Note 4 - Loans and the Allowance for Loan Losses - Impaired Loans (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Recorded investment with no related allowance recorded	$ 1,548,000		$ 1,705,000
Recorded investment with an allowance	535,000		539,000
Impaired Financing Receivable, Related Allowance	153,000		154,000
Recorded investment	2,083,000		2,244,000
Unpaid principal balance	2,224,000		2,399,000
Average recorded investment	2,111,000	$ 1,771,000	1,777,000
Interest income recognized	45,000	$ 45,000	62,000
Commercial Portfolio Segment [Member] \| Commercial Loans [Member]
Recorded investment with no related allowance recorded	0		25,000
Unpaid principal balance with no related allowance recorded	0		85,000
Average recorded investment with no related allowance recorded	0		23,000
Interest income recognized with no related allowance recorded	0		0
Recorded investment with an allowance	0		0
Unpaid principal balance with allowance	0		0
Impaired Financing Receivable, Related Allowance	0		0
Average recorded investment with an allowance	0		0
Interest income recognized with an allowance	0		0
Recorded investment	0		25,000
Unpaid principal balance	0		85,000
Average recorded investment	0		23,000
Interest income recognized	0		0
Commercial Portfolio Segment [Member] \| Agricultural Loans [Member]
Recorded investment with no related allowance recorded	245,000		248,000
Unpaid principal balance with no related allowance recorded	245,000		248,000
Average recorded investment with no related allowance recorded	247,000		249,000
Interest income recognized with no related allowance recorded	14,000		19,000
Recorded investment with an allowance	0		0
Unpaid principal balance with allowance	0		0
Impaired Financing Receivable, Related Allowance	0		0
Average recorded investment with an allowance	0		0
Interest income recognized with an allowance	0		0
Recorded investment	245,000		248,000
Unpaid principal balance	245,000		248,000
Average recorded investment	247,000		249,000
Interest income recognized	14,000		19,000
Commercial Portfolio Segment [Member] \| Real Estate Loan [Member]
Recorded investment with no related allowance recorded	534,000		563,000
Unpaid principal balance with no related allowance recorded	604,000		614,000
Average recorded investment with no related allowance recorded	549,000		476,000
Interest income recognized with no related allowance recorded	0		0
Recorded investment with an allowance	252,000		252,000
Unpaid principal balance with allowance	271,000		261,000
Impaired Financing Receivable, Related Allowance	122,000		121,000
Average recorded investment with an allowance	252,000		139,000
Interest income recognized with an allowance	0		0
Recorded investment	786,000		815,000
Unpaid principal balance	875,000		875,000
Average recorded investment	801,000		615,000
Interest income recognized	0		0
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Recorded investment with no related allowance recorded	0		0
Unpaid principal balance with no related allowance recorded	0		0
Average recorded investment with no related allowance recorded	0		0
Interest income recognized with no related allowance recorded	0		0
Recorded investment with an allowance	108,000		110,000
Unpaid principal balance with allowance	108,000		110,000
Impaired Financing Receivable, Related Allowance	5,000		5,000
Average recorded investment with an allowance	109,000		114,000
Interest income recognized with an allowance	5,000		7,000
Recorded investment	108,000		110,000
Unpaid principal balance	108,000		110,000
Average recorded investment	109,000		114,000
Interest income recognized	5,000		7,000
Residential Portfolio Segment [Member] \| Real Estate Loan [Member]
Recorded investment with no related allowance recorded	474,000		435,000
Unpaid principal balance with no related allowance recorded	500,000		447,000
Average recorded investment with no related allowance recorded	477,000		385,000
Interest income recognized with no related allowance recorded	21,000		29,000
Recorded investment with an allowance	175,000		177,000
Unpaid principal balance with allowance	175,000		177,000
Impaired Financing Receivable, Related Allowance	26,000		28,000
Average recorded investment with an allowance	176,000		178,000
Interest income recognized with an allowance	5,000		7,000
Recorded investment	649,000		612,000
Unpaid principal balance	675,000		624,000
Average recorded investment	653,000		563,000
Interest income recognized	26,000		36,000
Residential Portfolio Segment [Member] \| Equity Lines of Credit [Member]
Recorded investment with no related allowance recorded	295,000		434,000
Unpaid principal balance with no related allowance recorded	321,000		457,000
Average recorded investment with no related allowance recorded	301,000		213,000
Interest income recognized with no related allowance recorded	0		0
Recorded investment with an allowance	0		0
Unpaid principal balance with allowance	0		0
Impaired Financing Receivable, Related Allowance	0		0
Average recorded investment with an allowance	0		0
Interest income recognized with an allowance	0		0
Recorded investment	295,000		434,000
Unpaid principal balance	321,000		457,000
Average recorded investment	301,000		213,000
Interest income recognized	0		0
Consumer Portfolio Segment [Member] \| Automobile Loan [Member]
Recorded investment with no related allowance recorded	0		0
Unpaid principal balance with no related allowance recorded	0		0
Average recorded investment with no related allowance recorded	0		0
Interest income recognized with no related allowance recorded	0		0
Recorded investment with an allowance	0		0
Unpaid principal balance with allowance	0		0
Impaired Financing Receivable, Related Allowance	0		0
Average recorded investment with an allowance	0		0
Interest income recognized with an allowance	0		0
Recorded investment	0		0
Unpaid principal balance	0		0
Average recorded investment	0		0
Interest income recognized	0		0
Consumer Portfolio Segment [Member] \| Other Loans [Member]
Recorded investment with no related allowance recorded	0		0
Unpaid principal balance with no related allowance recorded	0		0
Average recorded investment with no related allowance recorded	0		0
Interest income recognized with no related allowance recorded	0		0
Recorded investment with an allowance	0		0
Unpaid principal balance with allowance	0		0
Impaired Financing Receivable, Related Allowance	0		0
Average recorded investment with an allowance	0		0
Interest income recognized with an allowance	0		0
Recorded investment	0		0
Unpaid principal balance	0		0
Average recorded investment	0		0
Interest income recognized	$ 0		$ 0

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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-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

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