Note 2 - Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net income	$ 21,274	$ 21,418	$ 18,006	$ 18,044	$ 18,134	$ 13,718	$ 60,698	$ 49,896
Denominator:
Basic earnings per common share - weighted-average shares (in shares)	82,907			82,672			82,835	82,472
Effect of dilutive stock options (in shares)	465			607			545	626
Diluted earnings per common share - weighted-average shares and assumed conversions (in shares)	83,372			83,279			83,380	83,098
Basic earnings per common share (in dollars per share)	$ 0.26			$ 0.22			$ 0.73	$ 0.61
Diluted earnings per common share (in dollars per share)	$ 0.26			$ 0.22			$ 0.73	$ 0.60