Note 10 - Fair Values - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Total	$ 312,424,000	$ 334,655,000
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	171,131,000	186,410,000
Collateralized Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Total	28,903,000	42,470,000
Municipal General Obligation Bonds [Member]
Debt Securities, Available-for-sale, Total	101,124,000	101,079,000
Municipal Revenue Bonds [Member]
Debt Securities, Available-for-sale, Total	10,766,000	4,196,000
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	312,424,000	334,655,000
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	311,618,000	332,605,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	806,000	2,050,000
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale, Total	171,131,000	186,410,000
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	171,131,000	186,410,000
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	28,903,000	42,470,000
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	28,903,000	42,470,000
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	101,124,000	101,079,000
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	100,318,000	99,029,000
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	806,000	2,050,000
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member]
Debt Securities, Available-for-sale, Total	10,766,000	4,196,000
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	10,766,000	4,196,000
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