Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Tenant and other receivables, allowance for doubtful accounts	$ 1,766	$ 2,081
Accrued rental income, allowance	2,515	3,116
Unsecured senior notes, discount	9,814	8,402
Unsecured exchangeable senior notes, discount	$ 3,462	$ 8,249
Excess stock, par value	$ 0.01	$ 0.01
Excess stock, shares authorized	150,000,000	150,000,000
Excess stock, shares issued	0	0
Excess stock, shares outstanding	0	0
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	148,186,511	140,278,005
Common stock, shares outstanding	148,107,611	140,199,105
Treasury common stock at cost, shares	78,900	78,900