Note 10 - Income Taxes - A Reconciliation of Income Tax Expense (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Computed at statutory rate	34.00%	34.00%	34.00%
State financial institution tax and credits	(4.20%)	(4.80%)	(3.40%)
Cash surrender value of life insurance	(2.20%)	(1.50%)	(1.60%)
Tax exempt interest	(3.30%)	(1.70%)	(1.40%)
Other	2.20%	4.10%	(0.80%)
Actual effective rate	26.50%	30.10%	26.80%