Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands |
3 Months Ended | 12 Months Ended |
|---|---|---|
Mar. 31, 2019 |
Dec. 31, 2018 |
|
| Interest rate swaps | ||
| Derivative [Line Items] | ||
| Average Monthly Notional | $ 912,934 | $ 1,059,756 |
| TBAs | ||
| Derivative [Line Items] | ||
| Average Monthly Notional | 984,292 | |
| Credit default swaps | ||
| Derivative [Line Items] | ||
| Average Monthly Notional | 403,254 | 566,805 |
| Total return swaps | ||
| Derivative [Line Items] | ||
| Average Monthly Notional | 38,400 | 53,603 |
| Futures | ||
| Derivative [Line Items] | ||
| Average Monthly Notional | 280,947 | 201,295 |
| Options | ||
| Derivative [Line Items] | ||
| Average Monthly Notional | 51,545 | 99,891 |
| Forwards | ||
| Derivative [Line Items] | ||
| Average Monthly Notional | 29,078 | $ 45,522 |
| Warrants | ||
| Derivative [Line Items] | ||
| Average Monthly Notional | $ 2,281 |