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				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net income	$ 21,418	$ 18,006	$ 18,134	$ 13,718	$ 39,424	$ 31,852
Denominator:
Basic earnings per common share - weighted-average shares (in shares)	82,840		82,527		82,799	82,371
Effect of dilutive stock options (in shares)	557		606		585	647
Diluted earnings per common share - weighted-average shares and assumed conversions (in shares)	83,397		83,133		83,384	83,018
Basic earnings per common share (in dollars per share)	$ 0.26		$ 0.22		$ 0.48	$ 0.39
Diluted earnings per common share (in dollars per share)	$ 0.26		$ 0.22		$ 0.47	$ 0.38