Note 11 - Fair Values - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Total	$ 337,876,000	$ 337,366,000
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	186,892,000	187,077,000
Collateralized Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Total	42,010,000	43,658,000
Municipal General Obligation Bonds [Member]
Debt Securities, Available-for-sale, Total	105,112,000	102,497,000
Municipal Revenue Bonds [Member]
Debt Securities, Available-for-sale, Total	3,362,000	3,634,000
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	337,876,000	337,366,000
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	334,147,000	333,637,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	3,729,000	3,729,000
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale, Total	186,892,000	187,077,000
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	186,892,000	187,077,000
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	42,010,000	43,658,000
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	42,010,000	43,658,000
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	105,112,000	102,497,000
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	101,383,000	98,768,000
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Securities, Available-for-sale, Total	3,729,000	3,729,000
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member]
Debt Securities, Available-for-sale, Total	3,362,000	3,634,000
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	3,362,000	3,634,000
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