Marketable Securities - Classification of Marketable Securities (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2022	Dec. 31, 2021
Marketable Securities [Line Items]
Market value	$ 6.5	$ 4.2
Cost basis		3.3
Unrealized gain		0.9
Level 1 \| Common stock \| Valhi
Marketable Securities [Line Items]
Market value	6.5	4.1
Cost basis	3.2	3.2
Unrealized gain	$ 3.3	0.9
Level 1 \| Common stock \| NL And CompX
Marketable Securities [Line Items]
Market value		0.1
Cost basis		$ 0.1

Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of investment in marketable security, classified as noncurrent.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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- Definition

Amount of unrealized gain (loss) on investment in marketable security.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(7)(c))
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

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