Note 2 - Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income	$ 18,134	$ 13,718	$ 15,190	$ 13,546	$ 31,852	$ 28,736
Denominator:
Basic earnings per common share - weighted-average shares (in shares)	55,018,000		54,616,000		54,914,000	54,585,000
Effect of dilutive stock options (in shares)	404,000		465,000		431,000	470,000
Diluted earnings per common share - weighted-average shares and assumed conversions (in shares)	55,422,000		55,081,000		55,345,000	55,055,000
Basic earnings per common share (in dollars per share)	$ 0.33		$ 0.28		$ 0.58	$ 0.53
Diluted earnings per common share (in dollars per share)	$ 0.33		$ 0.28		$ 0.58	$ 0.52
Basic earnings per common share - weighted-average shares (in shares)	55,018,000		54,616,000		54,914,000	54,585,000
Pro Forma [Member]
Numerator:
Net income	$ 18,134		$ 15,190		$ 31,852	$ 28,736
Denominator:
Basic earnings per common share - weighted-average shares (in shares)	82,527		81,924		82,371	81,877
Effect of dilutive stock options (in shares)	606		697		647	705
Diluted earnings per common share - weighted-average shares and assumed conversions (in shares)	83,133		82,621		83,018	82,582
Basic earnings per common share (in dollars per share)	$ 0.22		$ 0.19		$ 0.39	$ 0.35
Diluted earnings per common share (in dollars per share)	$ 0.22		$ 0.18		$ 0.38	$ 0.35
Basic earnings per common share - weighted-average shares (in shares)	82,527		81,924		82,371	81,877