Note 5 - Loans and the Allowance for Loan Losses - Impaired Loans (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Recorded investment with no related allowance recorded	$ 1,705,000	$ 851,000
Recorded investment with an allowance	539,000	424,000
Impaired Financing Receivable, Related Allowance	154,000	181,000	$ 82,000
Recorded investment	2,244,000	1,275,000	2,270,000
Unpaid principal balance	2,399,000	1,299,000	2,281,000
Average recorded investment	1,777,000	1,160,000	1,760,000
Interest income recognized	62,000	71,000	73,000
Commercial Portfolio Segment [Member] \| Commercial Loans [Member]
Recorded investment with no related allowance recorded	25,000
Unpaid principal balance with no related allowance recorded	85,000
Average recorded investment with no related allowance recorded	23,000
Interest income recognized with no related allowance recorded
Recorded investment with an allowance		128,000	14,000
Unpaid principal balance with allowance		128,000	14,000
Impaired Financing Receivable, Related Allowance		128,000	2,000
Average recorded investment with an allowance		1,000	15,000
Interest income recognized with an allowance			1,000
Recorded investment	25,000	128,000	14,000
Unpaid principal balance	85,000	128,000	14,000
Average recorded investment	23,000	1,000	15,000
Interest income recognized			1,000
Commercial Portfolio Segment [Member] \| Agricultural Loans [Member]
Recorded investment with no related allowance recorded	248,000	250,000	253,000
Unpaid principal balance with no related allowance recorded	248,000	250,000	253,000
Average recorded investment with no related allowance recorded	249,000	252,000	255,000
Interest income recognized with no related allowance recorded	19,000	19,000	19,000
Recorded investment with an allowance
Unpaid principal balance with allowance
Impaired Financing Receivable, Related Allowance
Average recorded investment with an allowance
Interest income recognized with an allowance
Recorded investment	248,000	250,000	253,000
Unpaid principal balance	248,000	250,000	253,000
Average recorded investment	249,000	252,000	255,000
Interest income recognized	19,000	19,000	19,000
Commercial Portfolio Segment [Member] \| Real Estate Loan [Member]
Recorded investment with no related allowance recorded	563,000	131,000	287,000
Unpaid principal balance with no related allowance recorded	614,000	144,000	287,000
Average recorded investment with no related allowance recorded	476,000	136,000	184,000
Interest income recognized with no related allowance recorded
Recorded investment with an allowance	252,000
Unpaid principal balance with allowance	261,000
Impaired Financing Receivable, Related Allowance	121,000
Average recorded investment with an allowance	139,000
Interest income recognized with an allowance
Recorded investment	815,000	131,000	287,000
Unpaid principal balance	875,000	144,000	287,000
Average recorded investment	615,000	136,000	184,000
Interest income recognized
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Recorded investment with no related allowance recorded
Unpaid principal balance with no related allowance recorded
Average recorded investment with no related allowance recorded
Interest income recognized with no related allowance recorded
Recorded investment with an allowance	110,000	117,000	224,000
Unpaid principal balance with allowance	110,000	117,000	224,000
Impaired Financing Receivable, Related Allowance	5,000	12,000	32,000
Average recorded investment with an allowance	114,000	120,000	230,000
Interest income recognized with an allowance	7,000	7,000	8,000
Recorded investment	110,000	117,000	224,000
Unpaid principal balance	110,000	117,000	224,000
Average recorded investment	114,000	120,000	230,000
Interest income recognized	7,000	7,000	8,000
Residential Portfolio Segment [Member] \| Real Estate Loan [Member]
Recorded investment with no related allowance recorded	435,000	470,000	697,000
Unpaid principal balance with no related allowance recorded	447,000	481,000	708,000
Average recorded investment with no related allowance recorded	385,000	470,000	548,000
Interest income recognized with no related allowance recorded	29,000	38,000	38,000
Recorded investment with an allowance	177,000	179,000	237,000
Unpaid principal balance with allowance	177,000	179,000	237,000
Impaired Financing Receivable, Related Allowance	28,000	41,000	48,000
Average recorded investment with an allowance	178,000	181,000	203,000
Interest income recognized with an allowance	7,000	7,000	7,000
Recorded investment	612,000	649,000	934,000
Unpaid principal balance	624,000	660,000	945,000
Average recorded investment	563,000	651,000	751,000
Interest income recognized	36,000	45,000	45,000
Residential Portfolio Segment [Member] \| Equity Lines of Credit [Member]
Recorded investment with no related allowance recorded	434,000		162,000
Unpaid principal balance with no related allowance recorded	457,000		162,000
Average recorded investment with no related allowance recorded	213,000		180,000
Interest income recognized with no related allowance recorded
Recorded investment with an allowance
Unpaid principal balance with allowance
Impaired Financing Receivable, Related Allowance
Average recorded investment with an allowance
Interest income recognized with an allowance
Recorded investment	434,000		162,000
Unpaid principal balance	457,000		162,000
Average recorded investment	213,000		180,000
Interest income recognized
Consumer Portfolio Segment [Member] \| Automobile Loan [Member]
Recorded investment with no related allowance recorded			377,000
Unpaid principal balance with no related allowance recorded			377,000
Average recorded investment with no related allowance recorded			144,000
Interest income recognized with no related allowance recorded
Recorded investment with an allowance
Unpaid principal balance with allowance
Impaired Financing Receivable, Related Allowance
Average recorded investment with an allowance
Interest income recognized with an allowance
Recorded investment			377,000
Unpaid principal balance			377,000
Average recorded investment			144,000
Interest income recognized
Consumer Portfolio Segment [Member] \| Other Loans [Member]
Recorded investment with no related allowance recorded			19,000
Unpaid principal balance with no related allowance recorded			19,000
Average recorded investment with no related allowance recorded			1,000
Interest income recognized with no related allowance recorded
Recorded investment with an allowance
Unpaid principal balance with allowance
Impaired Financing Receivable, Related Allowance
Average recorded investment with an allowance
Interest income recognized with an allowance
Recorded investment			19,000
Unpaid principal balance			19,000
Average recorded investment			1,000
Interest income recognized

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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