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Investments in Marketable Securities - Gross Realized Gains and Losses from Sale of Available for Sale Securities (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
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Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Investments, Debt and Equity Securities [Abstract] |  |  |  |
Gross realized gains | $ 9 | $ 79 | $ 10 | $ 132
Gross realized losses | $ 0 | $ (15) | $ 0 | $ (15)

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- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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- References No definition available. + Details
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