Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands |
9 Months Ended | 12 Months Ended |
|---|---|---|
Sep. 30, 2017 |
Dec. 31, 2016 |
|
| Statement of Financial Position [Abstract] | ||
| Investments at value, cost | $ 1,758,854 | $ 1,525,710 |
| Financial derivatives–assets, at fair value Net cost | 41,041 | 40,724 |
| Repurchase agreements, cost | 194,265 | 185,205 |
| Investments sold short at value, proceeds | 672,506 | 589,429 |
| Financial derivatives-liabilities, at fair value Net proceeds | 28,507 | 12,012 |
| Other secured borrowings proceeds | $ 89,646 | $ 24,086 |
| Common stock, shares authorized | 100,000,000 | 100,000,000 |
| Common stock, shares issued | 31,992,177 | 32,294,703 |
| Common stock, shares outstanding | 31,992,177 | 32,294,703 |