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Financial Instruments (Tables) | 12 Months Ended
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Dec. 31, 2020
Financial Instruments, Owned, at Fair Value [Abstract] |
Estimated Fair Values of Financial Instruments | The following table presents the fair values of financial instruments:
| December 31,
| 2020 |  | 2019
| (Amounts in thousands)
Assets |  |  |
Investments | $ | 4,729,270 |  |  | $ | 4,312,161 |
Note receivable | 5,725 |  |  | 5,665 |
Liabilities |  |  |
Options sold | — |  |  | 77 |
Unsecured notes | 415,253 |  |  | 394,279 |

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