Note 3 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans - Loans Past Due 90 Days or More and Impaired Loans (Details) - USD ($) $ in Thousands		9 Months Ended			12 Months Ended
		Sep. 30, 2017		Sep. 30, 2016	Dec. 31, 2016
Loans past due 90 days or more and still accruing		$ 250	[1]	$ 195	$ 63	[1]
Ratio of loans past due 90 days or more and still accruing to loans, net of unearned income and deferred fees and costs		0.04%		0.03%	0.01%
Accruing restructured loans		$ 4,815		$ 4,662	$ 3,769
Impaired loans:
Impaired loans with no valuation allowance		10,522	[2]	9,290	8,269	[2]
Impaired loans with a valuation allowance		1,637	[2]	620	904	[2]
Total impaired loans		12,159	[2]	9,910	9,173	[2]
Valuation allowance		(186)		(27)	(26)
Impaired loans, net of allowance		11,973		9,883	9,147
Average recorded investment in impaired loans(1)	[3],[4]	12,541		12,908	11,585	[5]
Interest income recognized on impaired loans, after designation as impaired		387		476	553	[5]
Amount of income recognized on a cash basis		$ 0		$ 0	$ 0

[1] Only classes with past-due or nonaccrual loans are shown.

[2] Recorded investment is net of charge-offs and interest paid while a loan is in nonaccrual status.

[3] Recorded investment is net of charge-offs and interest paid while a loan is in nonaccrual status.

[4] Recorded investment is net of charge-offs and interest paid while a loan is in nonaccrual status.

[5] Only classes with impaired loans are shown.