Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	$ 29,921	$ 16,265
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(20,436)	(14,824)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(6,035)	(1,360)
Net Amount, Derivatives, Financial Assets	3,450	81
Net Amount Recognized, Resell Agreements, Financial Assets	9,642	7,898
Gross Amounts Not Offset, Financial Instruments, Resell Agreements, Financial Assets	0	0
Gross Amounts Not Offset, Collateral, Resell Agreements, Financial Assets	(9,642)	(7,898)
Net Amount, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Total Financial Assets	39,563	24,163
Gross Amounts Not Offset, Collateral, Financial Assets	(15,677)	(9,258)
Net Amount, Financial Assets	3,450	81
Net Amount Recognized, Derivatives, Financial Liabilities	47,898	42,603
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(20,436)	(14,824)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(26,307)	(27,012)
Net Amount, Derivatives, Financial Liabilities	1,155	767
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	791,119	668,053
Gross Amounts Not Offset, Financial Instruments, Repurchase Agreements, Financial Liabilities	0	0
Gross Amounts Not Offset, Collateral, Repurchase Agreements, Financial Liabilities	(791,119)	(668,053)
Net Amount, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	839,017	710,656
Gross Amounts Not Offset, Collateral, Financial Liabilities	(817,426)	(695,065)
Net Amount, Financial Liabilities	1,155	767
Counterparty A [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	627	3,342
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(627)	(3,342)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	18,653	18,615
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(627)	(3,342)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(17,626)	(15,167)
Net Amount, Derivatives, Financial Liabilities	400	106
Counterparty B [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	17,308	8,196
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(9,506)	(8,196)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(4,925)	0
Net Amount, Derivatives, Financial Assets	2,877	0
Net Amount Recognized, Derivatives, Financial Liabilities	9,506	9,054
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(9,506)	(8,196)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	0	(613)
Net Amount, Derivatives, Financial Liabilities	0	245
Counterparty C [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	7,991	1,187
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(7,539)	(1,187)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	452	0
Net Amount Recognized, Derivatives, Financial Liabilities	7,539	10,870
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(7,539)	(1,187)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	0	(9,683)
Net Amount, Derivatives, Financial Liabilities	0	0
Other Counterparties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	3,995	3,540
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(2,764)	(2,099)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(1,110)	(1,360)
Net Amount, Derivatives, Financial Assets	121	81
Net Amount Recognized, Derivatives, Financial Liabilities	12,200	4,064
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(2,764)	(2,099)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(8,681)	(1,549)
Net Amount, Derivatives, Financial Liabilities	$ 755	$ 416

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