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Fair Value Measurements - Assets Measured at Fair Value on Recurring Basis (Details) - Recurring [Member] - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
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Equity Security [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair value assets | $ 24,500 | $ 11
Equity Mutual Fund [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair value assets | 5,954 | 5,780
Warrants [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair value assets | 20,374 |
U.S. Treasury Mutual Fund [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair value assets | 9,557 | 13,282
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Security [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair value assets | 5,110 | 11
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury Mutual Fund [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair value assets | 9,557 | 13,282
Significant Other Observable Inputs (Level 2) [Member] | Equity Security [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair value assets | 19,390 |
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Fund [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair value assets | 5,954 | $ 5,780
Significant Unobservable Inputs (Level 3) [Member] | Warrants [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fair value assets | $ 20,374 |

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258 + Details
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