Note 11 - Fair Values - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Total	$ 434,257,000	$ 387,347,000
Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale, Total	0	0
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale, Total	266,828,000	242,141,000
Collateralized Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Total	35,808,000	24,890,000
Municipal General Obligation Bonds [Member]
Debt Securities, Available-for-sale, Total	115,537,000	107,824,000
Municipal Revenue Bonds [Member]
Debt Securities, Available-for-sale, Total	15,584,000	11,992,000
Other Debt and Equity Securities [Member]
Debt Securities, Available-for-sale, Total	500,000	500,000
Fair Value, Recurring [Member]
Debt Securities, Available-for-sale, Total	434,257,000	387,347,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale, Total	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale, Total	433,491,000	386,581,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	766,000	766,000
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale, Total	266,828,000	242,141,000
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale, Total	0	0
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale, Total	266,828,000	242,141,000
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	0	0
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Total	35,808,000	24,890,000
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale, Total	0	0
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale, Total	35,808,000	24,890,000
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	0	0
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member]
Debt Securities, Available-for-sale, Total	115,537,000	107,824,000
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale, Total	0	0
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale, Total	114,771,000	107,058,000
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	766,000	766,000
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member]
Debt Securities, Available-for-sale, Total	15,584,000	11,992,000
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale, Total	0	0
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale, Total	15,584,000	11,992,000
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	0	0
Fair Value, Recurring [Member] | Other Debt and Equity Securities [Member]
Debt Securities, Available-for-sale, Total	500,000	500,000
Fair Value, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale, Total	0	0
Fair Value, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale, Total	500,000	500,000
Fair Value, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	$ 0	$ 0