Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Document Period End Date	Sep. 30, 2015
Parent Company [Member]
Allowance for doubtful accounts receivable	$ 5,377	$ 4,523
Straight-line rent receivable allowance	1,176	652
Deferred costs accumulated amortization	85,591	81,822
Accumulated amortization of acquired lease intangible assets	43,350	36,112
Accumulated accretion of acquired lease intangible liabilities	$ 16,689	$ 13,993
Preferred stock, par value per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	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	94,161,761	94,108,061
Exchangeable operating partnership units aggregate redemption value	$ 9,582	$ 9,833
Treasury stock, shares held at cost	414,541	425,246
Partnership Interest [Member]
Allowance for doubtful accounts receivable	$ 5,377	$ 4,523
Straight-line rent receivable allowance	1,176	652
Deferred costs accumulated amortization	85,591	81,882
Accumulated amortization of acquired lease intangible assets	43,350	36,112
Accumulated accretion of acquired lease intangible liabilities	$ 16,689	$ 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	94,161,761	94,108,061
Limited partner units, outstanding	154,170	154,170