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Fair Value of Financial Instruments (Tables) | 6 Months Ended
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Jun. 30, 2017
Financial Instruments, Owned, at Fair Value [Abstract] |
Estimated Fair Values of Financial Instruments | The following table presents the estimated fair values of financial instruments:
| June 30, 2017 |  | December 31, 2016
| (Amounts in thousands)
Assets |  |  |
Investments | $ | 3,659,158 |  |  | $ | 3,547,560 |
Total return swaps | — |  |  | 667 |
Liabilities |  |  |
Total return swaps | $ | 1,725 |  |  | $ | 765 |
Options sold | 104 |  |  | 20 |
Secured notes | — |  |  | 140,000 |
Unsecured notes | 380,059 |  |  | 180,000 |

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