Note 16 - Preferred Stock, Common Stock and Convertible Unit Transactions (Details Textual) $ / shares in Units, $ in Thousands		1 Months Ended		12 Months Ended
	Sep. 06, 2017 shares	Jan. 31, 2018 USD ($) $ / shares shares	Feb. 28, 2015 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares		Dec. 31, 2016 USD ($) shares	Feb. 22, 2018 USD ($) $ / shares
Preferred Stock, Dividend Rate, Percentage
Preferred Stock, Par or Stated Value Per Share				$ 1	$ 1
Common Stock, Par or Stated Value Per Share				$ 0.01	$ 0.01
Stock Repurchased During Period, Shares | shares				278,566	232,304		257,477
Stock Repurchased During Period, Value | $				$ 75,126
Stockholders' Equity Attributable to Noncontrolling Interest, Ending Balance | $				$ 77,249	$ 127,903
Partners' Capital Account, Units, Converted | shares				900,000
ATM Program [Member]
Stock Issued During Period, Shares, New Issues | shares				0	0		9,806,377
Common Stock, Par or Stated Value Per Share			$ 0.01
Maximum Aggregate Sales Price | $			$ 500,000
Proceeds from Issuance of Common Stock | $							$ 285,200
Payments of Stock Issuance Costs | $							$ 2,900
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				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
Series M Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues | shares		1,380,000			9,200,000	[1]
Preferred stock, Fractional Interest in Share of Stock		0.001%
Preferred Stock, Dividend Rate, Percentage				5.25%	5.25%
Preferred Stock, Par or Stated Value Per Share		$ 1		$ 1	$ 1
Proceeds from Issuance of Preferred Stock and Preference Stock | $		$ 33,400
Preferred Stock, Liquidation Preference Per Share				$ 25,000
Series M Cumulative Redeemable Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage		5.25%
Series I Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage				6.00%	6.00%
Preferred Stock, Par or Stated Value Per Share				$ 1	$ 1
Stock Redeemed or Called During Period, Shares | shares	9,000,000				9,000,000	[2],[3]
Percentage of Preferred Stock Redeemed	56.25%
Preferred Stock, Liquidation Preference Per Share				$ 25,000
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 J Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage				5.50%	5.50%
Preferred Stock, Par or Stated Value Per Share				$ 1	$ 1
Preferred Stock, Liquidation Preference Per Share				$ 25,000
Series K Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage				5.625%	5.625%
Preferred Stock, Par or Stated Value Per Share				$ 1	$ 1
Preferred Stock, Liquidation Preference Per Share				$ 25,000
Series L Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues | shares					9,000,000
Preferred Stock, Dividend Rate, Percentage				5.125%	5.125%
Preferred Stock, Par or Stated Value Per Share				$ 1	$ 1
Preferred Stock, Liquidation Preference Per Share				25,000
Depositary Share [Member]
Preferred Stock, Liquidation Preference Per Share				$ 25
Convertible Units [Member]
Stockholders' Equity Attributable to Noncontrolling Interest, Ending Balance | $				$ 14,600

[1] Additionally, during January 2018, the underwriting financial institutions for the Class M issuance elected to exercise the over-allotment option and as a result, the Company issued an additional 1,380,000 Class M Depositary Shares, each representing a one-thousandth fractional interest in a share of the Company's 5.250% Class M Cumulative Redeemable Preferred Stock, $1.00 par value per share. The Company received net proceeds before expenses of $33.4 million from this offering.

[2] Redemption charges resulting from the difference between the redemption amount and the carrying amount of the respective preferred stock class on the Company' Consolidated Balance Sheets are accounted for in accordance with the FASB's guidance on Distinguishing Liabilities from Equity. These charges were subtracted from net income attributable to the Company to arrive at net income available to the Company's common shareholders and used in the calculation of earnings per share.

[3] The Company partially redeemed 9,000,000 depositary shares of its issued and outstanding Class I Preferred Stock, representing 56.25% of the issued and outstanding Class I Preferred Stock.