Financial Derivatives Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands |
6 Months Ended | 12 Months Ended |
|---|---|---|
Jun. 30, 2018 |
Dec. 31, 2017 |
|
| Interest Rate Swaps [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | $ 1,113,420 | $ 1,306,853 |
| Credit Default Swap [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 601,794 | 531,008 |
| Total Return Swaps [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 36,059 | 19,760 |
| Futures [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 101,664 | 48,244 |
| Options [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 124,741 | 94,415 |
| Forwards [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 44,541 | 76,784 |
| Warrant [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | 0 | 378 |
| Mortgage Loan Purchase Commitments [Member] | ||
| Derivative [Line Items] | ||
| Average Monthly Notional Amount | $ 0 | $ 1,585 |