Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Parent Company [Member]
Allowance for doubtful accounts receivable	$ 3,697	$ 3,915
Straight-line rent receivable allowance	568	870
Deferred costs accumulated amortization	71,640	69,224
Accumulated amortization of acquired lease intangible assets	21,104	19,148
Accumulated accretion of acquired lease intangible liabilities	7,393	6,636
Preferred stock, par value per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	30,000,000	30,000,000
Preferred units of Series 6-7, units issued	13,000,000	13,000,000
Preferred units of Series 6-7, units outstanding	13,000,000	13,000,000
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	91,397,030	90,394,486
Exchangeable operating partnership units aggregate redemption value	9,374	8,348
Treasury stock, shares held at cost	333,446	335,347
Partnership Interest [Member]
Allowance for doubtful accounts receivable	3,697	3,915
Straight-line rent receivable allowance	568	870
Deferred costs accumulated amortization	71,640	69,224
Accumulated amortization of acquired lease intangible assets	21,104	19,148
Accumulated accretion of acquired lease intangible liabilities	$ 7,393	$ 6,636
Preferred units of general partner par value per unit	$ 0.01	$ 0.01
Preferred units of Series 6-7, units issued	13,000,000	13,000,000
Preferred units of Series 6-7, units outstanding	13,000,000	13,000,000
Preferred stock, liquidation preferences per share	$ 25	$ 25
General partner units, outstanding	91,397,030	90,394,486
Limited partner units, outstanding	177,164	177,164