Real Estate Activities (Impairment of Assets) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2011
Impairment Of Assets [Line Items]
Impairment of Assets	$ 62,603	$ 140,318	$ 19,695
White Clay Point [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	20,786
Washington Crown Center [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	18,055
Beaver Valley Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	14,117
Crossroads Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	9,038
Voorhees office building [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	607
Gadsden Mall, New River Valley Mall and Wiregrass Commons Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	63,904
Voorhees Town Center [Member]
Impairment Of Assets [Line Items]
Impairment of Assets		39,242
Lycoming Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	$ 28,345
Uniontown Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets		7,394
Palmer Park Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets		1,383
Nittany Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets		0	15,495
South Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets		0	1,300
North Hanover Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets		0	$ 2,900	$ 24,100
Other [Member]
Impairment Of Assets [Line Items]
Impairment of Assets		$ 50