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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Schedule Of Significant Accounting Policies [Line Items] |  |  |
Defined Contribution Plan, Cost Recognized | $ 3.0 | $ 2.4 | $ 2.6
Income tax payments to NL | $ 4.3 | $ 6.7 | $ 4.6
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 | 92.00% |  |

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