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		3 Months Ended			12 Months Ended
		Mar. 31, 2017		Mar. 31, 2016	Dec. 31, 2016
Loans past due 90 days or more and still accruing		$ 63	[1]	$ 328	$ 63
Ratio of loans past due 90 days or more and still accruing to loans, net of unearned income and deferred fees		0.01%		0.05%	0.01%
Accruing restructured loans		$ 3,747		$ 7,724	$ 3,769
Impaired loans:
Impaired loans with no valuation allowance		8,172	[2]	12,171	8,269	[2]
Impaired loans with a valuation allowance		894	[2]	1,818	904	[2]
Total impaired loans		9,066	[2]	13,989	9,173	[2]
Valuation allowance		(25)		(80)	(26)
Impaired loans, net of allowance		9,041		13,909	9,147
Average recorded investment in impaired loans(1)	[3],[4]	9,123		14,796	11,585	[5]
Interest income recognized on impaired loans, after designation as impaired		67		125	553	[5]
Amount of income recognized on a cash basis		$ 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.