Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Parent Company [Member]
Allowance for doubtful accounts receivable	$ 4,286	$ 3,922
Straight-line rent receivable allowance	716	547
Deferred costs accumulated amortization	76,838	73,231
Accumulated amortization of acquired lease intangible assets	30,930	25,591
Accumulated accretion of acquired lease intangible liabilities	12,130	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	92,357,585	92,333,161
Exchangeable operating partnership units aggregate redemption value	8,872	7,676
Treasury stock, shares held at cost	418,001	373,042
Partnership Interest [Member]
Allowance for doubtful accounts receivable	4,286	3,922
Straight-line rent receivable allowance	716	547
Deferred costs accumulated amortization	76,838	73,231
Accumulated amortization of acquired lease intangible assets	30,930	25,591
Accumulated accretion of acquired lease intangible liabilities	$ 12,130	$ 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	92,357,585	92,333,161
Limited partner units, outstanding	159,338	165,796