Schedule - Summary of Real Estate and Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Real Estate and Accumulated Depreciation [Line Items]
Aggregate cost basis for federal income tax purposes	$ 3,303,200	$ 3,662,800
Initial Cost of Land	477,086
Initial Cost of Building & Improvements	1,791,286
Cost of Improvements Net of Retirements and Impairment Charges	1,031,642
Balance of Land and Land Held for Develop- ment	505,801
Balance of Building & Improvements and Construction in Progress	2,794,213
Accumulated Depreciation Balance	1,060,845	1,015,647	$ 1,061,051	$ 1,012,746
Current Encumbrance(1)	1,227,385
Real estate, federal income tax depreciated basis	2,380,800	2,660,700
Beaver Valley Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	10,822
Initial Cost of Building & Improvements	42,877
Cost of Improvements Net of Retirements and Impairment Charges	(17,239)
Balance of Land and Land Held for Develop- ment	4,233
Balance of Building & Improvements and Construction in Progress	32,227
Accumulated Depreciation Balance	$ 15,318
Date of Acquisition/ Construction	2002
Capital City Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 11,642
Initial Cost of Building & Improvements	65,575
Cost of Improvements Net of Retirements and Impairment Charges	35,267
Balance of Land and Land Held for Develop- ment	11,642
Balance of Building & Improvements and Construction in Progress	100,842
Accumulated Depreciation Balance	40,264
Current Encumbrance(1)	$ 61,107
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Cherry Hill Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 29,938
Initial Cost of Building & Improvements	185,611
Cost of Improvements Net of Retirements and Impairment Charges	256,826
Balance of Land and Land Held for Develop- ment	48,608
Balance of Building & Improvements and Construction in Progress	423,767
Accumulated Depreciation Balance	209,950
Current Encumbrance(1)	$ 287,124
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Crossroads Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 5,054
Initial Cost of Building & Improvements	22,496
Cost of Improvements Net of Retirements and Impairment Charges	6,798
Balance of Land and Land Held for Develop- ment	3,459
Balance of Building & Improvements and Construction in Progress	30,889
Accumulated Depreciation Balance	$ 11,256
Date of Acquisition/ Construction	2003
Cumberland Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 8,711
Initial Cost of Building & Improvements	43,889
Cost of Improvements Net of Retirements and Impairment Charges	29,738
Balance of Land and Land Held for Develop- ment	9,902
Balance of Building & Improvements and Construction in Progress	72,436
Accumulated Depreciation Balance	22,350
Current Encumbrance(1)	$ 46,588
Date of Acquisition/ Construction	2005
Life of Depre- ciation	40 years
Dartmouth Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 7,015
Initial Cost of Building & Improvements	28,328
Cost of Improvements Net of Retirements and Impairment Charges	35,016
Balance of Land and Land Held for Develop- ment	7,004
Balance of Building & Improvements and Construction in Progress	63,355
Accumulated Depreciation Balance	35,902
Current Encumbrance(1)	$ 62,460
Date of Acquisition/ Construction	1998
Life of Depre- ciation	40 years
Exton Square Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 21,460
Initial Cost of Building & Improvements	121,326
Cost of Improvements Net of Retirements and Impairment Charges	43,692
Balance of Land and Land Held for Develop- ment	27,875
Balance of Building & Improvements and Construction in Progress	158,603
Accumulated Depreciation Balance	48,842
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Francis Scott Key Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 9,786
Initial Cost of Building & Improvements	47,526
Cost of Improvements Net of Retirements and Impairment Charges	36,156
Balance of Land and Land Held for Develop- ment	9,440
Balance of Building & Improvements and Construction in Progress	84,028
Accumulated Depreciation Balance	35,118
Current Encumbrance(1)	$ 68,469
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Jacksonville Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 9,974
Initial Cost of Building & Improvements	47,802
Cost of Improvements Net of Retirements and Impairment Charges	28,113
Balance of Land and Land Held for Develop- ment	9,974
Balance of Building & Improvements and Construction in Progress	75,915
Accumulated Depreciation Balance	32,792
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Logan Valley Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 13,267
Initial Cost of Building & Improvements	68,449
Cost of Improvements Net of Retirements and Impairment Charges	26,097
Balance of Land and Land Held for Develop- ment	13,267
Balance of Building & Improvements and Construction in Progress	94,546
Accumulated Depreciation Balance	37,613
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Magnolia Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 9,279
Initial Cost of Building & Improvements	44,165
Cost of Improvements Net of Retirements and Impairment Charges	38,111
Balance of Land and Land Held for Develop- ment	15,893
Balance of Building & Improvements and Construction in Progress	75,662
Accumulated Depreciation Balance	41,994
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	1998
Life of Depre- ciation	40 years
Monroe Marketplace [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 1,177
Initial Cost of Building & Improvements	0
Cost of Improvements Net of Retirements and Impairment Charges	0
Balance of Land and Land Held for Develop- ment	1,177
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2006
Monroe Marketplace [Member]
Real Estate and Accumulated Depreciation [Line Items]
Balance of Building & Improvements and Construction in Progress	$ 0
Accumulated Depreciation Balance	$ 0
Life of Depre- ciation	10 years
Moorestown Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 11,368
Initial Cost of Building & Improvements	62,995
Cost of Improvements Net of Retirements and Impairment Charges	77,882
Balance of Land and Land Held for Develop- ment	11,368
Balance of Building & Improvements and Construction in Progress	140,877
Accumulated Depreciation Balance	51,616
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Patrick Henry Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 16,075
Initial Cost of Building & Improvements	86,643
Cost of Improvements Net of Retirements and Impairment Charges	49,655
Balance of Land and Land Held for Develop- ment	16,397
Balance of Building & Improvements and Construction in Progress	135,976
Accumulated Depreciation Balance	62,121
Current Encumbrance(1)	$ 94,029
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Plymouth Meeting Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 29,265
Initial Cost of Building & Improvements	58,388
Cost of Improvements Net of Retirements and Impairment Charges	97,084
Balance of Land and Land Held for Develop- ment	29,958
Balance of Building & Improvements and Construction in Progress	154,779
Accumulated Depreciation Balance	71,186
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
The Mall at Prince Georges [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 13,065
Initial Cost of Building & Improvements	57,686
Cost of Improvements Net of Retirements and Impairment Charges	38,918
Balance of Land and Land Held for Develop- ment	13,066
Balance of Building & Improvements and Construction in Progress	96,603
Accumulated Depreciation Balance	51,459
Current Encumbrance(1)	$ 150,000
Date of Acquisition/ Construction	1998
Life of Depre- ciation	40 years
Springfield Town Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 119,912
Initial Cost of Building & Improvements	353,551
Cost of Improvements Net of Retirements and Impairment Charges	11,802
Balance of Land and Land Held for Develop- ment	119,912
Balance of Building & Improvements and Construction in Progress	365,353
Accumulated Depreciation Balance	21,921
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2015
Life of Depre- ciation	40 years
Sunrise Plaza Land [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 395
Initial Cost of Building & Improvements	0
Cost of Improvements Net of Retirements and Impairment Charges	0
Balance of Land and Land Held for Develop- ment	395
Balance of Building & Improvements and Construction in Progress	0
Accumulated Depreciation Balance	0
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2005
Life of Depre- ciation	0 years
Swedes Square [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 189
Initial Cost of Building & Improvements	0
Cost of Improvements Net of Retirements and Impairment Charges	36
Balance of Land and Land Held for Develop- ment	225
Balance of Building & Improvements and Construction in Progress	0
Accumulated Depreciation Balance	0
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2004
Life of Depre- ciation	0 years
Valley Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 13,187
Initial Cost of Building & Improvements	60,658
Cost of Improvements Net of Retirements and Impairment Charges	36,001
Balance of Land and Land Held for Develop- ment	13,187
Balance of Building & Improvements and Construction in Progress	96,659
Accumulated Depreciation Balance	39,363
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Valley View Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 9,880
Initial Cost of Building & Improvements	46,817
Cost of Improvements Net of Retirements and Impairment Charges	22,679
Balance of Land and Land Held for Develop- ment	9,936
Balance of Building & Improvements and Construction in Progress	69,440
Accumulated Depreciation Balance	24,710
Current Encumbrance(1)	$ 29,169
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Viewmont Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 12,505
Initial Cost of Building & Improvements	61,519
Cost of Improvements Net of Retirements and Impairment Charges	34,812
Balance of Land and Land Held for Develop- ment	12,673
Balance of Building & Improvements and Construction in Progress	96,163
Accumulated Depreciation Balance	36,931
Current Encumbrance(1)	$ 57,000
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Willow Grove Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 26,748
Initial Cost of Building & Improvements	131,189
Cost of Improvements Net of Retirements and Impairment Charges	83,315
Balance of Land and Land Held for Develop- ment	36,188
Balance of Building & Improvements and Construction in Progress	205,064
Accumulated Depreciation Balance	88,976
Current Encumbrance(1)	$ 166,422
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Woodland Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 35,540
Initial Cost of Building & Improvements	124,504
Cost of Improvements Net of Retirements and Impairment Charges	64,660
Balance of Land and Land Held for Develop- ment	44,389
Balance of Building & Improvements and Construction in Progress	180,315
Accumulated Depreciation Balance	63,204
Current Encumbrance(1)	$ 128,880
Date of Acquisition/ Construction	2005
Life of Depre- ciation	40 years
Wyoming Valley Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 14,153
Initial Cost of Building & Improvements	73,035
Cost of Improvements Net of Retirements and Impairment Charges	26,738
Balance of Land and Land Held for Develop- ment	13,302
Balance of Building & Improvements and Construction in Progress	100,624
Accumulated Depreciation Balance	44,533
Current Encumbrance(1)	$ 76,137
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
White Clay Point [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 31,000
Initial Cost of Building & Improvements	11,803
Cost of Improvements Net of Retirements and Impairment Charges	(28,803)
Balance of Land and Land Held for Develop- ment	10,914
Balance of Building & Improvements and Construction in Progress	3,086
Accumulated Depreciation Balance	0
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2005
Life of Depre- ciation	0 years
Springhills [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 21,555
Initial Cost of Building & Improvements	9,827
Cost of Improvements Net of Retirements and Impairment Charges	(12,153)
Balance of Land and Land Held for Develop- ment	19,109
Balance of Building & Improvements and Construction in Progress	120
Accumulated Depreciation Balance	0
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2006
Life of Depre- ciation	0 years
Held-for-sale [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 15,876
Initial Cost of Building & Improvements	65,373
Cost of Improvements Net of Retirements and Impairment Charges	(10,441)
Balance of Land and Land Held for Develop- ment	7,692
Balance of Building & Improvements and Construction in Progress	63,116
Accumulated Depreciation Balance	26,574
Mortgage Loan [Member]
Real Estate and Accumulated Depreciation [Line Items]
Debt Issuance Costs, Net	$ 4,526	$ 4,200