CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)			6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Series A Cumulative Redeemable Preferred Stock	Dec. 31, 2011 Series A Cumulative Redeemable Preferred Stock	Jun. 30, 2012 Series D Cumulative Redeemable Preferred Stock	Dec. 31, 2011 Series D Cumulative Redeemable Preferred Stock
Preferred stock, Series C Cumulative Convertible Redeemable Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, Series C Cumulative Convertible Redeemable Preferred Stock, shares authorized	4,102,564	4,102,564
Preferred stock, Series C Cumulative Convertible Redeemable Preferred Stock, shares issued	4,102,564	4,102,564
Preferred stock, Series C Cumulative Convertible Redeemable Preferred Stock, shares outstanding	4,102,564	4,102,564
Preferred stock, Series C Cumulative Convertible Redeemable Preferred Stock, liquidation preference (in dollars per share)	$ 24.375	$ 24.375
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, shares authorized	100,000,000	100,000,000
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, shares issued			7,050,000	7,050,000	4,600,000	4,600,000
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, shares outstanding			7,050,000	7,050,000	4,600,000	4,600,000
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, dividend rate (as a percent)			8.00%	8.00%	8.00%	8.00%
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, liquidation preference (in dollars per share)			$ 25.00	$ 25.00	$ 25.00	$ 25.00
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	135,229,303	117,265,090
Common stock, shares outstanding	135,229,303	117,265,090