Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Parent Company [Member]
Allowance for doubtful accounts receivable	$ 3,124,000	$ 3,442,000
Straight-line rent receivable allowance	1,871,000	2,075,000
Deferred costs accumulated amortization	71,385,000	71,265,000
Accumulated amortization of acquired lease intangible assets	16,705,000	15,588,000
Accumulated accretion of acquired lease intangible liabilities	5,143,000	4,750,000
Preferred stock, par value per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	32,000,000	32,000,000
Preferred units of Series 3-6, units issued	13,000,000	11,000,000
Preferred units of Series 3-6, units outstanding	13,000,000	11,000,000
Preferred stock, liquidation preferences per share	$ 25	$ 25
Common stock, par value per share	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	89,929,528	89,921,858
Preferred units, aggregate redemption value	50,000	50,000
Exchangeable operating partnership units aggregate redemption value	7,880,000	6,665,000
Treasury stock, shares held at cost	315,867	338,714
Partnership Interest [Member]
Allowance for doubtful accounts receivable	3,124,000	3,442,000
Straight-line rent receivable allowance	1,871,000	2,075,000
Deferred costs accumulated amortization	71,385,000	71,265,000
Accumulated amortization of acquired lease intangible assets	16,705,000	15,558,000
Accumulated accretion of acquired lease intangible liabilities	5,143,000	4,750,000
Series D preferred units, par value	$ 100	$ 100
Series D units issued	500,000	500,000
Series D preferred units outstanding	500,000	500,000
Preferred units of general partner par value per unit	$ 0.01	$ 0.01
Preferred units of Series 3-6, units issued	13,000,000	11,000,000
Preferred units of Series 3-6, units outstanding	13,000,000	11,000,000
Preferred stock, liquidation preferences per share	$ 25	$ 25
General partner units, outstanding	89,929,528	89,921,858
Limited partner units, outstanding	177,164	177,164