Note 17 - Preferred Stock, Common Stock and Convertible Unit Transactions (Details Textual)	1 Months Ended	12 Months Ended
	Feb. 28, 2015 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 shares
Preferred Stock, Liquidation Preference, Value		$ 800,000,000	$ 800,000,000
Common Stock, Par or Stated Value Per Share | $ / shares		$ 0.01	$ 0.01
ATM Program, Amount Available		$ 211,900,000
Stock Repurchased During Period, Shares | shares		257,477	179,696	128,147
Stockholders' Equity Attributable to Noncontrolling Interest		$ 146,735,000	$ 135,651,000
Partners' Capital Account, Units, Converted | shares		900,000
ATM Program [Member]
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.01
Maximum Aggregate Sales Price	$ 500,000,000
Stock Issued During Period, Shares, New Issues | shares		9,806,377
Proceeds from Issuance of Common Stock		$ 285,200,000
Payments of Stock Issuance Costs		$ 2,900,000
Redeemable Series H Preferred Stock [Member]
Preferred Stock, Liquidation Preference, Value			$ 5,800,000
Series I, J or K Preferred Stock [Member]
Number of Votes		1,000
Number of Proxies		1,000
Number of Votes, Depositary		1
Series I Preferred Stock [Member]
Preferred Stock, Liquidation Preference, Value		$ 400,000,000
Preferred Stock, Liquidation Preference Per Share | $ / shares		$ 25,000
Stock Issued During Period, Shares, New Issues | shares			16,000,000
Series J Preferred Stock [Member]
Preferred Stock, Liquidation Preference, Value		$ 225,000,000
Preferred Stock, Liquidation Preference Per Share | $ / shares		$ 25,000
Stock Issued During Period, Shares, New Issues | shares			9,000,000
Series K Preferred Stock [Member]
Preferred Stock, Liquidation Preference, Value		$ 175,000,000
Preferred Stock, Liquidation Preference Per Share | $ / shares		$ 25,000
Stock Issued During Period, Shares, New Issues | shares			7,000,000
Depositary Share [Member]
Preferred Stock, Liquidation Preference Per Share | $ / shares		$ 25
Convertible Units [Member]
Stockholders' Equity Attributable to Noncontrolling Interest		$ 24,100,000