Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	$ 27,849	$ 3,810
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(6,143)	(3,308)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(21,651)	(387)
Net Amount, Derivatives, Financial Assets	55	115
Net Amount Recognized, Resell Agreements, Financial Assets	11,642	9,642
Gross Amounts Not Offset, Financial Instruments, Resell Agreements, Financial Assets	0	0
Gross Amounts Not Offset, Collateral, Resell Agreements, Financial Assets	(11,642)	(9,642)
Net Amount, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Total Financial Assets	39,491	13,452
Gross Amounts Not Offset, Collateral, Financial Assets	(33,293)	(10,029)
Net Amount, Financial Assets	55	115
Net Amount Recognized, Derivatives, Financial Liabilities	11,185	27,375
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(6,143)	(3,308)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(4,621)	(22,768)
Net Amount, Derivatives, Financial Liabilities	421	1,299
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	1,360,298	1,117,199
Gross Amounts Not Offset, Financial Instruments, Repurchase Agreements, Financial Liabilities	0	0
Gross Amounts Not Offset, Collateral, Repurchase Agreements, Financial Liabilities	(1,360,298)	(1,117,199)
Net Amount, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	1,371,483	1,144,574
Gross Amounts Not Offset, Collateral, Financial Liabilities	(1,364,919)	(1,139,967)
Net Amount, Financial Liabilities	421	1,299
Counterparty A [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	598	395
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(598)	(395)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	4,293	7,397
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(598)	(395)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(3,651)	(7,002)
Net Amount, Derivatives, Financial Liabilities	44	0
Counterparty B [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	7,255	1,028
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(3,380)	(1,028)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(3,875)	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	3,380	4,466
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(3,380)	(1,028)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	0	(3,101)
Net Amount, Derivatives, Financial Liabilities	0	337
Counterparty C [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	81	55
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(81)	(55)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	326	1,520
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(81)	(55)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(245)	(1,450)
Net Amount, Derivatives, Financial Liabilities	0	15
Other Counterparties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	19,915	2,332
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(2,084)	(1,830)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(17,776)	(387)
Net Amount, Derivatives, Financial Assets	55	115
Net Amount Recognized, Derivatives, Financial Liabilities	3,186	13,992
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(2,084)	(1,830)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(725)	(11,215)
Net Amount, Derivatives, Financial Liabilities	$ 377	$ 947