Note 19 - Stockholders' Equity (Details Textual) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Stockholders' Equity Attributable to Parent, Ending Balance	$ 2,374,723	$ 2,245,894	$ 2,374,723	$ 2,245,894	$ 2,342,448	$ 2,294,283	$ 2,199,297	$ 2,121,866
Stockholders' Equity, Period Increase (Decrease), Total			80,400,000
Net Income (Loss) Attributable to Parent, Total	56,794	72,835	157,967	211,758
Other Comprehensive Income (Loss), Net of Tax, Total	(1,964)	525	4,087	17,173
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan			2,573	2,522
Dividends, Common Stock, Cash	$ 24,682	$ 24,701	74,014	74,422
Payments for Repurchase of Common Stock			$ 12,880	$ 36,301