Note 15 - Stockholders' Equity - Dividends Declared (Details) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Common Stock (in dollars per share)	$ 0.28	$ 0.28
Series I Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.375	0.375
Series J Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.3438	0.3438
Series K Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.3516	0.3516
Series L Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.3203	0.3203
Series M Preferred Stock [Member]
Preferred Shares (in dollars per share)	$ 0.3281	$ 0.3281