Note 3 - Net Income Per Common Share - Computation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Net income	$ 13,984	$ 15,511
Basic - weighted-average shares outstanding: (in shares)	26,776,806	26,963,366
Employee stock options and other (in shares)	152,834	213,673
Diluted - weighted-average shares outstanding: (in shares)	26,929,640	27,177,039
Basic (in dollars per share)	$ 0.52	$ 0.58
Diluted (in dollars per share)	$ 0.52	$ 0.57