Note 5 - Loans - Allowance for Credit Losses and Recorded Investment in Financing Receivables (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance	$ 11,544	$ 11,180	$ 10,820
Charge-offs	(1,502)	(2,784)	(2,376)
Recoveries	933	3,148	2,736
Provision	950
Balance	11,925	11,544	11,180
Individually evaluated for impairment				$ 1,169	$ 1,461	$ 832
Collectively evaluated for impairment				10,756	10,083	10,348
Total	11,544	11,544	11,180	11,925	11,544	11,180
Individually evaluated for impairment				13,147	18,794	21,390
Collectively evaluated for impairment				866,688	785,417	695,249
Total gross loans				879,835	804,211	716,639
Commercial Portfolio Segment [Member]
Balance	2,849	2,493	3,503
Charge-offs	(51)	(1,106)	(700)
Recoveries	512	427	1,692
Provision	(818)	1,035	(2,002)
Balance	2,492	2,849	2,493
Individually evaluated for impairment				690	641	122
Collectively evaluated for impairment				1,802	2,208	2,371
Total	2,849	2,849	2,493	2,492	2,849	2,493
Individually evaluated for impairment				3,154	3,525	2,043
Collectively evaluated for impairment				145,934	150,319	130,762
Total gross loans				149,088	153,844	132,805
Commercial Real Estate Portfolio Segment [Member]
Balance	5,578	5,784	4,875
Charge-offs		(37)	(428)
Recoveries	27	2,480	771
Provision	814	(2,649)	566
Balance	6,419	5,578	5,784
Individually evaluated for impairment				77	85	97
Collectively evaluated for impairment				6,342	5,493	5,687
Total	5,578	5,578	5,784	6,419	5,578	5,784
Individually evaluated for impairment				1,403	3,125	7,733
Collectively evaluated for impairment				577,507	493,617	420,259
Total gross loans				578,910	496,742	427,992
Residential Portfolio Segment [Member]
Balance	1,716	1,577	1,670
Charge-offs	(483)	(829)	(749)
Recoveries	178	114	273
Provision	(242)	854	383
Balance	1,169	1,716	1,577
Individually evaluated for impairment				391	721	600
Collectively evaluated for impairment				778	995	977
Total	1,716	1,716	1,577	1,169	1,716	1,577
Individually evaluated for impairment				8,554	11,894	11,582
Collectively evaluated for impairment				93,358	90,050	94,387
Total gross loans				101,912	101,944	105,969
Consumer Portfolio Segment [Member]
Balance	955	770	450
Charge-offs	(968)	(812)	(499)
Recoveries	216	127
Provision	1,232	870	819
Balance	1,435	955	770
Individually evaluated for impairment				11	14	13
Collectively evaluated for impairment				1,424	941	757
Total	955	955	770	1,435	955	770
Individually evaluated for impairment				36	250	32
Collectively evaluated for impairment				49,889	51,431	49,841
Total gross loans				49,925	51,681	49,873
Unallocated Financing Receivables [Member]
Balance	446	556	322
Charge-offs
Recoveries
Provision	(36)	(110)	234
Balance	410	446	556
Individually evaluated for impairment
Collectively evaluated for impairment				410	446	556
Total	$ 446	$ 446	$ 556	410	446	556
Individually evaluated for impairment
Collectively evaluated for impairment
Total gross loans