Note 3 - Loans - Activity in Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance				$ 8,880				$ 8,202	$ 8,880	$ 8,202	$ 8,967
Negative provision for loan losses						$ (350)	$ (150)			(500)	(800)
Loans charged off									(1,288)	(616)	(901)
Recoveries									784	1,794	936
Balance	8,376				8,880				8,376	8,880	8,202
Commercial Portfolio Segment [Member]
Balance				1,299				892	1,299	892	475
Negative provision for loan losses									342	196	363
Loans charged off									(37)	(50)	(5)
Recoveries									106	261	59
Balance	1,710				1,299				1,710	1,299	892
Commercial Real Estate Portfolio Segment [Member]
Balance				4,676				4,032	4,676	4,032	4,894
Negative provision for loan losses									(622)	(192)	(1,223)
Loans charged off									(47)	(198)	(58)
Recoveries									73	1,034	419
Balance	4,080				4,676				4,080	4,676	4,032
Residential Portfolio Segment [Member]
Balance				2,452				2,900	2,452	2,900	3,426
Negative provision for loan losses									(958)	(599)	(129)
Loans charged off									(275)	(252)	(692)
Recoveries									524	403	295
Balance	1,743				2,452				1,743	2,452	2,900
Consumer Portfolio Segment [Member]
Balance				130				64	130	64	8
Negative provision for loan losses									943	92	(8)
Loans charged off									(663)	(95)	(51)
Recoveries									75	69	115
Balance	485				130				485	130	64
Agriculture Portfolio Segment [Member]
Balance				321				313	321	313	162
Negative provision for loan losses									297	6	213
Loans charged off									(266)	(13)	(95)
Recoveries									3	15	33
Balance	355				321				355	321	313
Other Portfolio Segment [Member]
Balance				$ 2				$ 1	2	1	2
Negative provision for loan losses									(2)	(3)	(16)
Loans charged off										(8)
Recoveries									3	12	15
Balance	$ 3				$ 2				$ 3	$ 2	$ 1