Note 15 - Stockholders' Equity - Dividends Declared (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Common Stock (in dollars per share)	$ 0.28000	$ 0.28000	$ 0.84000	$ 0.84000
Series I Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.24583	0.37500	0.99583	1.12500
Series J Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.34375	0.34375	1.03125	1.03125
Series K Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.23047	0.35156	0.93359	1.05468
Series L Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.32031	0.32031	0.96093	0.96093
Series M Preferred Stock [Member]
Preferred Shares (in dollars per share)	$ 0.32813	$ 0.32813	$ 0.98439	$ 0.98439