Derivative Financial Instruments Offsetting of Derivative Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Offsetting of Derivative Assets and Liabilities [Abstract]
Derivative Asset, Fair Value, Gross Asset	$ 400,486	$ 592,208
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(9,133)	(70)
Derivative Asset, Fair Value, Amount Offset Against Collateral	391,353	592,138
Derivative Liability, Fair Value, Gross Liability	(9,133)	(70)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	9,133	70
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 0	$ 0