedule Of Significant Accounting Policies [Line Items] |  |  |
Percentage of ownership held by parent company | 91.00% |  |

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