Note 16 - Preferred Stock, Common Stock and Convertible Unit Transactions - Dividends Declared (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Stock (in dollars per share)	$ 1.12	$ 1.09	$ 1.035
Series I Preferred Stock [Member]
Preferred Shares (in dollars per share)	1.50	1.50	1.50
Series I Preferred Stock Redeemed [Member]
Preferred Shares (in dollars per share)		0.9625
Series J Preferred Stock [Member]
Preferred Shares (in dollars per share)	1.375	1.375	1.375
Series K Preferred Stock [Member]
Preferred Shares (in dollars per share)	1.40625	1.40625	1.40625
Series L Preferred Stock [Member]
Preferred Shares (in dollars per share)	1.28125	0.48047
Series M Preferred Stock [Member]
Preferred Shares (in dollars per share)	$ 1.3125	$ 0.0401