Note 1 - Summary of Significant Accounting Policies - Net Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income, basic and diluted	$ (1,435)	$ 5,312	$ 4,482	$ 3,329	$ 2,545	$ 4,324	$ 3,556	$ 6,180	$ 11,688	$ 16,605	$ 14,992
Less preferred stock dividends and discount accretion											395
Net income available to common shareholders, basic and diluted									$ 11,688	$ 16,605	$ 14,597
Average common shares issued and outstanding, basic and diluted (in shares)	7,516	7,514	7,512	7,510	7,508	7,505	7,502	7,500	7,513	7,504	7,494
Net income per common share, basic and diluted (in dollars per share)	$ (0.19)	$ 0.71	$ 0.60	$ 0.44	$ 0.34	$ 0.58	$ 0.47	$ 0.82	$ 1.56	$ 2.21	$ 1.95