Note 24 - Income Taxes - Taxable Characteristics of Distributions Paid (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Dividends distributed, amount	$ 380,316	$ 377,651	$ 528,606
Series I Preferred Stock [Member]
Ordinary income, amount	$ 0	$ 0	$ 7,389
Ordinary income, percent	0.00%	0.00%	77.00%
Capital gain, amount	$ 0	$ 0	$ 2,207
Capital gain, percent	0.00%	0.00%	23.00%
Dividends distributed, amount	$ 0	$ 0	$ 9,596
Dividends distributed, percent	0.00%	0.00%	100.00%
Series J Preferred Stock [Member]
Ordinary income, amount	$ 0	$ 0	$ 11,541
Ordinary income, percent	0.00%	0.00%	77.00%
Capital gain, amount	$ 0	$ 0	$ 3,447
Capital gain, percent	0.00%	0.00%	23.00%
Dividends distributed, amount	$ 0	$ 0	$ 14,988
Dividends distributed, percent	0.00%	0.00%	100.00%
Series K Preferred Stock [Member]
Ordinary income, amount	$ 0	$ 0	$ 6,927
Ordinary income, percent	0.00%	0.00%	77.00%
Capital gain, amount	$ 0	$ 0	$ 2,069
Capital gain, percent	0.00%	0.00%	23.00%
Dividends distributed, amount	$ 0	$ 0	$ 8,996
Dividends distributed, percent	0.00%	0.00%	100.00%
Series L Preferred Stock [Member]
Ordinary income, amount	$ 11,185	$ 4,382	$ 8,879
Ordinary income, percent	97.00%	38.00%	77.00%
Capital gain, amount	$ 346	$ 7,149	$ 2,652
Capital gain, percent	3.00%	62.00%	23.00%
Dividends distributed, amount	$ 11,531	$ 11,531	$ 11,531
Dividends distributed, percent	100.00%	100.00%	100.00%
Series M Preferred Stock [Member]
Ordinary income, amount	$ 13,469	$ 5,277	$ 10,692
Ordinary income, percent	97.00%	38.00%	77.00%
Capital gain, amount	$ 417	$ 8,609	$ 3,194
Capital gain, percent	3.00%	62.00%	23.00%
Dividends distributed, amount	$ 13,886	$ 13,886	$ 13,886
Dividends distributed, percent	100.00%	100.00%	100.00%
Common Stock 1 [Member]
Ordinary income, amount	$ 273,272	$ 133,849	$ 328,726
Ordinary income, percent	77.00%	38.00%	70.00%
Capital gain, amount	$ 10,647	$ 214,863	$ 98,618
Capital gain, percent	3.00%	61.00%	21.00%
Dividends distributed, amount	$ 354,899	$ 352,234	$ 469,609
Dividends distributed, percent	100.00%	100.00%	100.00%
Return of capital, amount	$ 70,980	$ 3,522	$ 42,265
Return of capital, percent	20.00%	1.00%	9.00%