Note 5 - Revenue From Contracts With Customers - Sources of Noninterest Income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net loss on sales of available for sale investment securities	[1]	$ 0	$ (1)	$ 0	$ (10)
Net realized gain on sales of equity investment securities	[1]	808	0	808	0
Gains on sale of mortgage loans, net	[1]	104	189	199	343
Income from company-owned life insurance	[1]	213	221	506	456
Other		89	76	109	198
Total noninterest income		5,973	5,102	11,174	10,353
Overdraft Fees [Member]
Service charges, commissions, fees, and trust income		968	969	1,924	1,896
Dormant Account Fees [Member]
Service charges, commissions, fees, and trust income		574	659	1,167	1,324
Service Charges on Checking and Savings Accounts [Member]
Service charges, commissions, fees, and trust income		304	328	618	638
Other Service Charges and Fees on Deposits [Member]
Service charges, commissions, fees, and trust income		51	56	100	112
Allotment Processing Fees [Member]
Service charges, commissions, fees, and trust income		677	651	1,397	1,366
Interchange Fees [Member]
Service charges, commissions, fees, and trust income		917	808	1,744	1,589
Other Service Charges, Commissions, and Fees, Other [Member]
Service charges, commissions, fees, and trust income	[2]	573	520	1,118	1,111
Fiduciary and Trust [Member]
Service charges, commissions, fees, and trust income		$ 695	$ 626	$ 1,484	$ 1,330

[1] Not within the scope of ASC Topic 606.

[2] Includes fees totaling $147 thousand and $139 thousand for the three months ended June 30, 2018 and 2017, respectively, and $289 thousand and $272 thousand for the six months ended June 30, 2018 and 2017, respectively, which are primarily servicing fees on loans originated for sale on the secondary market and are not within the scope of ASC Topic 606.