Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Consolidated Balance Sheets [Abstract]
Tenant and other receivables, allowance for doubtful accounts	$ 1,370	$ 1,766
Accrued rental income, allowance	2,631	2,515
Unsecured senior notes, discount	9,631	9,814
Unsecured exchangeable senior notes, discount	$ 2,720	$ 3,462
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	149,463,241	148,186,511
Common stock, shares outstanding	149,384,341	148,107,611
Treasury common stock at cost, shares	78,900	78,900