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Investments - Gross Unrealized Gains and Losses and Cost of Equity (Detail) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Schedule Of Trading Securities And Other Trading Assets [Line Items] |  |
Equity securities, Cost | $ 40,674 | $ 35,787
Equity securities, Gross Unrealized Gains | 15,677 | 7,650
Equity securities, Fair Value | 56,351 | 43,437
Domestic Common Stock [Member] |  |
Schedule Of Trading Securities And Other Trading Assets [Line Items] |  |
Equity securities, Cost | 40,674 | 35,787
Equity securities, Gross Unrealized Gains | 15,677 | 7,650
Equity securities, Fair Value | $ 56,351 | $ 43,437

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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), classified as current. + 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=123594786&loc=SL75136599-209740 + Details
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