Real Estate Activities (Impairment of Assets) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impairment Of Assets [Line Items]
Impairment of Assets	$ 55,793	$ 62,603	$ 140,318
Logan Valley Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	38,720
Valley View Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	$ 15,521
Fair Value Input Terminal Capitalization Rate	12.00%
Springhills [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	$ 1,275
White Clay Point [Member]
Impairment Of Assets [Line Items]
Impairment of Assets		20,786
Sunrise Plaza Land [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	226
Beaver Valley Mall [Member]
Impairment Of Assets [Line Items]
Impairment of Assets		18,055
Washington Crown Center [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
Other [Member]
Impairment Of Assets [Line Items]
Impairment of Assets	$ 51		$ 50