Note 4 - Loans - Impaired Loan Data (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Unpaid contractual principal balance with no related allowance	$ 20,682,000	$ 15,967,000	$ 19,810,000
Impaired balance with no related allowance	19,769,000	15,857,000	19,703,000
Average recorded investment with no related allowance	20,029,000	17,218,000	17,644,000
Interest income recognized with no related allowance	383,000	348,000	904,000
Interest income collected with no related allowance	456,000	356,000	949,000
Unpaid contractual principal balance with an allowance	4,245,000	5,932,000	4,770,000
Impaired balance with an allowance	4,245,000	5,932,000	4,770,000
Related allowance	1,566,000	1,474,000	1,418,000
Average recorded investment with an allowance	3,876,000	6,287,000	6,061,000
Interest income recognized with an allowance	94,000	121,000	169,000
Interest income collected with an allowance	118,000	114,000	177,000
Unpaid contractual principal balance	25,572,000	21,899,000	24,580,000
Impaired balance	24,179,000	21,789,000	24,473,000
Average recorded investment	23,960,000	23,505,000	23,705,000
Interest income recognized	477,000	469,000	1,073,000
Interest income collected	574,000	470,000	1,126,000
Financial Asset Acquired with Credit Deterioration [Member]
Related allowance		0	0
Unpaid contractual principal balance	645,000
Impaired balance	165,000	0	0
Average recorded investment	55,000
Interest income recognized
Interest income collected
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member]
Unpaid contractual principal balance with no related allowance	442,000	367,000	595,000
Impaired balance with no related allowance	442,000	367,000	595,000
Average recorded investment with no related allowance	525,000	520,000	526,000
Interest income recognized with no related allowance	15,000	5,000	21,000
Interest income collected with no related allowance	16,000	5,000	24,000
Unpaid contractual principal balance with an allowance	0	0	42,000
Impaired balance with an allowance	0	0	42,000
Related allowance		0	6,000
Average recorded investment with an allowance	14,000	0	8,000
Interest income recognized with an allowance	0	0	2,000
Interest income collected with an allowance	0	0	2,000
Unpaid contractual principal balance	510,000	367,000	637,000
Impaired balance	484,000	367,000	637,000
Average recorded investment	553,000	520,000	534,000
Interest income recognized	15,000	5,000	23,000
Interest income collected	16,000	5,000	26,000
Commercial and Agricultural Portfolio Segment [Member] | Commercial [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Unpaid contractual principal balance	68,000
Impaired balance	42,000
Average recorded investment	14,000
Interest income recognized
Interest income collected
Commercial and Agricultural Portfolio Segment [Member] | Agricultural [Member]
Unpaid contractual principal balance with no related allowance	736,000	311,000	434,000
Impaired balance with no related allowance	716,000	290,000	413,000
Average recorded investment with no related allowance	544,000	360,000	383,000
Interest income recognized with no related allowance	9,000	9,000	18,000
Interest income collected with no related allowance	21,000	12,000	25,000
Unpaid contractual principal balance with an allowance	588,000	0	0
Impaired balance with an allowance	588,000	0	0
Related allowance	588,000	0	0
Average recorded investment with an allowance	196,000	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	1,324,000	311,000	434,000
Impaired balance	1,304,000	290,000	413,000
Average recorded investment	740,000	360,000	383,000
Interest income recognized	18,000	9,000	18,000
Interest income collected	54,000	12,000	25,000
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	69,000
Real Estate Portfolio Segment [Member] | Commercial [Member]
Unpaid contractual principal balance with no related allowance	12,372,000	10,201,000	12,164,000
Impaired balance with no related allowance	11,504,000	10,201,000	12,164,000
Average recorded investment with no related allowance	12,341,000	11,092,000	11,040,000
Interest income recognized with no related allowance	291,000	235,000	582,000
Interest income collected with no related allowance	293,000	236,000	583,000
Unpaid contractual principal balance with an allowance	3,031,000	5,047,000	3,691,000
Impaired balance with an allowance	3,031,000	5,047,000	3,691,000
Related allowance	897,000	1,371,000	1,276,000
Average recorded investment with an allowance	2,902,000	5,371,000	5,121,000
Interest income recognized with an allowance	61,000	106,000	135,000
Interest income collected with an allowance	62,000	99,000	142,000
Unpaid contractual principal balance	15,403,000	15,248,000	15,855,000
Impaired balance	14,535,000	15,248,000	15,855,000
Average recorded investment	15,243,000	16,463,000	16,161,000
Interest income recognized	352,000	341,000	717,000
Interest income collected	355,000	335,000	725,000
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	104,000	16,000	132,000
Impaired balance with no related allowance	104,000	16,000	132,000
Average recorded investment with no related allowance	115,000	38,000	69,000
Interest income recognized with no related allowance	3,000	1,000	8,000
Interest income collected with no related allowance	3,000	1,000	8,000
Unpaid contractual principal balance with an allowance		482,000	399,000
Impaired balance with an allowance		482,000	399,000
Related allowance		54,000	39,000
Average recorded investment with an allowance	133,000	487,000	466,000
Interest income recognized with an allowance		2,000	0
Interest income collected with an allowance		2,000	0
Unpaid contractual principal balance	226,000	498,000	531,000
Impaired balance	173,000	498,000	531,000
Average recorded investment	271,000	525,000	535,000
Interest income recognized	3,000	3,000	8,000
Interest income collected	3,000	3,000	8,000
Real Estate Portfolio Segment [Member] | Commercial Construction [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Unpaid contractual principal balance	122,000
Impaired balance	69,000
Average recorded investment	23,000
Interest income recognized
Interest income collected
Real Estate Portfolio Segment [Member] | Residential Construction [Member]
Unpaid contractual principal balance with no related allowance	354,000		0
Impaired balance with no related allowance	354,000		0
Average recorded investment with no related allowance	118,000		0
Interest income recognized with no related allowance	4,000		0
Interest income collected with no related allowance	4,000		0
Unpaid contractual principal balance with an allowance	0	0	0
Impaired balance with an allowance	0	0	0
Related allowance		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	354,000
Impaired balance	354,000
Average recorded investment	118,000		0
Interest income recognized	4,000		0
Interest income collected	4,000		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	3,872,000	3,892,000	4,214,000
Impaired balance with no related allowance	3,849,000	3,805,000	4,130,000
Average recorded investment with no related allowance	3,979,000	4,113,000	4,067,000
Interest income recognized with no related allowance	83,000	87,000	208,000
Interest income collected with no related allowance	98,000	89,000	213,000
Unpaid contractual principal balance with an allowance	267,000	36,000	274,000
Impaired balance with an allowance	267,000	36,000	274,000
Related allowance	49,000	21,000	61,000
Average recorded investment with an allowance	270,000	60,000	98,000
Interest income recognized with an allowance	11,000	1,000	8,000
Interest income collected with an allowance	11,000	1,000	8,000
Unpaid contractual principal balance	4,162,000	3,928,000	4,488,000
Impaired balance	4,130,000	3,841,000	4,404,000
Average recorded investment	4,254,000	4,173,000	4,165,000
Interest income recognized	94,000	88,000	216,000
Interest income collected	109,000	90,000	221,000
Real Estate Portfolio Segment [Member] | Residential [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Unpaid contractual principal balance	23,000
Impaired balance	14,000
Average recorded investment	5,000
Interest income recognized
Interest income collected
Real Estate Portfolio Segment [Member] | Farmland [Member]
Unpaid contractual principal balance with no related allowance	2,670,000	980,000	2,054,000
Impaired balance with no related allowance	2,668,000	978,000	2,052,000
Average recorded investment with no related allowance	2,246,000	896,000	1,361,000
Interest income recognized with no related allowance	(25,000)	5,000	53,000
Interest income collected with no related allowance	17,000	7,000	82,000
Unpaid contractual principal balance with an allowance	359,000	367,000	364,000
Impaired balance with an allowance	359,000	367,000	364,000
Related allowance	32,000	28,000	36,000
Average recorded investment with an allowance	361,000	369,000	368,000
Interest income recognized with an allowance	13,000	12,000	24,000
Interest income collected with an allowance	12,000	12,000	25,000
Unpaid contractual principal balance	3,266,000	1,347,000	2,418,000
Impaired balance	3,067,000	1,345,000	2,416,000
Average recorded investment	2,620,000	1,265,000	1,729,000
Interest income recognized	(12,000)	17,000	77,000
Interest income collected	29,000	19,000	107,000
Real Estate Portfolio Segment [Member] | Farmland [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Unpaid contractual principal balance	237,000
Impaired balance	40,000
Average recorded investment	13,000
Interest income recognized
Interest income collected
Consumer and Other Portfolio Segment [Member] | Consumer [Member]
Unpaid contractual principal balance with no related allowance	132,000	200,000	213,000
Impaired balance with no related allowance	132,000	200,000	213,000
Average recorded investment with no related allowance	159,000	199,000	197,000
Interest income recognized with no related allowance	3,000	6,000	14,000
Interest income collected with no related allowance	4,000	6,000	14,000
Unpaid contractual principal balance with an allowance	0	0	0
Impaired balance with an allowance	0	0	0
Related allowance		0	0
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	327,000	200,000	213,000
Impaired balance	132,000	200,000	213,000
Average recorded investment	159,000	199,000	197,000
Interest income recognized	3,000	6,000	14,000
Interest income collected	4,000	6,000	14,000
Consumer and Other Portfolio Segment [Member] | Consumer [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Unpaid contractual principal balance	195,000
Impaired balance
Average recorded investment
Interest income recognized
Interest income collected
Consumer and Other Portfolio Segment [Member] | Other [Member]
Unpaid contractual principal balance with no related allowance		0	4,000
Impaired balance with no related allowance		0	4,000
Average recorded investment with no related allowance	2,000	0	1,000
Interest income recognized with no related allowance		0	0
Interest income collected with no related allowance		0	0
Unpaid contractual principal balance with an allowance		0
Impaired balance with an allowance		0
Related allowance		0	0
Average recorded investment with an allowance		0	0
Interest income recognized with an allowance		0	0
Interest income collected with an allowance		0	0
Unpaid contractual principal balance		0	4,000
Impaired balance		0	4,000
Average recorded investment	2,000	0	1,000
Interest income recognized		0	0
Interest income collected		$ 0	$ 0
Consumer and Other Portfolio Segment [Member] | Other [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Related allowance
Impaired balance