Financing Activity (Mortgage Loan Activity) (Detail) (USD $)		12 Months Ended	1 Months Ended						1 Months Ended	12 Months Ended		12 Months Ended		1 Months Ended				12 Months Ended	1 Months Ended		12 Months Ended		12 Months Ended					12 Months Ended
	Dec. 31, 2013 Francis Scott Key Mall [Member] Mortgages [Member]	Dec. 31, 2013 Francis Scott Key Mall [Member] Mortgages [Member] LIBOR [Member]	Feb. 28, 2013 Lycoming Mall [Member]	Mar. 31, 2010 Lycoming Mall [Member]	Oct. 31, 2009 Lycoming Mall [Member]	Sep. 30, 2009 Lycoming Mall [Member]	Dec. 31, 2013 Lycoming Mall [Member] Mortgages [Member]	Feb. 28, 2013 Lycoming Mall [Member] Mortgages [Member]	Feb. 28, 2013 Lycoming Mall [Member] Mortgages [Member] LIBOR [Member]	Dec. 31, 2013 Lycoming Mall [Member] Mortgages [Member] LIBOR [Member]	Dec. 31, 2013 Viewmont Mall [Member] Mortgages [Member]	Dec. 31, 2013 Viewmont Mall [Member] Mortgages [Member] LIBOR [Member]	Dec. 31, 2013 Dartmouth Mall [Member] Mortgages [Member]	Sep. 30, 2013 Logan Valley Mall [Member]	Sep. 30, 2011 Logan Valley Mall [Member]	Aug. 31, 2011 Logan Valley Mall [Member]	Dec. 31, 2013 Logan Valley Mall [Member] Mortgages [Member]	Dec. 31, 2013 Logan Valley Mall [Member] Mortgages [Member] LIBOR [Member]	Sep. 30, 2013 Wyoming Valley Mall [Member]	Dec. 31, 2013 Wyoming Valley Mall [Member] Mortgages [Member]	Dec. 31, 2013 New River Valley Mall [Member]	Dec. 31, 2013 New River Valley Mall [Member] Mortgages [Member]	Dec. 31, 2013 New River Valley Mall [Member] Mortgages [Member] LIBOR [Member]	Dec. 31, 2013 Capital City Mall [Member] Mortgages [Member]	Dec. 31, 2013 Christiana Center [Member] Mortgages [Member]	Sep. 30, 2013 Christiana Center [Member] Mortgages [Member]	Dec. 31, 2013 Cumberland Mall [Member] Mortgages [Member]	Dec. 31, 2013 Cherry Hill Mall [Member]	Dec. 31, 2013 Cherry Hill Mall [Member] Mortgages [Member]
Mortgage Loan Activity [Line Items]
Amount Financed or Extended (in millions of dollars)	$ 62,600,000						$ 35,500,000	$ 33,400,000			$ 48,000,000		$ 67,000,000				$ 51,000,000			$ 78,000,000		$ 28,100,000		$ 65,800,000	$ 50,000,000		$ 52,000,000		$ 300,000,000
Stated Interest Rate		2.60%							2.75%	2.75%		2.60%						2.10%					3.00%
Stated Interest Rate													3.97%							5.17%				5.30%	4.64%		4.40%		3.90%
Potential increase	7,900,000
Proceeds from secured mortgage loans			2,100,000	2,500,000	5,000,000	28,000,000										68,000,000
Repayment Of mortgage secured loan														12,000,000	5,000,000				65,000,000
Mortgage term loan for interest only payments																					5 years							2 years
Amortization schedule																					25 years
Mortgage assumed by buyer																										$ 49,200,000