Note 15 - Stockholders' Equity - Dividends Declared (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Common Stock (in dollars per share)	$ 0.28000	$ 0.28000	$ 0.56000	$ 0.56000
Series I Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.37500	0.37500	0.75000	0.75000
Series J Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.34375	0.34375	0.68750	0.68750
Series K Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.35156	0.35156	0.70312	0.70312
Series L Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.32031	0.32031	0.64062	0.64062
Series M Preferred Stock [Member]
Preferred Shares (in dollars per share)	$ 0.32813	$ 0.32813	$ 0.65626	$ 0.65626