Derivative Instruments Derivative Instruments (Balance Sheet Offsetting) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Derivative Asset, Amount Offset by Liabiilty	$ 0	$ 0
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	35,255	12,771
Derivative Assets	35,255	12,771
Derivative Liability, Amount Offset by Asset	0	0
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	35,006	12,729
Derivative Liabilities	35,006	12,729
Derivative Subject to Master Netting Agreement [Member]
Derivative Asset, Fair Value, Gross Asset	34,437	12,071
Derivative Asset, Amount Offset by Liabiilty	0	0
Derivative Asset, Net Amount Presented in the Balance Sheet	34,437	12,071
Derivative Asset, Not Offset, Policy Election Deduction	(31)	(94)
derivatve asset, fair value of collateral	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	34,406	11,977
Derivative Liability, Fair Value, Gross Liability	34,993	12,299
Derivative Liability, Amount Offset by Asset	0	0
Derivative Liability, Net Amount Presented in the Balance Sheet	34,993	12,299
Derivative Liability, Not Offset, Policy Election Deduction	(31)	(94)
Derivative Liability, Fair Value of Collateral	(33,218)	(10,927)
Derivative Liability, Fair Value, Amount Offset Against Collateral	1,744	1,278
Derivative Not Subject to Master Netting Agreement [Member]
Derivative Asset, Fair Value, Gross Asset	818	700
Derivative Asset, Amount Offset by Liabiilty	0	0
Derivative Asset, Not Subject to Master Netting Arrangement	818	700
Derivative Liability, Fair Value, Gross Liability	13	430
Derivative Liability, Amount Offset by Asset	0	0
Derivative Liability, Not Subject to Master Netting Arrangement	$ 13	$ 430