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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income	$ 18,044	$ 18,134	$ 13,718	$ 16,587	$ 15,190	$ 13,546	$ 49,896	$ 45,323
Denominator:
Basic earnings per common share - weighted-average shares (in shares)	82,672			81,982			82,472	81,912
Effect of dilutive stock options (in shares)	607			719			626	706
Diluted earnings per common share - weighted-average shares and assumed conversions (in shares)	83,279			82,701			83,098	82,618
Basic earnings per common share (in dollars per share)	$ 0.22			$ 0.20			$ 0.61	$ 0.55
Diluted earnings per common share (in dollars per share)	$ 0.22			$ 0.20			$ 0.60	$ 0.55