Note 6 - Net Income Per Common Share - Net Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income, basic and diluted	$ 5,641	$ 3,329
Average common shares issued and outstanding, basic and diluted (in shares)	7,518	7,510
Net income per common share, basic and diluted (in dollars per share)	$ 0.75	$ 0.44