Note 4 - Investment Securities (Details Textual) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities Pledged as Collateral	$ 122,700,000	$ 140,600,000
Cash, FDIC Insured Amount	250,000	250,000
Securities Sold under Agreements to Repurchase	13,445,000	19,114,000
Available-for-sale Securities, Amortized Cost Basis	196,510,000	190,803,000
Call Option [Member]
Available-for-sale Securities, Amortized Cost Basis	133,800,000	93,800,000
Callable Within One Year [Member]
Available-for-sale Securities, Amortized Cost Basis	$ 24,900,000	$ 27,400,000