Stockholder's Equity - Additional Information (Detail) - CompX $ in Thousands	9 Months Ended
Sep. 30, 2021 USD ($) shares
Class Of Stock [Line Items]
Number of shares available for purchase under repurchase authorizations	627,547
Common Class A [Member]
Class Of Stock [Line Items]
Number of shares purchased in market transaction	50,000
Value of of shares purchased in market transaction \| $	$ 755,000

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Balance Type:	na
Period Type:	duration