Note 4 - Loans and the Allowance for Loan Losses - Impaired Loans (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Commercial Portfolio Segment [Member] \| Commercial Loans [Member]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			$ 47,000
Unpaid principal balance with no related allowance recorded			47,000
Average recorded investment with no related allowance recorded			39,000
Interest income recognized with no related allowance recorded			1,000
Impaired Financing Receivable, with Related Allowance, Recorded Investment	16,000		26,000
Unpaid principal balance with allowance	16,000		26,000
Impaired Financing Receivable, Related Allowance	2,000		26,000
Average recorded investment with an allowance	16,000		29,000
Interest income recognized with an allowance	1,000
Impaired Financing Receivable, Recorded Investment	16,000		73,000
Unpaid principal balance	16,000		73,000
Impaired Financing Receivable, Average Recorded Investment	16,000		68,000
Impaired Financing Receivable, Interest Income, Accrual Method	1,000		1,000
Commercial Portfolio Segment [Member] \| Agricultural Loans [Member]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	257,000		260,000
Unpaid principal balance with no related allowance recorded	257,000		260,000
Average recorded investment with no related allowance recorded	259,000		262,000
Interest income recognized with no related allowance recorded	15,000		20,000
Impaired Financing Receivable, with Related Allowance, Recorded Investment
Unpaid principal balance with allowance
Impaired Financing Receivable, Related Allowance
Average recorded investment with an allowance
Interest income recognized with an allowance
Impaired Financing Receivable, Recorded Investment	257,000		260,000
Unpaid principal balance	257,000		260,000
Impaired Financing Receivable, Average Recorded Investment	259,000		262,000
Impaired Financing Receivable, Interest Income, Accrual Method	15,000		20,000
Commercial Portfolio Segment [Member] \| Real Estate Loan [Member]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,985,000		1,976,000
Unpaid principal balance with no related allowance recorded	2,422,000		2,622,000
Average recorded investment with no related allowance recorded	1,806,000		2,057,000
Interest income recognized with no related allowance recorded	18,000
Impaired Financing Receivable, with Related Allowance, Recorded Investment	603,000		1,154,000
Unpaid principal balance with allowance	811,000		1,154,000
Impaired Financing Receivable, Related Allowance	152,000		371,000
Average recorded investment with an allowance	542,000		1,203,000
Interest income recognized with an allowance
Impaired Financing Receivable, Recorded Investment	2,588,000		3,130,000
Unpaid principal balance	3,233,000		3,776,000
Impaired Financing Receivable, Average Recorded Investment	2,348,000		3,260,000
Impaired Financing Receivable, Interest Income, Accrual Method	18,000
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	204,000		221,000
Unpaid principal balance with no related allowance recorded	204,000		221,000
Average recorded investment with no related allowance recorded	213,000		232,000
Interest income recognized with no related allowance recorded
Impaired Financing Receivable, with Related Allowance, Recorded Investment	709,000		808,000
Unpaid principal balance with allowance	709,000		808,000
Impaired Financing Receivable, Related Allowance	248,000		269,000
Average recorded investment with an allowance	726,000		822,000
Interest income recognized with an allowance	6,000		8,000
Impaired Financing Receivable, Recorded Investment	913,000		1,029,000
Unpaid principal balance	913,000		1,029,000
Impaired Financing Receivable, Average Recorded Investment	939,000		1,054,000
Impaired Financing Receivable, Interest Income, Accrual Method	6,000		8,000
Residential Portfolio Segment [Member] \| Real Estate Loan [Member]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,390,000		1,347,000
Unpaid principal balance with no related allowance recorded	1,401,000		1,359,000
Average recorded investment with no related allowance recorded	1,334,000		1,346,000
Interest income recognized with no related allowance recorded	57,000		79,000
Impaired Financing Receivable, with Related Allowance, Recorded Investment	242,000		245,000
Unpaid principal balance with allowance	242,000		245,000
Impaired Financing Receivable, Related Allowance	53,000		54,000
Average recorded investment with an allowance	243,000		246,000
Interest income recognized with an allowance	8,000		11,000
Impaired Financing Receivable, Recorded Investment	1,632,000		1,592,000
Unpaid principal balance	1,643,000		1,604,000
Impaired Financing Receivable, Average Recorded Investment	1,577,000		1,592,000
Impaired Financing Receivable, Interest Income, Accrual Method	65,000		90,000
Residential Portfolio Segment [Member] \| Equity Lines of Credit [Member]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	197,000		199,000
Unpaid principal balance with no related allowance recorded	197,000		199,000
Average recorded investment with no related allowance recorded	94,000		156,000
Interest income recognized with no related allowance recorded
Impaired Financing Receivable, with Related Allowance, Recorded Investment	108,000		113,000
Unpaid principal balance with allowance	108,000		113,000
Impaired Financing Receivable, Related Allowance	25,000		31,000
Average recorded investment with an allowance	111,000		115,000
Interest income recognized with an allowance
Impaired Financing Receivable, Recorded Investment	305,000		312,000
Unpaid principal balance	305,000		312,000
Impaired Financing Receivable, Average Recorded Investment	205,000		271,000
Impaired Financing Receivable, Interest Income, Accrual Method
Consumer Portfolio Segment [Member] \| Automobile Loan [Member]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	121,000		65,000
Unpaid principal balance with no related allowance recorded	121,000		65,000
Average recorded investment with no related allowance recorded	54,000		21,000
Interest income recognized with no related allowance recorded
Impaired Financing Receivable, with Related Allowance, Recorded Investment
Unpaid principal balance with allowance
Impaired Financing Receivable, Related Allowance
Average recorded investment with an allowance
Interest income recognized with an allowance
Impaired Financing Receivable, Recorded Investment	121,000		65,000
Unpaid principal balance	121,000		65,000
Impaired Financing Receivable, Average Recorded Investment	54,000		21,000
Impaired Financing Receivable, Interest Income, Accrual Method
Consumer Portfolio Segment [Member] \| Other Loans [Member]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment
Unpaid principal balance with no related allowance recorded
Average recorded investment with no related allowance recorded
Interest income recognized with no related allowance recorded
Impaired Financing Receivable, with Related Allowance, Recorded Investment
Unpaid principal balance with allowance
Impaired Financing Receivable, Related Allowance
Average recorded investment with an allowance
Interest income recognized with an allowance
Impaired Financing Receivable, Recorded Investment
Unpaid principal balance
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, Interest Income, Accrual Method
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4,153,000		4,115,000
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,678,000		2,346,000
Impaired Financing Receivable, Related Allowance	480,000		751,000
Impaired Financing Receivable, Recorded Investment	5,832,000		6,461,000
Unpaid principal balance	6,488,000		7,119,000
Impaired Financing Receivable, Average Recorded Investment	5,398,000	$ 6,892,000	6,528,000
Impaired Financing Receivable, Interest Income, Accrual Method	$ 105,000	$ 89,000	$ 119,000

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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953550-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

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