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Investments - Gross Unrealized Gains and Losses and Cost of Equity (Detail) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Schedule Of Trading Securities And Other Trading Assets [Line Items] |  |
Equity securities, Cost | $ 37,682 | $ 35,787
Equity securities, Gross Unrealized Gains | 13,161 | 7,650
Equity securities, Fair Value | 50,843 | 43,437
Domestic Common Stock [Member] |  |
Schedule Of Trading Securities And Other Trading Assets [Line Items] |  |
Equity securities, Cost | 37,682 | 35,787
Equity securities, Gross Unrealized Gains | 13,161 | 7,650
Equity securities, Fair Value | $ 50,843 | $ 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). + 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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