Assets and Liabilities Measured at Fair Value - Realized and Unrealized Gains (Losses) On Financial Instruments (Details) - USD ($) $ in Thousands  | 
12 Months Ended | ||
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Dec. 31, 2019  | 
Dec. 31, 2018  | 
Dec. 31, 2017  | 
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| Realized and Unrealized Gains (Losses) on Financial Instruments | |||
| Realized and unrealized gains (losses) on financial instruments, net | $ 1,170 | $ 3,659 | $ 3,098 | 
| Zero-strike call option | |||
| Realized and Unrealized Gains (Losses) on Financial Instruments | |||
| Realized and unrealized gains (losses) on financial instruments, net | $ 1,170 | $ 3,659 | $ 3,098 | 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Amount of realized and unrealized gain (loss) on investment. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Details 
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