Note 4 - Loans - Impaired Loan Data (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Unpaid contractual principal balance with no related allowance	$ 17,149,000	$ 16,972,000	$ 19,810,000
Impaired balance with no related allowance	17,000,000	16,863,000	19,703,000
Average recorded investment with no related allowance	19,272,000	17,130,000	17,644,000
Interest income recognized with no related allowance	497,000	571,000	904,000
Interest income collected with no related allowance	572,000	621,000	949,000
Unpaid contractual principal balance with an allowance	4,564,000	6,672,000	4,770,000
Impaired balance with an allowance	4,569,000	6,672,000	4,770,000
Related allowance	1,639,000	1,487,000	1,418,000
Average recorded investment with an allowance	4,049,000	6,383,000	6,061,000
Interest income recognized with an allowance	149,000	208,000	169,000
Interest income collected with an allowance	172,000	210,000	177,000
Unpaid contractual principal balance	22,353,000	23,644,000	24,580,000
Impaired balance	21,724,000	23,535,000	24,473,000
Average recorded investment	23,401,000	23,513,000	23,705,000
Interest income recognized	648,000	779,000	1,073,000
Interest income collected	746,000	831,000	1,126,000
Related allowance	1,647,000
Financial Asset Acquired with Credit Deterioration [Member]
Related allowance	8,000	0	0
Unpaid contractual principal balance	640,000
Impaired balance	155,000	0	0
Average recorded investment	80,000
Interest income recognized	2,000
Interest income collected	2,000
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member]
Unpaid contractual principal balance with no related allowance	460,000	472,000	595,000
Impaired balance with no related allowance	459,000	472,000	595,000
Average recorded investment with no related allowance	508,000	508,000	526,000
Interest income recognized with no related allowance	29,000	13,000	21,000
Interest income collected with no related allowance	30,000	15,000	24,000
Unpaid contractual principal balance with an allowance	398,000	0	42,000
Impaired balance with an allowance	403,000	0	42,000
Related allowance	152,000	0	6,000
Average recorded investment with an allowance	111,000	0	8,000
Interest income recognized with an allowance	8,000	0	2,000
Interest income collected with an allowance	8,000	0	2,000
Unpaid contractual principal balance	925,000	472,000	637,000
Impaired balance	901,000	472,000	637,000
Average recorded investment	639,000	508,000	534,000
Interest income recognized	37,000	13,000	23,000
Interest income collected	38,000	15,000	26,000
Related allowance	152,000
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance	0
Unpaid contractual principal balance	67,000
Impaired balance	39,000
Average recorded investment	20,000
Interest income recognized	0
Interest income collected	0
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member]
Unpaid contractual principal balance with no related allowance	648,000	444,000	434,000
Impaired balance with no related allowance	628,000	423,000	413,000
Average recorded investment with no related allowance	565,000	375,000	383,000
Interest income recognized with no related allowance	9,000	14,000	18,000
Interest income collected with no related allowance	20,000	21,000	25,000
Unpaid contractual principal balance with an allowance	587,000	0	0
Impaired balance with an allowance	587,000	0	0
Related allowance	586,000	0	0
Average recorded investment with an allowance	294,000	0	0
Interest income recognized with an allowance	9,000	0	0
Interest income collected with an allowance	33,000	0	0
Unpaid contractual principal balance	1,235,000	444,000	434,000
Impaired balance	1,215,000	423,000	413,000
Average recorded investment	859,000	375,000	383,000
Interest income recognized	18,000	14,000	18,000
Interest income collected	53,000	21,000	25,000
Related allowance	586,000
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Impaired balance
Real Estate Portfolio Segment [Member]
Interest income collected with an allowance		0
Real Estate Portfolio Segment [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Impaired balance	66,000
Real Estate Portfolio Segment [Member] | Commercial [Member]
Unpaid contractual principal balance with no related allowance	9,300,000	9,758,000	12,164,000
Impaired balance with no related allowance	9,300,000	9,758,000	12,164,000
Average recorded investment with no related allowance	11,581,000	10,759,000	11,040,000
Interest income recognized with no related allowance	346,000	345,000	582,000
Interest income collected with no related allowance	352,000	352,000	583,000
Unpaid contractual principal balance with an allowance	2,956,000	5,800,000	3,691,000
Impaired balance with an allowance	2,956,000	5,800,000	3,691,000
Related allowance	823,000	1,394,000	1,276,000
Average recorded investment with an allowance	2,916,000	5,478,000	5,121,000
Interest income recognized with an allowance	95,000	185,000	135,000
Interest income collected with an allowance	95,000	187,000	142,000
Unpaid contractual principal balance	12,256,000	15,558,000	15,855,000
Impaired balance	12,256,000	15,558,000	15,855,000
Average recorded investment	14,497,000	16,237,000	16,161,000
Interest income recognized	441,000	530,000	717,000
Interest income collected	447,000	539,000	725,000
Related allowance	823,000
Real Estate Portfolio Segment [Member] | Commercial [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Impaired balance
Real Estate Portfolio Segment [Member] | Commercial Construction [Member]
Unpaid contractual principal balance with no related allowance	77,000	102,000	132,000
Impaired balance with no related allowance	77,000	102,000	132,000
Average recorded investment with no related allowance	105,000	54,000	69,000
Interest income recognized with no related allowance	3,000	3,000	8,000
Interest income collected with no related allowance	3,000	3,000	8,000
Unpaid contractual principal balance with an allowance	0	471,000	399,000
Impaired balance with an allowance	0	471,000	399,000
Related allowance	0	44,000	39,000
Average recorded investment with an allowance	100,000	483,000	466,000
Interest income recognized with an allowance	0	3,000	0
Interest income collected with an allowance	0	3,000	0
Unpaid contractual principal balance	197,000	573,000	531,000
Impaired balance	143,000	573,000	531,000
Average recorded investment	239,000	537,000	535,000
Interest income recognized	4,000	6,000	8,000
Interest income collected	4,000	6,000	8,000
Related allowance	0
Real Estate Portfolio Segment [Member] | Commercial Construction [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance	0
Unpaid contractual principal balance	120,000
Impaired balance	66,000
Average recorded investment	34,000
Interest income recognized	1,000
Interest income collected	1,000
Real Estate Portfolio Segment [Member] | Residential Construction [Member]
Unpaid contractual principal balance with no related allowance	0		0
Impaired balance with no related allowance	0		0
Average recorded investment with no related allowance	89,000		0
Interest income recognized with no related allowance			0
Interest income collected with no related allowance	0		0
Unpaid contractual principal balance with an allowance	0	0	0
Impaired balance with an allowance	0	0	0
Related allowance	0	0	0
Average recorded investment with an allowance	0	0	0
Interest income recognized with an allowance	0	0	0
Interest income collected with an allowance	0		0
Unpaid contractual principal balance	0		0
Impaired balance	0		0
Average recorded investment	89,000		0
Interest income recognized	0		0
Interest income collected	0		0
Related allowance	0
Real Estate Portfolio Segment [Member] | Residential Construction [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Impaired balance
Real Estate Portfolio Segment [Member] | Residential [Member]
Unpaid contractual principal balance with no related allowance	3,908,000	3,954,000	4,214,000
Impaired balance with no related allowance	3,817,000	3,868,000	4,130,000
Average recorded investment with no related allowance	3,939,000	4,052,000	4,067,000
Interest income recognized with no related allowance	129,000	141,000	208,000
Interest income collected with no related allowance	148,000	145,000	213,000
Unpaid contractual principal balance with an allowance	266,000	35,000	274,000
Impaired balance with an allowance	266,000	35,000	274,000
Related allowance	48,000	20,000	61,000
Average recorded investment with an allowance	268,000	54,000	98,000
Interest income recognized with an allowance	17,000	2,000	8,000
Interest income collected with an allowance	17,000	2,000	8,000
Unpaid contractual principal balance	4,195,000	3,989,000	4,488,000
Impaired balance	4,096,000	3,903,000	4,404,000
Average recorded investment	4,214,000	4,106,000	4,165,000
Interest income recognized	146,000	143,000	216,000
Interest income collected	165,000	147,000	221,000
Related allowance	56,000
Real Estate Portfolio Segment [Member] | Residential [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance	8,000
Unpaid contractual principal balance	21,000
Impaired balance	13,000
Average recorded investment	7,000
Interest income recognized	0
Interest income collected	0
Real Estate Portfolio Segment [Member] | Farmland [Member]
Unpaid contractual principal balance with no related allowance	2,593,000	2,067,000	2,054,000
Impaired balance with no related allowance	2,591,000	2,065,000	2,052,000
Average recorded investment with no related allowance	2,332,000	1,189,000	1,361,000
Interest income recognized with no related allowance	(23,000)	46,000	53,000
Interest income collected with no related allowance	14,000	75,000	82,000
Unpaid contractual principal balance with an allowance	357,000	366,000	364,000
Impaired balance with an allowance	357,000	366,000	364,000
Related allowance	30,000	29,000	36,000
Average recorded investment with an allowance	360,000	368,000	368,000
Interest income recognized with an allowance	20,000	18,000	24,000
Interest income collected with an allowance	19,000	18,000	25,000
Unpaid contractual principal balance	3,187,000	2,433,000	2,418,000
Impaired balance	2,985,000	2,431,000	2,416,000
Average recorded investment	2,711,000	1,557,000	1,729,000
Interest income recognized	(2,000)	64,000	77,000
Interest income collected	34,000	93,000	107,000
Related allowance	30,000
Real Estate Portfolio Segment [Member] | Farmland [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance	0
Unpaid contractual principal balance	237,000
Impaired balance	37,000
Average recorded investment	19,000
Interest income recognized	1,000
Interest income collected	1,000
Consumer and Other Portfolio Segment [Member] | Consumer [Member]
Unpaid contractual principal balance with no related allowance	163,000	175,000	213,000
Impaired balance with no related allowance	128,000	175,000	213,000
Average recorded investment with no related allowance	151,000	193,000	197,000
Interest income recognized with no related allowance	4,000	9,000	14,000
Interest income collected with no related allowance	5,000	10,000	14,000
Unpaid contractual principal balance with an allowance	0	0	0
Impaired balance with an allowance	0	0	0
Related allowance	0	0	0
Average recorded investment with an allowance	0	0	0
Interest income recognized with an allowance	0	0	0
Interest income collected with an allowance	0	0	0
Unpaid contractual principal balance	358,000	175,000	213,000
Impaired balance	128,000	175,000	213,000
Average recorded investment	151,000	193,000	197,000
Interest income recognized	4,000	9,000	14,000
Interest income collected	5,000	10,000	14,000
Related allowance	0
Consumer and Other Portfolio Segment [Member] | Consumer [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance	0
Unpaid contractual principal balance	195,000
Impaired balance	0
Average recorded investment	0
Interest income recognized	0
Interest income collected	0
Consumer and Other Portfolio Segment [Member] | Other [Member]
Unpaid contractual principal balance with no related allowance	0	0	4,000
Impaired balance with no related allowance	0	0	4,000
Average recorded investment with no related allowance	2,000	0	1,000
Interest income recognized with no related allowance	0	0	0
Interest income collected with no related allowance	0	0	0
Unpaid contractual principal balance with an allowance	0	0
Impaired balance with an allowance	0	0
Related allowance	0	0	0
Average recorded investment with an allowance	0	0	0
Interest income recognized with an allowance	0	0	0
Interest income collected with an allowance	0	0	0
Unpaid contractual principal balance		0	4,000
Impaired balance	0	0	4,000
Average recorded investment	2,000	0	1,000
Interest income recognized	0	0	0
Interest income collected	0	$ 0	$ 0
Related allowance	0
Consumer and Other Portfolio Segment [Member] | Other [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Impaired balance