Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified			3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Series G Cumulative Redeemable Preferred Stock	Dec. 31, 2012 Series G Cumulative Redeemable Preferred Stock	Mar. 31, 2013 Series H Cumulative Redeemable Preferred Stock	Dec. 31, 2012 Series H Cumulative Redeemable Preferred Stock
Preferred Stock, Value, Issued			$ 96,155	$ 96,155	$ 96,256	$ 96,256
Variable Interest Entity, Consolidated, Carrying Amount, Assets		337,000
Preferred stock, $.01 par value, 30,000,000 shares authorized:
Preferred stock dividend rate percentage			6.875%	6.875%	6.375%	6.375%
Preferred stock, par value	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 10.00
Preferred stock, shares authorized	30,000,000	30,000,000	4,600,000	4,600,000	4,000,000	4,000,000
Preferred stock, shares issued			4,000,000	4,000,000	4,000,000	4,000,000
Preferred stock, shares outstanding			4,000,000	4,000,000	4,000,000	4,000,000
Preferred Stock Liquidation preference			$ 100,000	$ 100,000	$ 100,000	$ 100,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	75,349,705	74,926,981
Common stock, shares outstanding	75,349,705	74,926,981