Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Parent Company [Member]
Allowance for doubtful accounts receivable	$ 4,543	$ 3,922
Straight-line rent receivable allowance	509	547
Deferred costs accumulated amortization	79,504	73,231
Accumulated amortization of acquired lease intangible assets	35,505	25,591
Accumulated accretion of acquired lease intangible liabilities	13,013	10,102
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	93,243,593	92,333,161
Exchangeable operating partnership units aggregate redemption value	8,299	7,676
Treasury stock, shares held at cost	421,758	373,042
Partnership Interest [Member]
Allowance for doubtful accounts receivable	4,543	3,922
Straight-line rent receivable allowance	509	547
Deferred costs accumulated amortization	79,504	73,231
Accumulated amortization of acquired lease intangible assets	35,505	25,591
Accumulated accretion of acquired lease intangible liabilities	$ 13,013	$ 10,102
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	93,243,593	92,333,161
Limited partner units, outstanding	154,170	165,796