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Marketable Securities - Schedule of Marketable Securities (Detail) - USD ($) $ in Thousands | Jun. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Schedule Of Available For Sale Securities [Line Items] |  |
Market value | $ 29,141 | $ 18,206
Level 1 | Valhi Inc | Common stock |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Market value | 29,141 | 18,206
Cost basis | 24,347 | 24,347
Unrealized gain (loss) | $ 4,794 | $ (6,141)

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- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
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