Note 3 - 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, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income	$ 16,587	$ 15,190	$ 13,546	$ 15,257	$ 13,702	$ 10,331	$ 45,323	$ 39,290
Denominator:
Basic earnings per common share - weighted-average shares (in shares)	54,655			54,661			54,608	54,615
Effect of dilutive stock options (in shares)	479			533			470	536
Diluted earnings per common share - weighted-average shares and assumed conversions (in shares)	55,134			55,194			55,078	55,151
Basic earnings per common share (in dollars per share)	$ 0.30			$ 0.28			$ 0.83	$ 0.72
Diluted earnings per common share (in dollars per share)	$ 0.30			$ 0.28			$ 0.82	$ 0.71