Note 18 - Stockholders' Equity (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021	[1]	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Stockholders' Equity Attributable to Parent, Ending Balance	$ 2,452,357	$ 2,342,448	$ 2,452,357	$ 2,342,448	$ 2,460,948		$ 2,418,144	$ 2,313,037	$ 2,294,283
Stockholders' Equity, Period Increase (Decrease), Total			34,200
Net Income (Loss) Attributable to Parent, Total	77,199	54,321	150,583	101,173
Share-based Payment Arrangement, Noncash Expense, Total			2,400
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan			1,725	1,707
Treasury Stock, Value, Acquired, Cost Method	63,529		63,529	12,880
Dividends, Common Stock, Cash	24,548	24,672	49,198	49,332
Other Comprehensive Income (Loss), Net of Tax, Total	$ 686	$ (1,524)	$ (2,938)	$ 6,051

[1] Balance sheet amounts previously reported for the impact of the initial adoption of CECL on January 1, 2021 have been corrected. The correction had an after-tax decrease to the cumulative effect of the change in accounting principle related to ASC326 of $2.3 million.