Note 6 - Earnings per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Earnings per Share
Net income	$ 23,624	$ 17,982
Basic EPS	$ 1.51	$ 1.14
Diluted EPS	$ 1.49	$ 1.12
Weighted average common shares outstanding	15,625,112	15,803,643
Weighted average common shares issuable upon exercise of stock options and under the employee stock purchase plan (in shares)	227,144	221,905
Weighted average common and common equivalent shares outstanding (in shares)	15,852,256	16,025,548