Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands |
6 Months Ended | 12 Months Ended |
|---|---|---|
Jun. 30, 2018 |
Dec. 31, 2017 |
|
| Statement of Financial Position [Abstract] | ||
| Investments at value, cost | $ 2,631,409 | $ 2,071,754 |
| Financial derivatives–assets, at fair value Net cost | 24,510 | 31,474 |
| Repurchase agreements, cost | 214,346 | 155,109 |
| Investments sold short at value, proceeds | (880,825) | (640,202) |
| Financial derivatives-liabilities, at fair value Net proceeds | (18,294) | (27,463) |
| Other secured borrowings proceeds | (95,630) | (57,909) |
| Other secured financing, at fair value-Proceeds | $ (102,298) | $ (125,105) |
| Common stock, shares authorized | 100,000,000 | 100,000,000 |
| Common stock, shares issued | 30,149,880 | 31,335,938 |
| Common stock, shares outstanding | 30,149,880 | 31,335,938 |