Note 2 - Earnings Per Common Share - Computation of Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Net income available to common stockholders	$ 30,849	$ 32,219	$ 60,721	$ 65,218
Earnings allocated to participating securities	(70)	(81)	(150)	(176)
Income attributable to common stock	$ 30,779	$ 32,138	$ 60,571	$ 65,042
Weighted average common shares outstanding, including participating securities (in shares)	39,379	39,781	39,469	39,786
Weighted average participating securities (in shares)	(89)	(100)	(98)	(107)
Weighted average common shares outstanding (in shares)	39,290	39,681	39,371	39,679
Incremental shares from assumed conversions of options, performance units and restricted shares (in shares)	176	192	225	214
Weighted average common and equivalent shares outstanding (in shares)	39,466	39,873	39,596	39,893
Earnings per common share:
Basic (in dollars per share)	$ 0.78	$ 0.81	$ 1.54	$ 1.64
Diluted (in dollars per share)	$ 0.78	$ 0.81	$ 1.53	$ 1.63