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								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net income available to common stockholders	$ 17,764	$ 19,898	$ 19,885	$ 23,420	$ 31,047	$ 27,406	$ 30,849	$ 29,872	$ 80,967	$ 119,174	$ 128,636
Earnings allocated to participating securities									(216)	(287)	(313)
Income attributable to common stock									$ 80,751	$ 118,887	$ 128,323
Weighted average common shares outstanding, including participating securities (in shares)									38,913	39,355	39,723
Weighted average participating securities (in shares)									(104)	(95)	(97)
Weighted average common shares outstanding (in shares)									38,809	39,260	39,626
Incremental shares from assumed conversions of options, deferred stock units, performance units and restricted stock (in shares)									153	216	260
Weighted average common and equivalent shares outstanding (in shares)									38,962	39,476	39,886
Earnings per common share:
Basic (in dollars per share)	$ 0.46	$ 0.51	$ 0.51	$ 0.6	$ 0.79	$ 0.7	$ 0.78	$ 0.76	$ 2.08	$ 3.03	$ 3.24
Diluted (in dollars per share)	$ 0.46	$ 0.51	$ 0.51	$ 0.59	$ 0.79	$ 0.7	$ 0.78	$ 0.75	$ 2.07	$ 3.01	$ 3.22