Investments in Partially Owned Entities (Urban Edge Properties and PREIT Associates L.P.) (Details) $ / shares in Units, ft² in Thousands	Mar. 31, 2015 USD ($) ft² $ / shares shares	Jan. 15, 2015 shares	Mar. 02, 2014 USD ($) ft² $ / shares shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Schedule Of Equity Method Investments [Line Items]
Operating Partnership Units Value				$ 80,000,000	$ 0	$ 0
Pennsylvania Real Estate Investment Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method ownership percentage	8.10%			8.10%
Closing share price (in dollars per share) | $ / shares				$ 21.87
Equity Method Investment fair Value				$ 136,688,000
Excess of investee's fair value over carrying amount				3,313,000
Excess of investee's carrying amount over equity in net assets				$ 65,404,000
Springfield Mall [Member] | Pennsylvania Real Estate Investment Trust [Member] | Discontinued Operations, Disposed of by Sale [Member]
Schedule Of Equity Method Investments [Line Items]
Operating Partnership Units Received From Buyer | shares	6,250,000		6,250,000
Square Footage Of Real Estate Property | ft²	1,350		1,350
Gross proceeds from sale of real estate	$ 485,313,000		$ 485,313,000
Cash Proceeds from sale of real estate	340,000,000		340,000,000
Operating Partnership Units Value	$ 145,313,000		$ 145,313,000
Operating Partnership Unis Value Per Unit | $ / shares	$ 23.25		$ 23.25
Payments for tenant improvements and allowances	$ 19,000,000
Urban Edge Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Operating Partnership Units Received From Buyer | shares		5,717,184
Closing share price (in dollars per share) | $ / shares				$ 23.45
Equity Method Investment fair Value				$ 134,068,000
Excess of investee's fair value over carrying amount				$ 108,717,000
Urban Edge Properties [Member] | Discontinued Operations, Disposed of by Sale [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method ownership percentage		5.40%
Urban Edge Properties [Member] | Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Duration Of Administrative Services		2 years
Urban Edge Properties [Member] | Maximum [Member] | Discontinued Operations, Disposed of by Sale [Member]
Schedule Of Equity Method Investments [Line Items]
Duration Of Administrative Services		2 years