Note 8 - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	$ 8,037	$ 7,719	$ 7,841	$ 7,394
Provision for (credit to) loan losses	187	300	375	600
Charge-offs	(67)	(18)	(93)	(42)
Recoveries	35	34	69	83
Allowance for loan losses, end of period	8,192	8,035	8,192	8,035
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	2,829	1,978	2,711	1,459
Provision for (credit to) loan losses	4	191	107	698
Charge-offs	0	0	0	0
Recoveries	7	8	22	20
Allowance for loan losses, end of period	2,840	2,177	2,840	2,177
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	557	463	563	449
Provision for (credit to) loan losses	16	53	10	67
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Allowance for loan losses, end of period	573	516	573	516
Commercial Portfolio Segment [Member] | Secured by Commercial Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	2,431	2,577	2,410	2,646
Provision for (credit to) loan losses	278	61	298	(10)
Charge-offs	0	0	0	0
Recoveries	1	2	2	4
Allowance for loan losses, end of period	2,710	2,640	2,710	2,640
Commercial Portfolio Segment [Member] | Secured by Residential Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	835	1,344	816	1,760
Provision for (credit to) loan losses	(72)	(156)	(55)	(592)
Charge-offs	0	0	0	(3)
Recoveries	18	12	20	35
Allowance for loan losses, end of period	781	1,200	781	1,200
State and Political Subdivisions Portfolio Segment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	121	124	114	123
Provision for (credit to) loan losses	69	(1)	76	0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Allowance for loan losses, end of period	190	123	190	123
Retail Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	61	77	57	76
Provision for (credit to) loan losses	21	9	39	22
Charge-offs	(23)	(18)	(49)	(39)
Recoveries	8	10	20	19
Allowance for loan losses, end of period	67	78	67	78
Retail Portfolio Segment [Member] | Family Residential Mortgages [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	512	415	444	366
Provision for (credit to) loan losses	(3)	24	65	73
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Allowance for loan losses, end of period	509	439	509	439
Retail Portfolio Segment [Member] | Home Equity Loans and Lines [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	381	342	357	353
Provision for (credit to) loan losses	(27)	(25)	(7)	(39)
Charge-offs	(44)	0	(44)	0
Recoveries	1	2	5	5
Allowance for loan losses, end of period	311	319	311	319
Unallocated Financing Receivables [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, beginning of period	310	399	369	162
Provision for (credit to) loan losses	(99)	144	(158)	381
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Allowance for loan losses, end of period	$ 211	$ 543	$ 211	$ 543