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