Note 25 - Income Taxes - Taxable Characteristics of Distributions Paid (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Dividends distributed, amount	$ 542,267	$ 380,316	$ 377,651
Series I Preferred Stock [Member]
Ordinary income, amount	$ 9,657	$ 11,185	$ 4,382
Ordinary income, percent	84.00%	97.00%	38.00%
Capital gain, amount	$ 1,839	$ 346	$ 7,149
Capital gain, percent	16.00%	3.00%	62.00%
Dividends distributed, amount	$ 11,496	$ 11,531	$ 11,531
Dividends distributed, percent	100.00%	100.00%	100.00%
Series J Preferred Stock [Member]
Ordinary income, amount	$ 11,615	$ 13,469	$ 5,277
Ordinary income, percent	84.00%	97.00%	38.00%
Capital gain, amount	$ 2,212	$ 417	$ 8,609
Capital gain, percent	16.00%	3.00%	62.00%
Dividends distributed, amount	$ 13,827	$ 13,886	$ 13,886
Dividends distributed, percent	100.00%	100.00%	100.00%
Series K Preferred Stock [Member]
Ordinary income, amount	$ 418,725	$ 273,272	$ 133,849
Ordinary income, percent	81.00%	77.00%	38.00%
Capital gain, amount	$ 82,711	$ 10,647	$ 214,863
Capital gain, percent	16.00%	3.00%	61.00%
Dividends distributed, amount	$ 516,944	$ 354,899	$ 352,234
Dividends distributed, percent	100.00%	100.00%	100.00%
Common Stock 1 [Member]
Return of capital, amount	$ 15,508	$ 70,980	$ 3,522
Return of capital, percent	3.00%	20.00%	1.00%