Schedule - Summary of Real Estate and Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate and Accumulated Depreciation [Line Items]
Aggregate cost basis for federal income tax purposes	$ 3,302,700	$ 3,174,700
Initial Cost of Land	411,264
Initial Cost of Building & Improvements	1,701,207
Cost of Improvements Net of Retirements and Impairment Charges	1,072,123
Balance of Land and Land Held for Develop- ment	465,194
Balance of Building & Improvements and Construction in Progress	2,719,400
Accumulated Depreciation Balance	1,118,582	1,111,007	$ 1,060,845	$ 1,015,647
Current Encumbrance(1)	1,050,970
Real estate, federal income tax depreciated basis	2,353,400	2,284,000
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	58,360
Balance of Land and Land Held for Develop- ment	11,690
Balance of Building & Improvements and Construction in Progress	123,887
Accumulated Depreciation Balance	46,878
Current Encumbrance(1)	$ 58,792
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	261,423
Balance of Land and Land Held for Develop- ment	48,608
Balance of Building & Improvements and Construction in Progress	428,366
Accumulated Depreciation Balance	244,194
Current Encumbrance(1)	$ 275,117
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	31,335
Balance of Land and Land Held for Develop- ment	9,842
Balance of Building & Improvements and Construction in Progress	74,093
Accumulated Depreciation Balance	28,301
Current Encumbrance(1)	$ 43,759
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	45,641
Balance of Land and Land Held for Develop- ment	7,004
Balance of Building & Improvements and Construction in Progress	73,980
Accumulated Depreciation Balance	39,767
Current Encumbrance(1)	$ 59,735
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	(74,471)
Balance of Land and Land Held for Develop- ment	25,198
Balance of Building & Improvements and Construction in Progress	43,117
Accumulated Depreciation Balance	11,335
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	40,810
Balance of Land and Land Held for Develop- ment	9,440
Balance of Building & Improvements and Construction in Progress	88,682
Accumulated Depreciation Balance	40,386
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	32,036
Balance of Land and Land Held for Develop- ment	9,974
Balance of Building & Improvements and Construction in Progress	79,838
Accumulated Depreciation Balance	37,361
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	53,989
Balance of Land and Land Held for Develop- ment	15,642
Balance of Building & Improvements and Construction in Progress	91,791
Accumulated Depreciation Balance	46,119
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	106,206
Balance of Land and Land Held for Develop- ment	16,010
Balance of Building & Improvements and Construction in Progress	164,559
Accumulated Depreciation Balance	65,068
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	53,099
Balance of Land and Land Held for Develop- ment	16,397
Balance of Building & Improvements and Construction in Progress	139,420
Accumulated Depreciation Balance	68,664
Current Encumbrance(1)	$ 90,692
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	123,072
Balance of Land and Land Held for Develop- ment	30,790
Balance of Building & Improvements and Construction in Progress	179,935
Accumulated Depreciation Balance	87,725
Current Encumbrance(1)	$ 0
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
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	69,994
Balance of Land and Land Held for Develop- ment	13,066
Balance of Building & Improvements and Construction in Progress	127,679
Accumulated Depreciation Balance	58,120
Current Encumbrance(1)	$ 0
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	20,675
Balance of Land and Land Held for Develop- ment	119,912
Balance of Building & Improvements and Construction in Progress	374,226
Accumulated Depreciation Balance	50,639
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	(29)
Balance of Land and Land Held for Develop- ment	366
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	66,193
Balance of Land and Land Held for Develop- ment	24,914
Balance of Building & Improvements and Construction in Progress	115,123
Accumulated Depreciation Balance	44,791
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	(18,355)
Balance of Land and Land Held for Develop- ment	4,682
Balance of Building & Improvements and Construction in Progress	33,659
Accumulated Depreciation Balance	11,255
Current Encumbrance(1)	$ 28,044
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	47,395
Balance of Land and Land Held for Develop- ment	12,606
Balance of Building & Improvements and Construction in Progress	108,813
Accumulated Depreciation Balance	45,283
Current Encumbrance(1)	$ 67,185
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	86,747
Balance of Land and Land Held for Develop- ment	36,295
Balance of Building & Improvements and Construction in Progress	208,389
Accumulated Depreciation Balance	98,194
Current Encumbrance(1)	$ 159,900
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	95,827
Balance of Land and Land Held for Develop- ment	44,900
Balance of Building & Improvements and Construction in Progress	210,971
Accumulated Depreciation Balance	71,806
Current Encumbrance(1)	$ 125,520
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	(27,860)
Balance of Land and Land Held for Develop- ment	6,456
Balance of Building & Improvements and Construction in Progress	52,872
Accumulated Depreciation Balance	22,696
Current Encumbrance(1)	$ 73,757
Date of Acquisition/ Construction	2003
Life of Depre- ciation	40 years
White Clay Point [Member]
Real Estate and Accumulated Depreciation [Line Items]
Life of Depre- ciation	0 years
Springhills [Member]
Real Estate and Accumulated Depreciation [Line Items]
Life of Depre- ciation	0 years
Mortgage Loan [Member]
Real Estate and Accumulated Depreciation [Line Items]
Debt Issuance Costs, Net	$ 3,064	$ 3,400