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Short Term Investments - Additional Information (Detail) - Trading Securities - USD ($) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Gain (Loss) on Securities [Line Items] |  |  |
Realized gains on sales of short-term investments, trading securities | $ 169,000 | $ 48,000 | $ 134,000
Unrealized holding loss on short-term investment | $ 0 | $ 0 | $ 0

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- Definition This item represents the gain realized during the period from the sale of trading securities. + References No definition available. + Details
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- Definition Amount of unrealized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 + Details
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