Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Parent Company [Member]
Allowance for doubtful accounts receivable	$ 5,016	$ 4,523
Straight-line rent receivable allowance	685	652
Deferred costs accumulated amortization	84,728	81,822
Accumulated amortization of acquired lease intangible assets	38,670	36,112
Accumulated accretion of acquired lease intangible liabilities	14,930	13,993
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	94,323,823	94,108,061
Exchangeable operating partnership units aggregate redemption value	10,490	9,833
Treasury stock, shares held at cost	443,514	425,246
Partnership Interest [Member]
Allowance for doubtful accounts receivable	5,016	4,523
Straight-line rent receivable allowance	685	652
Deferred costs accumulated amortization	84,728	81,882
Accumulated amortization of acquired lease intangible assets	38,670	36,112
Accumulated accretion of acquired lease intangible liabilities	$ 14,930	$ 13,993
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	94,323,823	94,108,061
Limited partner units, outstanding	154,170	154,170