Note 3 - Securities - Debt Securities by Maturity (Details)	Dec. 31, 2017 USD ($)
Due in one year or less	1.74%
Due in one year or less	$ 29,667,000
Due in one year or less	$ 29,675,000
Due from one to five years	2.12%
Due from one to five years	$ 65,093,000
Due from one to five years	$ 64,938,000
Due from five to ten years	2.52%
Due from five to ten years	$ 100,128,000
Due from five to ten years	$ 97,943,000
Due after ten years	2.90%
Due after ten years	$ 106,083,000
Due after ten years	$ 102,415,000
Total available for sale securities	2.46%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 341,948,000
Total available for sale securities	$ 335,744,000
Collateralized Mortgage Backed Securities [Member]
No single maturity, weighted average yield	2.17%
No single maturity, amortized cost	$ 38,967,000
No single maturity, fair value	$ 38,792,000
Other Debt and Equity Securities [Member]
No single maturity, weighted average yield	2.71%
No single maturity, amortized cost	$ 2,010,000
No single maturity, fair value	$ 1,981,000