Financial Derivatives Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands |
9 Months Ended | 12 Months Ended |
|---|---|---|
Sep. 30, 2017 |
Dec. 31, 2016 |
|
| Interest Rate Swaps [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | $ 1,270,482 | $ 1,731,368 |
| Credit Default Swap [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 489,515 | 1,586,923 |
| Total Return Swaps [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 22,536 | 113,628 |
| Futures [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 57,240 | 371,900 |
| Options [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 88,699 | 357,260 |
| Forwards [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 74,623 | 80,513 |
| Warrant [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 492 | 1,640 |
| Mortgage Loan Purchase Commitments [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | $ 2,060 | $ 6,143 |