Note 14 - Income Taxes - Reconciliation of Income Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Expected provision	$ 7,207	$ 7,388	$ 7,633
Expected provision, percentage	35.00%	35.00%	35.00%
Tax-exempt interest income	$ (1,817)	$ (1,801)	$ (1,914)
Tax-exempt interest income, percentage	(8.82%)	(8.53%)	(8.78%)
Nondeductible interest expense	$ 42	$ 40	$ 51
Nondeductible interest expense, percentage	0.20%	0.19%	0.23%
Dividends received deduction	$ (7)	$ (22)	$ (75)
Dividends received deduction, percentage	(0.03%)	(0.10%)	(0.34%)
Increase in cash surrender value of life insurance	$ (133)	$ (134)	$ (135)
Increase in cash surrender value of life insurance, percentage	(0.65%)	(0.63%)	(0.62%)
Employee stock option compensation	$ 8	$ 0	$ 0
Employee stock option compensation, percentage	0.04%	0.00%	0.00%
ESOP Dividends	$ (154)	$ 0	$ 0
ESOP Dividends, percentage	(0.75%)	0.00%	0.00%
Tax benefit from limited partnership investment	$ (73)	$ (76)	$ (80)
Tax benefit from limited partnership investment, percentage	(0.35%)	(0.36%)	(0.37%)
Effect of tax rate change	$ 2,159	$ 0	$ 0
Effect of tax rate change, percentage	10.49%	0.00%	0.00%
Other, net	$ (76)	$ (48)	$ (143)
Other, net, percentage	(0.37%)	(0.23%)	(0.66%)
Total provision	$ 7,156	$ 5,347	$ 5,337
Effective income tax provision, percentage	34.75%	25.33%	24.47%