Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Allowance for doubtful accounts receivable	$ 4,523	$ 3,922
General partner units, outstanding	94,108,061	92,333,000
Limited Partners' Capital Account, Units Outstanding	154,170	165,796
Parent Company [Member]
Preferred stock, shares authorized	30,000,000	30,000,000
Preferred units of Series 3-5, units issued	13,000,000
Common stock, par value per share	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Exchangeable operating partnership units aggregate redemption value	9,833	7,676
Treasury stock, shares held at cost	425,246	373,042
Partnership Interest [Member]
Allowance for doubtful accounts receivable	4,523	3,922
Straight-line rent receivable allowance	652	547
Deferred costs accumulated amortization	81,822	73,231
Accumulated amortization of acquired lease intangible assets	36,112	25,591
Accumulated accretion of acquired lease intangible liabilities	$ 13,993	$ 10,102
Preferred stock, par value per share	$ 0.01	$ 0.01
Preferred units of Series 3-5, units issued	13,000,000	13,000,000
Preferred units of Series 3-5, units outstanding	13,000,000	13,000,000
Preferred stock, liquidation preferences per share	$ 25	$ 25
Common stock, shares issued	94,108,061	92,333,161
Limited Partners' Capital Account, Units Outstanding	154,170	165,796