Real Estate Activities (Narrative) (Detail) - USD ($)		1 Months Ended			3 Months Ended											12 Months Ended
	Jul. 28, 2014	Jul. 31, 2014	Sep. 30, 2013	Apr. 30, 2013	Dec. 31, 2015		Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	[1]	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2011
Real Estate Properties [Line Items]
Impairment Of Assets																$ 140,318,000	$ 19,695,000	$ 29,966,000
Gain or loss on sale of real estate					$ 13,100,000		$ 12,400,000									259,000	1,774,000
Income recognized from grant					$ (39,910,000)	[1]		$ (32,340,000)	$ (30,924,000)	$ (13,509,000)	$ 18,458,000		$ (859,000)	$ (23,325,000)	$ (8,104,000)	(116,683,000)	(13,830,000)	35,859,000
Land purchase contracts																100,000
Repayments of Secured Debt																272,650,000	76,784,000	403,691,000
Nittany Mall [Member]
Real Estate Properties [Line Items]
Impairment Of Assets																0	$ 15,495,000
Capitalization Rate																	16.20%
The Gallery at Market East [Member]
Real Estate Properties [Line Items]
Payments to acquire buildings				$ 59,600,000
Capitalization Rate				5.70%
Chambersburg Mall [Member]
Real Estate Properties [Line Items]
Impairment Of Assets																	$ 0	23,662,000
North Hanover Mall [Member]
Real Estate Properties [Line Items]
Impairment Of Assets																0	$ 2,900,000	$ 6,304,000	$ 24,100,000
Capitalization Rate																	11.00%
Voorhees Town Center [Member]
Real Estate Properties [Line Items]
Impairment Of Assets																39,242,000
Proceeds from sale of building			$ 10,500,000
Gain (Loss) on sale of building			$ 0
The Gallery at Market East [Member]
Real Estate Properties [Line Items]
Real Estate Property Sales Price	$ 106,900,000	$ 106,800,000
Proceeds from Sale of Real Estate								104,000,000
Repayments of Secured Debt		$ 25,800,000
Repayments of Unsecured Debt								$ 50,000,000
Parcel And Land Improvements [Member]
Real Estate Properties [Line Items]
Sale Price																5,100,000	$ 9,900,000
Gain/ (Loss)																1,800,000
Land, Buildings and Improvements [Member]
Real Estate Properties [Line Items]
Gain/ (Loss)																$ 700,000	$ 600,000

[1] Fourth Quarter revenue includes a significant portion of annual percentage rent as most percentage rent minimum sales levels are met in the fourth quarter.