Note 16 - Preferred Stock, Common Stock and Convertible Unit Transactions (Details Textual) $ / shares in Units, $ in Thousands	1 Months Ended			12 Months Ended
	Feb. 24, 2020	Sep. 30, 2019 USD ($) $ / shares	Jan. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 shares	Feb. 22, 2018 USD ($) $ / shares
Preferred Stock, Par or Stated Value Per Share				$ 1.00	$ 1.00
Common Stock, Par or Stated Value Per Share				$ 0.01	$ 0.01
Stock Repurchased During Period, Shares | shares				223,609	278,566	232,304
Stock Repurchased During Period, Value | $					$ 75,126
Stockholders' Equity Attributable to Noncontrolling Interest, Ending Balance | $				$ 64,015	$ 77,249
Partners' Capital Account, Units, Converted | shares				600,000
Share Repurchase Program [Member]
Common Stock, Par or Stated Value Per Share							$ 0.01
Stock Repurchase Program, Authorized Amount | $							$ 300,000
Stock Repurchased During Period, Shares | shares				0	5,100,000
Stock Repurchased During Period, Value | $					$ 75,100
Stock Repurchased During Period, Weighted Average Price					$ 14.72
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $				$ 224,900
Share Repurchase Program [Member] | Subsequent Event [Member]
Stock Repurchase Program, Period in Force	2 years
ATM Program [Member]
Stock Issued During Period, Shares, New Issues | shares				9,514,544
Common Stock, Par or Stated Value Per Share		$ 0.01
Maximum Aggregate Sales Price | $		$ 500,000
Proceeds from Issuance of Common Stock | $				$ 200,100
Payments of Stock Issuance Costs | $				$ 1,800
Sale of Stock, Number of Shares Available for Future Issuance | shares				298,100,000
Series M Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues | shares			1,380,000
Preferred stock, Fractional Interest in Share of Stock			1.00%
Preferred Stock, Dividend Rate, Percentage				5.25%	5.25%
Preferred Stock, Par or Stated Value Per Share			$ 1.00	$ 1.00	$ 1.00
Proceeds from Issuance of Preferred Stock and Preference Stock | $			$ 33,400
Series M Cumulative Redeemable Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage			5.25%
Series I, J, K, L or M 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, Dividend Rate, Percentage					6.00%
Preferred Stock, Par or Stated Value Per Share					$ 1.00
Preferred Stock, Liquidation Preference Per Share				$ 25,000
Series J Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage					5.50%
Preferred Stock, Par or Stated Value Per Share					$ 1.00
Preferred Stock, Liquidation Preference Per Share				25,000
Depositary Share [Member]
Preferred Stock, Liquidation Preference Per Share				$ 25.00
Convertible Units [Member]
Stockholders' Equity Attributable to Noncontrolling Interest, Ending Balance | $				$ 13,300