Investments in Partially Owned Entities (Urban Edge Properties and PREIT Associates L.P.) (Details) $ / shares in Units, ft² in Thousands			9 Months Ended
	Mar. 31, 2015 USD ($) ft² $ / shares shares	Jan. 15, 2015 shares	Sep. 30, 2015 USD ($) $ / shares	Sep. 30, 2014 USD ($)
Schedule Of Equity Method Investments [Line Items]
Cash Proceeds from sale of real estate			$ 10,731,000
Operating Partnership Units Value			$ 80,000,000	$ 0
Pennsylavenia 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			$ 19.83
Equity Method Investment fair Value			$ 123,938,000
Excess of investee's carrying amount over fair value			14,327,000
Excess of investee's carrying amount over equity in net assets			$ 65,681,000
Retail Springfield Mall [Member] | Retail Segment Regional Malls [Member] | Pennsylavenia Real Estate Investment Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Operating Partnership Units Received From Buyer | shares	6,250,000
Square Footage Of Real Estate Property | ft²	1,350
Gross proceeds from sale of real estate	$ 485,313,000
Cash Proceeds from sale of real estate	340,000,000
Operating Partnership Units Value	$ 145,313,000
Operating Partnership Unis Value Per Unit | $ / shares	$ 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
Equity method ownership percentage		5.40%
Closing share price (in dollars per share) | $ / shares			$ 21.59
Equity Method Investment fair Value			$ 123,434,000
Excess of investee's fair value over carrying amount			$ 98,033,000
Urban Edge Properties [Member] | Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Duration Of Administrative Services		2 years