Note 3 - Loans - Age Analysis of Past Due Loans and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Accruing loans past due	$ 4,171	$ 4,558
Nonaccrual loans	8,136	7,503
Current loans	767,136	753,223
Loans	779,443	765,284	$ 770,046
Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	4,170	4,558
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due	1
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member]
Accruing loans past due	376	329
Nonaccrual loans	471	598
Current loans	46,445	47,195
Loans	47,292	48,122	45,363
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	376	329
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member]
Accruing loans past due	65	111
Nonaccrual loans	423	399
Current loans	20,927	15,933
Loans	21,415	16,443	25,246
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	65	111
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Commercial [Member]
Accruing loans past due	895	919
Nonaccrual loans	2,277	2,172
Current loans	346,236	348,081
Loans	349,408	351,172	346,251
Real Estate Portfolio Segment [Member] | Commercial [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	895	919
Real Estate Portfolio Segment [Member] | Commercial [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Commercial Construction [Member]
Accruing loans past due	141	27
Nonaccrual loans	505	477
Current loans	52,924	44,710
Loans	53,570	45,214	36,533
Real Estate Portfolio Segment [Member] | Commercial Construction [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	141	27
Real Estate Portfolio Segment [Member] | Commercial Construction [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Residential Construction [Member]
Accruing loans past due		119
Nonaccrual loans
Current loans	12,897	8,464
Loans	12,897	8,583	8,905
Real Estate Portfolio Segment [Member] | Residential Construction [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due		119
Real Estate Portfolio Segment [Member] | Residential Construction [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Residential [Member]
Accruing loans past due	2,485	2,482
Nonaccrual loans	2,219	2,830
Current loans	184,449	188,737
Loans	189,153	194,049	196,332
Real Estate Portfolio Segment [Member] | Residential [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	2,485	2,482
Real Estate Portfolio Segment [Member] | Residential [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Farmland [Member]
Accruing loans past due	58	318
Nonaccrual loans	2,066	839
Current loans	67,945	66,611
Loans	70,069	67,768	71,903
Real Estate Portfolio Segment [Member] | Farmland [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	58	318
Real Estate Portfolio Segment [Member] | Farmland [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due
Consumer and Other Portfolio Segment [Member] | Consumer [Member]
Accruing loans past due	142	246
Nonaccrual loans	175	188
Current loans	18,306	18,522
Loans	18,623	18,956	18,677
Consumer and Other Portfolio Segment [Member] | Consumer [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	141	246
Consumer and Other Portfolio Segment [Member] | Consumer [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due	1
Consumer and Other Portfolio Segment [Member] | Other [Member]
Accruing loans past due	9	7
Current loans	17,007	14,970
Loans	17,016	14,977	$ 20,836
Consumer and Other Portfolio Segment [Member] | Other [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	9	7
Consumer and Other Portfolio Segment [Member] | Other [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due