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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	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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- Definition

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+ References

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- Definition

Schedule of significant accounting policies.

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- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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