Note 16 - Preferred Stock, Common Stock and Convertible Unit Transactions - Dividends Declared (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common Stock (in dollars per share)	$ 1.12000	$ 1.12000	$ 1.09000
Series I Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.99583	1.50000	1.50000
Series I Preferred Stock Redeemed [Member]
Preferred Shares (in dollars per share)	0	0	0.96250
Series J Preferred Stock [Member]
Preferred Shares (in dollars per share)	1.37500	1.37500	1.37500
Series K Preferred Stock [Member]
Preferred Shares (in dollars per share)	0.93359	1.40625	1.40625
Series L Preferred Stock [Member]
Preferred Shares (in dollars per share)	1.28125	1.28125	0.48047
Series M Preferred Stock [Member]
Preferred Shares (in dollars per share)	$ 1.31250	$ 1.31250	$ 0.04010