Financial Derivatives Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Interest Rate Swaps [Member]
Derivative [Line Items]
Average Monthly Notional Amount	$ 2,585,387	$ 2,227,315
Credit Default Swap [Member]
Derivative [Line Items]
Average Monthly Notional Amount	893,705	552,411
Total Return Swaps [Member]
Derivative [Line Items]
Average Monthly Notional Amount	1,228,173	55,108
Futures [Member]
Derivative [Line Items]
Average Monthly Notional Amount	978,986	738,830
Options [Member]
Derivative [Line Items]
Average Monthly Notional Amount	820,848	926,369
Forwards [Member]
Derivative [Line Items]
Average Monthly Notional Amount	94,611	42,143
Warrant [Member]
Derivative [Line Items]
Average Monthly Notional Amount	1,554	120
Mortgage Loan Purchase Commitments [Member]
Derivative [Line Items]
Average Monthly Notional Amount	$ 840	$ 0