Financial Derivatives Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Interest Rate Swaps [Member]
Derivative [Line Items]
Average Monthly Notional Amount	$ 2,258,733	$ 2,463,892
Credit Default Swap [Member]
Derivative [Line Items]
Average Monthly Notional Amount	2,146,231	1,080,772
Total Return Swaps [Member]
Derivative [Line Items]
Average Monthly Notional Amount	89,435	112,641
Futures [Member]
Derivative [Line Items]
Average Monthly Notional Amount	634,975	880,682
Options [Member]
Derivative [Line Items]
Average Monthly Notional Amount	900,488	865,600
Forwards [Member]
Derivative [Line Items]
Average Monthly Notional Amount	96,351	107,448
Warrant [Member]
Derivative [Line Items]
Average Monthly Notional Amount	1,555	1,554
Mortgage Loan Purchase Commitments [Member]
Derivative [Line Items]
Average Monthly Notional Amount	$ 10,043	$ 2,093