Note 1 - Basis of Presentation and Significant Accounting Policies (Details Textual) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2017 USD ($)
Number of Operating Segments		1
Reclassification of Treasury Stock
Minimum Principal Balance of Loans for Quarterly Rating Review		500
Restructured Loans, Reserves		$ 250
Lessee, Operating Lease, Term of Contract		20 years
Accounting Standards Update 2016-02 [Member] | Subsequent Event [Member]
Operating Lease, Right-of-Use Asset			$ 915
Operating Lease, Liability, Total			$ 915
Reclassification from AOCI to Retained Earnings [Member] | Twelve Months Ended December 31, 2017 [Member]
Prior Period Reclassification Adjustment	$ 244
Accounting Standards Update 2016-15 [Member] | Twelve Months Ended December 31, 2017 [Member] | Reclassification of Non-service Components of Net Period Benefit Costs From Salaries and Employee Benefits to Other Expense [Member]
Prior Period Reclassification Adjustment	543
Accounting Standards Update 2016-15 [Member] | Twelve Months Ended December 31, 2017 [Member] | Reclassification of Proceeds from Bank Owned Life Insurance from Operating Activities to Investing Activities [Member]
Prior Period Reclassification Adjustment	2,640
Accounting Standards Update 2016-15 [Member] | Twelve Months Ended December 31, 2016 [Member] | Reclassification of Non-service Components of Net Period Benefit Costs From Salaries and Employee Benefits to Other Expense [Member]
Prior Period Reclassification Adjustment	523
Accounting Standards Update 2014-09 [Member] | Twelve Months Ended December 31, 2017 [Member] | Reclassification of Interchange Expense From Noninterest Expense to Net Against Interchange Income [Member]
Prior Period Reclassification Adjustment	1,680
Accounting Standards Update 2014-09 [Member] | Twelve Months Ended December 31, 2016 [Member] | Reclassification of Interchange Expense From Noninterest Expense to Net Against Interchange Income [Member]
Prior Period Reclassification Adjustment	$ 1,530
Furniture and Fixtures [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life		5 years
Furniture and Fixtures [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life		10 years
Equipment, Computer Hardware and Software [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life		3 years
Equipment, Computer Hardware and Software [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life		5 years
Building and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life		7 years
Building and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life		40 years
Land Improvements [Member]
Property, Plant and Equipment, Useful Life		20 years
Other Assets [Member]
Equity Securities without Readily Determinable Fair Value, Amount		$ 602		$ 823
Investment in Federal Home Loan Bank (FHLB) and Federal Reserve Bank (FRB) Stock [Member]
Investment Owned, at Cost		7,780		$ 9,900
Common Stock [Member]
Reclassification of Treasury Stock		(5,375)
Additional Paid-in Capital [Member]
Reclassification of Treasury Stock		$ (106,853)