Note 4 - Net Income Per Common Share - Computation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income	$ 33,372	$ 50,867	$ 63,655
Basic - weighted-average shares outstanding: (in shares)	27,617,627	26,737,425	26,866,985
Employee stock options and other (in shares)	35,472	158,932	182,438
Diluted - weighted-average shares outstanding: (in shares)	27,653,099	26,896,357	27,049,423
Basic (in dollars per share)	$ 1.21	$ 1.90	$ 2.37
Diluted (in dollars per share)	$ 1.21	$ 1.89	$ 2.35