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Investments - Gross Unrealized Gains and Losses and Cost of Equity (Detail) - USD ($) $ in Thousands | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Schedule Of Trading Securities And Other Trading Assets [Line Items] |  |
Equity securities, Cost | $ 33,227 | $ 24,457
Equity securities, Gross Unrealized Gains | 1,425 | 3,446
Equity securities, Gross Unrealized Losses | (1,172) |
Equity securities, Fair Value | 33,480 | 27,903
Domestic Common Stock [Member] |  |
Schedule Of Trading Securities And Other Trading Assets [Line Items] |  |
Equity securities, Cost | 33,227 | 24,457
Equity securities, Gross Unrealized Gains | 1,425 | 3,446
Equity securities, Gross Unrealized Losses | (1,172) |
Equity securities, Fair Value | $ 33,480 | $ 27,903

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