Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	$ 3,798	$ 14,543
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(3,565)	(10,825)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(64)	(2,725)
Net Amount, Derivatives, Financial Assets	169	993
Net Amount Recognized, Resell Agreements, Financial Assets	9,642	13,442
Gross Amounts Not Offset, Financial Instruments, Resell Agreements, Financial Assets	0	0
Gross Amounts Not Offset, Collateral, Resell Agreements, Financial Assets	(9,642)	(13,442)
Net Amount, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Total Financial Assets	13,440	27,985
Gross Amounts Not Offset, Collateral, Financial Assets	(9,706)	(16,167)
Net Amount, Financial Assets	169	993
Net Amount Recognized, Derivatives, Financial Liabilities	32,534	40,198
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(3,565)	(10,825)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(27,347)	(28,803)
Net Amount, Derivatives, Financial Liabilities	1,622	570
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	963,317	883,947
Gross Amounts Not Offset, Financial Instruments, Repurchase Agreements, Financial Liabilities	0	0
Gross Amounts Not Offset, Collateral, Repurchase Agreements, Financial Liabilities	(963,317)	(883,947)
Net Amount, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	995,851	924,145
Gross Amounts Not Offset, Collateral, Financial Liabilities	(990,664)	(912,750)
Net Amount, Financial Liabilities	1,622	570
Counterparty A [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	687	743
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(687)	(743)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	11,233	16,092
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(687)	(743)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(10,026)	(15,347)
Net Amount, Derivatives, Financial Liabilities	520	2
Counterparty B [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	223	6,901
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(223)	(5,795)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	(413)
Net Amount, Derivatives, Financial Assets	0	693
Net Amount Recognized, Derivatives, Financial Liabilities	6,867	5,795
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(223)	(5,795)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(6,344)	0
Net Amount, Derivatives, Financial Liabilities	300	0
Counterparty C [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	158	6,059
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(158)	(3,447)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	(2,312)
Net Amount, Derivatives, Financial Assets	0	300
Net Amount Recognized, Derivatives, Financial Liabilities	4,578	3,447
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(158)	(3,447)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(4,415)	0
Net Amount, Derivatives, Financial Liabilities	5	0
Counterparty D [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	1,820
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(1,820)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0
Net Amount, Derivatives, Financial Assets	0
Net Amount Recognized, Derivatives, Financial Liabilities	7,706	11,505
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(1,820)	(20)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(5,886)	(11,485)
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	910	840
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(677)	(840)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(64)	0
Net Amount, Derivatives, Financial Assets	169	0
Net Amount Recognized, Derivatives, Financial Liabilities	2,150	3,359
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(677)	(820)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(676)	(1,971)
Net Amount, Derivatives, Financial Liabilities	$ 797	$ 568