Note 4 - Loans - Age Analysis of Past Due Loans and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Accruing loans past due	$ 3,996	$ 8,234
Nonaccrual loans	7,541	9,482
Current loans	768,454	764,311
Loans	779,991	782,027	$ 768,497
Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	3,996	8,234
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member]
Accruing loans past due	106	282
Nonaccrual loans	537	637
Current loans	50,725	56,491
Loans	51,368	57,410	46,693
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	106	282
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member]
Accruing loans past due	22	117
Nonaccrual loans	504	413
Current loans	14,764	16,269
Loans	15,290	16,799	16,351
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	22	117
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Commercial [Member]
Accruing loans past due	228	679
Nonaccrual loans	1,740	2,966
Current loans	371,295	369,889
Loans	373,263	373,534	354,098
Real Estate Portfolio Segment [Member] | Commercial [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	228	679
Real Estate Portfolio Segment [Member] | Commercial [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Commercial Construction [Member]
Accruing loans past due	22	88
Nonaccrual loans	40	463
Current loans	44,243	47,298
Loans	44,305	47,849	49,659
Real Estate Portfolio Segment [Member] | Commercial Construction [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	22	88
Real Estate Portfolio Segment [Member] | Commercial Construction [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Residential Construction [Member]
Accruing loans past due
Nonaccrual loans
Current loans	14,947	12,500
Loans	14,947	12,500	8,145
Real Estate Portfolio Segment [Member] | Residential Construction [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Residential Construction [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Residential [Member]
Accruing loans past due	2,546	6,882
Nonaccrual loans	2,569	2,734
Current loans	175,889	178,098
Loans	181,004	187,714	193,376
Real Estate Portfolio Segment [Member] | Residential [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	2,546	6,882
Real Estate Portfolio Segment [Member] | Residential [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due
Real Estate Portfolio Segment [Member] | Farmland [Member]
Accruing loans past due	929	76
Nonaccrual loans	2,015	2,052
Current loans	61,112	60,581
Loans	64,056	62,709	67,111
Real Estate Portfolio Segment [Member] | Farmland [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	929	76
Real Estate Portfolio Segment [Member] | Farmland [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due
Consumer and Other Portfolio Segment [Member] | Consumer [Member]
Accruing loans past due	143	110
Nonaccrual loans	133	213
Current loans	17,631	18,162
Loans	17,907	18,485	18,805
Consumer and Other Portfolio Segment [Member] | Consumer [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	143	110
Consumer and Other Portfolio Segment [Member] | Consumer [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due
Consumer and Other Portfolio Segment [Member] | Other [Member]
Accruing loans past due
Nonaccrual loans	3	4
Current loans	17,848	5,023
Loans	17,851	5,027	$ 14,259
Consumer and Other Portfolio Segment [Member] | Other [Member] | Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due
Consumer and Other Portfolio Segment [Member] | Other [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accruing loans past due