Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Preferred stock, $.01 par value, 30,000,000 shares authorized:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	30,000,000	30,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	68,349,843	58,819,717
Common stock, shares outstanding	68,349,843	58,819,717
Series A Cumulative Redeemable Preferred Stock
Preferred stock, $.01 par value, 30,000,000 shares authorized:
Preferred stock dividend rate percentage	7.45%	7.45%
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	1,500,000	1,500,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Series E Cumulative Redeemable Preferred Stock
Preferred stock, $.01 par value, 30,000,000 shares authorized:
Preferred stock dividend rate percentage	7.80%	7.80%
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	1,610,000	1,610,000
Preferred stock, shares issued	1,610,000	1,610,000
Preferred stock, shares outstanding	1,610,000	1,610,000
Preferred Stock Liquidation preference	$ 40,250	$ 40,250
Series F Cumulative Redeemable Preferred Stock
Preferred stock, $.01 par value, 30,000,000 shares authorized:
Preferred stock dividend rate percentage	7.50%	7.50%
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	3,450,000	3,450,000
Preferred stock, shares issued	3,450,000	3,450,000
Preferred stock, shares outstanding	3,450,000	3,450,000
Preferred Stock Liquidation preference	86,250	86,250
Series G Cumulative Redeemable Preferred Stock
Preferred stock, $.01 par value, 30,000,000 shares authorized:
Preferred stock dividend rate percentage	6.875%
Preferred stock, par value	$ 0.01
Preferred stock, shares authorized	4,000,000	0
Preferred stock, shares issued	4,000,000	0
Preferred stock, shares outstanding	4,000,000	0
Preferred Stock Liquidation preference	$ 100,000	$ 0