Note 21 - Income Taxes (Details) - Taxable Characteristics of Distributions Paid (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Note 21 - Income Taxes (Details) - Taxable Characteristics of Distributions Paid [Line Items]
Dividends distributed, amount	$ 427,873	$ 400,354	$ 382,722
Series F Preferred Stock [Member]
Note 21 - Income Taxes (Details) - Taxable Characteristics of Distributions Paid [Line Items]
Ordinary income, amount			9,116
Ordinary income, percent			94.00%
Capital gain, amount			582
Capital gain, percent			6.00%
Dividends distributed, amount			9,698
Dividends distributed, percent			100.00%
Series G Preferred Stock [Member]
Note 21 - Income Taxes (Details) - Taxable Characteristics of Distributions Paid [Line Items]
Ordinary income, amount			33,046
Ordinary income, percent			94.00%
Capital gain, amount			2,109
Capital gain, percent			6.00%
Dividends distributed, amount			35,155
Dividends distributed, percent			100.00%
Series H Preferred Stock [Member]
Note 21 - Income Taxes (Details) - Taxable Characteristics of Distributions Paid [Line Items]
Ordinary income, amount	6,762	8,694	11,351
Ordinary income, percent	56.00%	72.00%	94.00%
Capital gain, amount	5,313	3,381	725
Capital gain, percent	44.00%	28.00%	6.00%
Dividends distributed, amount	12,075	12,075	12,076
Dividends distributed, percent	100.00%	100.00%	100.00%
Series I Preferred Stock [Member]
Note 21 - Income Taxes (Details) - Taxable Characteristics of Distributions Paid [Line Items]
Ordinary income, amount	13,440	17,280	12,847
Ordinary income, percent	56.00%	72.00%	94.00%
Capital gain, amount	10,560	6,720	820
Capital gain, percent	44.00%	28.00%	6.00%
Dividends distributed, amount	24,000	24,000	13,667
Dividends distributed, percent	100.00%	100.00%	100.00%
Series J Preferred Stock [Member]
Note 21 - Income Taxes (Details) - Taxable Characteristics of Distributions Paid [Line Items]
Ordinary income, amount	6,930	8,910	2,585
Ordinary income, percent	56.00%	72.00%	94.00%
Capital gain, amount	5,445	3,465	165
Capital gain, percent	44.00%	28.00%	6.00%
Dividends distributed, amount	12,375	12,375	2,750
Dividends distributed, percent	100.00%	100.00%	100.00%
Series K Preferred Stock [Member]
Note 21 - Income Taxes (Details) - Taxable Characteristics of Distributions Paid [Line Items]
Ordinary income, amount	5,513	6,064
Ordinary income, percent	56.00%	72.00%
Capital gain, amount	4,331	2,358
Capital gain, percent	44.00%	28.00%
Dividends distributed, amount	9,844	8,422
Dividends distributed, percent	100.00%	100.00%
Common Stock [Member]
Note 21 - Income Taxes (Details) - Taxable Characteristics of Distributions Paid [Line Items]
Ordinary income, amount	133,048	158,001	222,751
Ordinary income, percent	36.00%	46.00%	72.00%
Capital gain, amount	103,483	61,827	15,469
Capital gain, percent	28.00%	18.00%	5.00%
Return of capital	133,048	123,654	71,156
Return of capital	36.00%	36.00%	23.00%
Dividends distributed, amount	$ 369,579	$ 343,482	$ 309,376
Dividends distributed, percent	100.00%	100.00%	100.00%