Schedule - Summary of Real Estate and Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 501,924
Initial Cost of Building & Improvements	1,883,795
Cost of Improvements Net of Retirements and Impairment Charges	982,170
Balance of Land and Land Held for Develop- ment	519,903
Balance of Building & Improvements and Construction in Progress	2,847,986
Accumulated Depreciation Balance	1,015,647	$ 1,061,051	$ 1,012,746	$ 907,928
Current Encumbrance	$ 1,325,495
Date of Acquisition/ Construction	2003
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	21,752
Balance of Land and Land Held for Develop- ment	10,550
Balance of Building & Improvements and Construction in Progress	64,901
Accumulated Depreciation Balance	33,555
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2002
Life of Depre- ciation	30 years
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	31,069
Balance of Land and Land Held for Develop- ment	11,642
Balance of Building & Improvements and Construction in Progress	96,644
Accumulated Depreciation Balance	37,284
Current Encumbrance	$ 62,165
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	257,178
Balance of Land and Land Held for Develop- ment	48,608
Balance of Building & Improvements and Construction in Progress	424,119
Accumulated Depreciation Balance	185,049
Current Encumbrance	$ 292,786
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	21,899
Balance of Land and Land Held for Develop- ment	5,627
Balance of Building & Improvements and Construction in Progress	43,822
Accumulated Depreciation Balance	16,811
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
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	18,492
Balance of Land and Land Held for Develop- ment	9,842
Balance of Building & Improvements and Construction in Progress	61,250
Accumulated Depreciation Balance	19,560
Current Encumbrance	$ 47,905
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	32,479
Balance of Land and Land Held for Develop- ment	7,004
Balance of Building & Improvements and Construction in Progress	60,818
Accumulated Depreciation Balance	33,870
Current Encumbrance	$ 63,736
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	18,940
Balance of Land and Land Held for Develop- ment	25,209
Balance of Building & Improvements and Construction in Progress	136,517
Accumulated Depreciation Balance	44,755
Current Encumbrance	$ 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	33,037
Balance of Land and Land Held for Develop- ment	9,639
Balance of Building & Improvements and Construction in Progress	80,710
Accumulated Depreciation Balance	31,647
Current Encumbrance	$ 68,469
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Gadsden Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 8,842
Initial Cost of Building & Improvements	42,681
Cost of Improvements Net of Retirements and Impairment Charges	(29,480)
Balance of Land and Land Held for Develop- ment	1,544
Balance of Building & Improvements and Construction in Progress	20,499
Accumulated Depreciation Balance	7,652
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2005
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	26,691
Balance of Land and Land Held for Develop- ment	9,974
Balance of Building & Improvements and Construction in Progress	74,493
Accumulated Depreciation Balance	29,963
Current Encumbrance	$ 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	22,656
Balance of Land and Land Held for Develop- ment	13,267
Balance of Building & Improvements and Construction in Progress	91,105
Accumulated Depreciation Balance	34,303
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Lycoming Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 10,274
Initial Cost of Building & Improvements	43,440
Cost of Improvements Net of Retirements and Impairment Charges	(13,364)
Balance of Land and Land Held for Develop- ment	3,468
Balance of Building & Improvements and Construction in Progress	36,882
Accumulated Depreciation Balance	15,781
Current Encumbrance	33,035
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	36,655
Balance of Land and Land Held for Develop- ment	15,204
Balance of Building & Improvements and Construction in Progress	74,895
Accumulated Depreciation Balance	39,537
Current Encumbrance	$ 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	$ 2,430
Initial Cost of Building & Improvements	0
Cost of Improvements Net of Retirements and Impairment Charges	265
Balance of Land and Land Held for Develop- ment	2,430
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2006
Monroe Marketplace [Member]
Real Estate and Accumulated Depreciation [Line Items]
Balance of Building & Improvements and Construction in Progress	$ 265
Accumulated Depreciation Balance	$ 86
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	70,189
Balance of Land and Land Held for Develop- ment	11,368
Balance of Building & Improvements and Construction in Progress	133,184
Accumulated Depreciation Balance	44,234
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
New River Valley Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 4,751
Initial Cost of Building & Improvements	22,808
Cost of Improvements Net of Retirements and Impairment Charges	5,505
Balance of Land and Land Held for Develop- ment	727
Balance of Building & Improvements and Construction in Progress	32,337
Accumulated Depreciation Balance	23,254
Current Encumbrance	$ 28,050
Date of Acquisition/ Construction	2003
Palmer Park Mall [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 3,747
Initial Cost of Building & Improvements	18,805
Cost of Improvements Net of Retirements and Impairment Charges	2,153
Balance of Land and Land Held for Develop- ment	3,371
Balance of Building & Improvements and Construction in Progress	21,334
Accumulated Depreciation Balance	6,829
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2003
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	43,134
Balance of Land and Land Held for Develop- ment	16,397
Balance of Building & Improvements and Construction in Progress	129,455
Accumulated Depreciation Balance	58,362
Current Encumbrance	$ 95,579
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Pitney Road Plaza Land [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 905
Initial Cost of Building & Improvements	0
Cost of Improvements Net of Retirements and Impairment Charges	(905)
Balance of Land and Land Held for Develop- ment	0
Balance of Building & Improvements and Construction in Progress	0
Accumulated Depreciation Balance	0
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2006
Life of Depre- ciation	0 years
Pitney Road Plaza [Member]
Real Estate and Accumulated Depreciation [Line Items]
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	90,343
Balance of Land and Land Held for Develop- ment	29,947
Balance of Building & Improvements and Construction in Progress	148,049
Accumulated Depreciation Balance	61,885
Current Encumbrance	$ 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	33,199
Balance of Land and Land Held for Develop- ment	13,066
Balance of Building & Improvements and Construction in Progress	90,884
Accumulated Depreciation Balance	48,364
Current Encumbrance	$ 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	1,521
Balance of Land and Land Held for Develop- ment	119,912
Balance of Building & Improvements and Construction in Progress	355,072
Accumulated Depreciation Balance	8,545
Current Encumbrance	$ 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	$ 1,739
Initial Cost of Building & Improvements	0
Cost of Improvements Net of Retirements and Impairment Charges	690
Balance of Land and Land Held for Develop- ment	837
Balance of Building & Improvements and Construction in Progress	1,592
Accumulated Depreciation Balance	0
Current Encumbrance	$ 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	30
Balance of Land and Land Held for Develop- ment	219
Balance of Building & Improvements and Construction in Progress	0
Accumulated Depreciation Balance	0
Current Encumbrance	$ 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	28,641
Balance of Land and Land Held for Develop- ment	13,187
Balance of Building & Improvements and Construction in Progress	89,299
Accumulated Depreciation Balance	34,843
Current Encumbrance	$ 79,268
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	22,312
Balance of Land and Land Held for Develop- ment	9,936
Balance of Building & Improvements and Construction in Progress	69,073
Accumulated Depreciation Balance	22,841
Current Encumbrance	$ 29,678
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	27,919
Balance of Land and Land Held for Develop- ment	12,606
Balance of Building & Improvements and Construction in Progress	89,337
Accumulated Depreciation Balance	32,920
Current Encumbrance	$ 48,000
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Voorhees Town Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 0
Initial Cost of Building & Improvements	0
Cost of Improvements Net of Retirements and Impairment Charges	4,491
Balance of Land and Land Held for Develop- ment	401
Balance of Building & Improvements and Construction in Progress	4,090
Accumulated Depreciation Balance	141
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	20 years
Washington Crown Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 5,460
Initial Cost of Building & Improvements	27,136
Cost of Improvements Net of Retirements and Impairment Charges	19,463
Balance of Land and Land Held for Develop- ment	5,282
Balance of Building & Improvements and Construction in Progress	46,777
Accumulated Depreciation Balance	18,550
Current Encumbrance	$ 0
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	80,762
Balance of Land and Land Held for Develop- ment	36,188
Balance of Building & Improvements and Construction in Progress	202,511
Accumulated Depreciation Balance	80,708
Current Encumbrance	$ 169,499
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Wiregrass Commons [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 5,103
Initial Cost of Building & Improvements	28,758
Cost of Improvements Net of Retirements and Impairment Charges	6,099
Balance of Land and Land Held for Develop- ment	5,592
Balance of Building & Improvements and Construction in Progress	34,368
Accumulated Depreciation Balance	10,338
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2003
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	33,757
Balance of Land and Land Held for Develop- ment	17,577
Balance of Building & Improvements and Construction in Progress	176,224
Accumulated Depreciation Balance	57,033
Current Encumbrance	$ 141,185
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	25,681
Balance of Land and Land Held for Develop- ment	13,302
Balance of Building & Improvements and Construction in Progress	99,567
Accumulated Depreciation Balance	40,801
Current Encumbrance	$ 77,225
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
Chestnut Street Retail [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 1,036
Initial Cost of Building & Improvements	5,152
Cost of Improvements Net of Retirements and Impairment Charges	0
Balance of Land and Land Held for Develop- ment	1,036
Balance of Building & Improvements and Construction in Progress	5,152
Accumulated Depreciation Balance	515
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2014
Walnut Street Retail [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 3,483
Initial Cost of Building & Improvements	10,556
Cost of Improvements Net of Retirements and Impairment Charges	3,785
Balance of Land and Land Held for Develop- ment	3,483
Balance of Building & Improvements and Construction in Progress	14,341
Accumulated Depreciation Balance	1,057
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2014
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	(8,017)
Balance of Land and Land Held for Develop- ment	31,612
Balance of Building & Improvements and Construction in Progress	3,174
Accumulated Depreciation Balance	0
Current Encumbrance	$ 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	19,070
Balance of Building & Improvements and Construction in Progress	159
Accumulated Depreciation Balance	0
Current Encumbrance	$ 0
Date of Acquisition/ Construction	2006
Life of Depre- ciation	0 years
Discontinued Operations, Held-for-sale [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost of Land	$ 37,236
Initial Cost of Building & Improvements	172,200
Cost of Improvements Net of Retirements and Impairment Charges	(25,302)
Balance of Land and Land Held for Develop- ment	19,221
Balance of Building & Improvements and Construction in Progress	164,913
Accumulated Depreciation Balance	65,426
Current Encumbrance	$ 61,085