Note 1 - Summary of Significant Accounting Policies - Net Income Per Share Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator for net income per share - basic:
Net income	$ 37,466	$ 37,260	$ 32,406
Denominator for net income per share - basic:
Weighted average common shares outstanding – basic (in shares)	25,422	25,170	24,809
Net income per share – basic (in dollars per share)	$ 1.47	$ 1.48	$ 1.30
Numerator for net income per share - diluted:
Weighted average common shares outstanding – basic (in shares)	25,422	25,170	24,809
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	25,640	25,696	25,653
Net income per share – diluted (in dollars per share)	$ 1.46	$ 1.45	$ 1.26
Common Stock [Member]
Numerator for net income per share - basic:
Net income	$ 37,466	$ 37,260	$ 32,406
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(18)	(57)	(109)
Net income attributable to common shareholders	$ 37,448	$ 37,203	$ 32,297
Denominator for net income per share - basic:
Weighted average common shares outstanding – basic (in shares)	25,422	25,170	24,809
Net income per share – basic (in dollars per share)	$ 1.47	$ 1.48	$ 1.30
Numerator for net income per share - diluted:
Net income attributable to common shareholders	$ 37,448	$ 37,203	$ 32,297
Weighted average common shares outstanding – basic (in shares)	25,422	25,170	24,809
Weighted average effect of dilutive securities – stock options (in shares)	218	526	844
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	25,640	25,696	25,653
Net income per share – diluted (in dollars per share)	$ 1.46	$ 1.45	$ 1.26