Note 3 - Loans - Age Analysis of Past Due Loans and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Accruing loans past due	$ 4,670	$ 4,558
Nonaccrual loans	5,632	7,503
Current loans	756,494	753,223
Loans	766,796	765,284	$ 775,566
Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	4,670	4,558
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member]
Accruing loans past due	280	329
Nonaccrual loans	367	598
Current loans	44,382	47,195
Loans	45,029	48,122	44,883
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	280	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	177	111
Nonaccrual loans	290	399
Current loans	19,570	15,933
Loans	20,037	16,443	21,810
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	177	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	1,382	919
Nonaccrual loans	1,228	2,172
Current loans	349,453	348,081
Loans	352,063	351,172	355,801
Real Estate Portfolio Segment [Member] | Commercial [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	1,382	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	354	27
Nonaccrual loans	428	477
Current loans	48,127	44,710
Loans	48,909	45,214	35,151
Real Estate Portfolio Segment [Member] | Commercial Construction [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	354	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	11,541	8,464
Loans	11,541	8,583	9,230
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	2,286	2,482
Nonaccrual loans	2,140	2,830
Current loans	183,165	188,737
Loans	187,591	194,049	200,572
Real Estate Portfolio Segment [Member] | Residential [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	2,286	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	79	318
Nonaccrual loans	979	839
Current loans	66,809	66,611
Loans	67,867	67,768	70,194
Real Estate Portfolio Segment [Member] | Farmland [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	79	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	112	246
Nonaccrual loans	200	188
Current loans	18,434	18,522
Loans	18,746	18,956	19,134
Consumer and Other Portfolio Segment [Member] | Consumer [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	112	246
Consumer and Other Portfolio Segment [Member] | Consumer [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due
Consumer and Other Portfolio Segment [Member] | Other [Member]
Accruing loans past due		7
Current loans	15,013	14,970
Loans	15,013	14,977	$ 18,791
Consumer and Other Portfolio Segment [Member] | Other [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due		7
Consumer and Other Portfolio Segment [Member] | Other [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due