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Investments in Marketable Securities - Gross Realized Gains and Losses from Sale of Available for Sale Securities (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract] |  |  |
Gross realized gains | $ 134 | $ 12 | $ 2
Gross realized losses | $ (47) | $ (2) | $ 0

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- Definition This item represents the gross profit 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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- 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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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
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