Note 13 - Stockholders' Equity - Dividends Declared Per Share (Details) - $ / shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Common Shares (in dollars per share)	$ 0.84	$ 0.81
Series I Preferred Stock [Member]
Depositary Shares (in dollars per share)	1.125	1.125
Series I Preferred Stock Redeemed [Member]
Depositary Shares (in dollars per share)		0.9625
Series J Preferred Stock [Member]
Depositary Shares (in dollars per share)	1.03125	1.03125
Series K Preferred Stock [Member]
Depositary Shares (in dollars per share)	1.05468	1.05468
Series L Preferred Stock [Member]
Depositary Shares (in dollars per share)	0.96093	0.16016
Series M Preferred Stock [Member]
Depositary Shares (in dollars per share)	$ 0.98439