Note 5 - Loans and the Allowance for Loan Losses - Impaired Loans (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Recorded investment with no related allowance recorded	$ 4,674,000		$ 1,778,000
Recorded investment with an allowance	276,000		436,000
Impaired Financing Receivable, Related Allowance	29,000		174,000
Recorded investment	4,950,000		2,214,000
Unpaid principal balance	5,094,000		2,352,000
Average recorded investment	2,610,000	$ 2,111,000	1,996,000
Interest income recognized	45,000	$ 45,000	61,000
Commercial Portfolio Segment [Member] \| Commercial 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		154,000
Unpaid principal balance with allowance	0		154,000
Impaired Financing Receivable, Related Allowance	0		143,000
Average recorded investment with an allowance	0		16,000
Interest income recognized with an allowance	0		0
Recorded investment	0		154,000
Unpaid principal balance	0		154,000
Average recorded investment	0		16,000
Interest income recognized	0		0
Commercial Portfolio Segment [Member] \| Agricultural Loans [Member]
Recorded investment with no related allowance recorded	239,000		243,000
Unpaid principal balance with no related allowance recorded	239,000		243,000
Average recorded investment with no related allowance recorded	241,000		246,000
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	239,000		243,000
Unpaid principal balance	239,000		243,000
Average recorded investment	241,000		246,000
Interest income recognized	14,000		19,000
Commercial Portfolio Segment [Member] \| Real Estate Loan [Member]
Recorded investment with no related allowance recorded	3,781,000		859,000
Unpaid principal balance with no related allowance recorded	3,874,000		955,000
Average recorded investment with no related allowance recorded	1,424,000		762,000
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	3,781,000		859,000
Unpaid principal balance	3,874,000		955,000
Average recorded investment	1,424,000		762,000
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	104,000		108,000
Unpaid principal balance with allowance	104,000		108,000
Impaired Financing Receivable, Related Allowance	5,000		5,000
Average recorded investment with an allowance	106,000		109,000
Interest income recognized with an allowance	5,000		7,000
Recorded investment	104,000		108,000
Unpaid principal balance	104,000		108,000
Average recorded investment	106,000		109,000
Interest income recognized	5,000		7,000
Residential Portfolio Segment [Member] \| Real Estate Loan [Member]
Recorded investment with no related allowance recorded	386,000		388,000
Unpaid principal balance with no related allowance recorded	399,000		399,000
Average recorded investment with no related allowance recorded	388,000		390,000
Interest income recognized with no related allowance recorded	21,000		28,000
Recorded investment with an allowance	172,000		174,000
Unpaid principal balance with allowance	172,000		176,000
Impaired Financing Receivable, Related Allowance	24,000		26,000
Average recorded investment with an allowance	173,000		175,000
Interest income recognized with an allowance	5,000		7,000
Recorded investment	558,000		562,000
Unpaid principal balance	571,000		575,000
Average recorded investment	561,000		565,000
Interest income recognized	26,000		35,000
Residential Portfolio Segment [Member] \| Equity Lines of Credit [Member]
Recorded investment with no related allowance recorded	268,000		288,000
Unpaid principal balance with no related allowance recorded	306,000		317,000
Average recorded investment with no related allowance recorded	278,000		298,000
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	268,000		288,000
Unpaid principal balance	306,000		317,000
Average recorded investment	278,000		298,000
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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