CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
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 (in shares)	4,102,564	4,102,564
Preferred stock, Series C Cumulative Convertible Redeemable Preferred Stock, shares issued (in shares)	4,102,564	4,102,564
Preferred stock, Series C Cumulative Convertible Redeemable Preferred Stock, shares outstanding (in shares)	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 (in shares)	100,000,000	100,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	160,815,933	135,237,438
Common stock, shares outstanding (in shares)	160,815,933	135,237,438
Series A Cumulative Redeemable Preferred Stock
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, shares issued (in shares)	0	7,050,000
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, shares outstanding (in shares)	0	7,050,000
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, dividend rate (as a percent)		8.00%
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, liquidation preference (in dollars per share)		$ 25.00
Series D Cumulative Redeemable Preferred Stock
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, shares issued (in shares)	4,600,000	4,600,000
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, shares outstanding (in shares)	4,600,000	4,600,000
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, dividend rate (as a percent)	8.00%	8.00%
Preferred stock, 8.0% Cumulative Redeemable Preferred Stock, liquidation preference (in dollars per share)	$ 25.00	$ 25.00