Derivative Instruments Derivative Instruments (Balance Sheet Offsetting) (Details) - USD ($) $ in Thousands	Mar. 31, 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	27,568	12,771
Derivative Assets	27,568	12,771
Derivative Liability, Amount Offset by Asset	0	0
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	27,195	12,729
Derivative Liabilities	27,195	12,729
Derivative Subject to Master Netting Agreement [Member]
Derivative Asset, Fair Value, Gross Asset	26,788	12,071
Derivative Asset, Amount Offset by Liabiilty	0	0
Derivative Asset, Net Amount Presented in the Balance Sheet	26,788	12,071
Derivative Asset, Not Offset, Policy Election Deduction	(44)	(94)
derivatve asset, fair value of collateral	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	26,744	11,977
Derivative Liability, Fair Value, Gross Liability	27,143	12,299
Derivative Liability, Amount Offset by Asset	0	0
Derivative Liability, Net Amount Presented in the Balance Sheet	27,143	12,299
Derivative Liability, Not Offset, Policy Election Deduction	(44)	(94)
Derivative Liability, Fair Value of Collateral	(25,633)	(10,927)
Derivative Liability, Fair Value, Amount Offset Against Collateral	1,466	1,278
Derivative Not Subject to Master Netting Agreement [Member]
Derivative Asset, Fair Value, Gross Asset	780	700
Derivative Asset, Amount Offset by Liabiilty	0	0
Derivative Asset, Not Subject to Master Netting Arrangement	780	700
Derivative Liability, Fair Value, Gross Liability	52	430
Derivative Liability, Amount Offset by Asset	0	0
Derivative Liability, Not Subject to Master Netting Arrangement	$ 52	$ 430