Note 7 - Loans - Average Balance of Impaired Loans and Income Recognized on Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Average investment in impaired loans	$ 5,762	$ 8,037	$ 7,074	$ 8,948
Interest income recognized on impaired loans on a cash basis	110	77	224	225
Residential Portfolio Segment [Member]
Average investment in impaired loans	1,407	1,362	1,302	1,400
Interest income recognized on impaired loans on a cash basis	32	20	52	57
Residential Portfolio Segment [Member] | Real Estate Loan [Member] | Senior Lien [Member]
Average investment in impaired loans	1,057	1,067	997	1,102
Interest income recognized on impaired loans on a cash basis	21	17	39	47
Residential Portfolio Segment [Member] | Real Estate Loan [Member] | Junior Lien [Member]
Average investment in impaired loans	285	295	289	298
Interest income recognized on impaired loans on a cash basis	8	3	10	10
Residential Portfolio Segment [Member] | Home Equity Line of Credit [Member]
Average investment in impaired loans	65	0	16	0
Interest income recognized on impaired loans on a cash basis	3	0	3	0
Commercial Portfolio Segment [Member]
Average investment in impaired loans	4,355	6,658	5,768	7,530
Interest income recognized on impaired loans on a cash basis	78	56	172	167
Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Average investment in impaired loans	1,738	4,050	2,371	4,921
Interest income recognized on impaired loans on a cash basis	49	25	66	95
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
Average investment in impaired loans	1,202	184	1,460	346
Interest income recognized on impaired loans on a cash basis	4	4	38	11
Commercial Portfolio Segment [Member] | Loans Secured by Farmland [Member]
Average investment in impaired loans	1,359	1,355	1,443	1,359
Interest income recognized on impaired loans on a cash basis	23	11	42	27
Commercial Portfolio Segment [Member] | Multifamily 5 or More Residential [Member]
Average investment in impaired loans	0	392	0	392
Interest income recognized on impaired loans on a cash basis	0	0	0	0
Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Average investment in impaired loans	6	677	481	512
Interest income recognized on impaired loans on a cash basis	0	16	24	34
Commercial Portfolio Segment [Member] | Other Commercial Loans [Member]
Average investment in impaired loans	50	0	13	0
Interest income recognized on impaired loans on a cash basis	2	0	2	0
Consumer Portfolio Segment [Member]
Average investment in impaired loans	0	17	4	18
Interest income recognized on impaired loans on a cash basis	$ 0	$ 1	$ 0	$ 1