Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
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| Marketable Securities [Abstract] | |||
| Fair value of securities owned | $ 300 | $ 14,200 | |
| Realized and unrealized net gains on marketable securities | 400 | 6,700 | $ 9,500 |
| Marketable securities sold at fair value | 14,200 | 24,600 | |
| Purchase of marketable securities | $ 0 | $ 0 | |
| X | ||||||||||
- Definition Marketable securities sold at fair value during period. No definition available.
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| X | ||||||||||
- Definition Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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- Definition Amount of cash outflow for purchase of marketable security. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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