Note 8 - Loans - Loan Balances and Allowance for Loan Losses for Each Impairment Method (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loans receivable: individually evaluated	$ 9,511	$ 10,860
Loans receivable: collectively evaluated	806,202	740,975
Loans receivable	815,713	751,835
Allowance for loan losses: individually evaluated	1,279	674
Allowance for loan losses: collectively evaluated	7,078	7,401
Allowance for loan losses	8,856	8,473	$ 7,889	$ 7,336
Residential Portfolio Segment [Member]
Loans receivable: individually evaluated	1,286	821
Loans receivable: collectively evaluated	446,000	419,952
Loans receivable	447,286	420,773
Allowance for loan losses: individually evaluated	122	0
Allowance for loan losses: collectively evaluated	3,841	3,890
Allowance for loan losses	3,963	3,890	3,418	3,653
Residential Portfolio Segment [Member] | Real Estate Loan [Member] | Senior Lien [Member]
Loans receivable: individually evaluated	984	753
Loans receivable: collectively evaluated	359,003	333,349
Loans receivable	359,987	334,102
Allowance for loan losses: individually evaluated	0	0
Allowance for loan losses: collectively evaluated	3,200	3,033
Allowance for loan losses	3,200	3,033	2,645	2,941
Residential Portfolio Segment [Member] | Real Estate Loan [Member] | Junior Lien [Member]
Loans receivable: individually evaluated	302	68
Loans receivable: collectively evaluated	25,023	23,638
Loans receivable	25,325	23,706
Allowance for loan losses: individually evaluated	122	0
Allowance for loan losses: collectively evaluated	102	258
Allowance for loan losses	224	258	219	176
Residential Portfolio Segment [Member] | Home Equity Line of Credit 1 [Member]
Loans receivable: individually evaluated	0	0
Loans receivable: collectively evaluated	35,758	38,057
Loans receivable	35,758	38,057
Allowance for loan losses: individually evaluated	0	0
Allowance for loan losses: collectively evaluated	296	350
Allowance for loan losses	296	350	347	322
Residential Portfolio Segment [Member] | Construction Loans [Member]
Loans receivable: individually evaluated	0	0
Loans receivable: collectively evaluated	26,216	24,908
Loans receivable	26,216	24,908
Allowance for loan losses: individually evaluated	0	0
Allowance for loan losses: collectively evaluated	243	249
Allowance for loan losses	243	249	207	214
Commercial Portfolio Segment [Member]
Loans receivable: individually evaluated	8,205	10,016
Loans receivable: collectively evaluated	345,283	307,324
Loans receivable	353,488	317,340
Allowance for loan losses: individually evaluated	1,157	674
Allowance for loan losses: collectively evaluated	3,078	3,373
Allowance for loan losses	4,235	4,047	3,922	3,143
Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans receivable: individually evaluated	5,873	8,005
Loans receivable: collectively evaluated	153,393	142,463
Loans receivable	159,266	150,468
Allowance for loan losses: individually evaluated	919	528
Allowance for loan losses: collectively evaluated	1,665	1,852
Allowance for loan losses	2,584	2,380	1,939	1,758
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans receivable: individually evaluated	0	0
Loans receivable: collectively evaluated	14,527	14,287
Loans receivable	14,527	14,287
Allowance for loan losses: individually evaluated	0	0
Allowance for loan losses: collectively evaluated	150	162
Allowance for loan losses	150	162	58	283
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
Loans receivable: individually evaluated	568	212
Loans receivable: collectively evaluated	87,708	83,642
Loans receivable	88,276	83,854
Allowance for loan losses: individually evaluated	188	95
Allowance for loan losses: collectively evaluated	877	904
Allowance for loan losses	1,065	999	981	688
Commercial Portfolio Segment [Member] | Political Subdivisions [Member]
Loans receivable: individually evaluated	0	0
Loans receivable: collectively evaluated	59,287	38,068
Loans receivable	59,287	38,068
Allowance for loan losses: individually evaluated	0	0
Allowance for loan losses: collectively evaluated	0	0
Allowance for loan losses	0	0	0	0
Commercial Portfolio Segment [Member] | Loans Secured by Farmland [Member]
Loans receivable: individually evaluated	1,365	1,394
Loans receivable: collectively evaluated	5,890	5,900
Loans receivable	7,255	7,294
Allowance for loan losses: individually evaluated	50	51
Allowance for loan losses: collectively evaluated	55	59
Allowance for loan losses	105	110	106	165
Commercial Portfolio Segment [Member] | Multifamily 5 or More Residential [Member]
Loans receivable: individually evaluated	392	392
Loans receivable: collectively evaluated	7,321	7,504
Loans receivable	7,713	7,896
Allowance for loan losses: individually evaluated	0	0
Allowance for loan losses: collectively evaluated	172	241
Allowance for loan losses	172	241	675	87
Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans receivable: individually evaluated	7	13
Loans receivable: collectively evaluated	6,171	3,985
Loans receivable	6,178	3,998
Allowance for loan losses: individually evaluated	0	0
Allowance for loan losses: collectively evaluated	57	40
Allowance for loan losses	57	40	45	31
Commercial Portfolio Segment [Member] | Other Commercial Loans [Member]
Loans receivable: individually evaluated	0	0
Loans receivable: collectively evaluated	10,986	11,475
Loans receivable	10,986	11,475
Allowance for loan losses: individually evaluated	0	0
Allowance for loan losses: collectively evaluated	102	115
Allowance for loan losses	102	115	118	131
Consumer Portfolio Segment [Member]
Loans receivable: individually evaluated	20	23
Loans receivable: collectively evaluated	14,919	13,699
Loans receivable	14,939	13,722
Allowance for loan losses: individually evaluated	0	0
Allowance for loan losses: collectively evaluated	159	138
Allowance for loan losses	159	138	122	145
Unallocated Financing Receivables [Member]
Allowance for loan losses	$ 499	$ 398	$ 427	$ 395