Real Estate Activities (Dispositions of Assets for Discontinued Operations) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
South Mall [Member] | Mall [Member]
Disposals [Line Items]
Capitalization Rate	10.10%
Sale Price	$ 23.6
Gain/ (Loss)	0.2
The Gallery at Market East [Member] | Mall [Member]
Disposals [Line Items]
Capitalization Rate	5.10%
Sale Price	106.8
Gain/ (Loss)	(0.6)
North Hanover Mall and Nittany Mall Combined [Member] | Mall [Member]
Disposals [Line Items]
Sale Price	32.3
Gain/ (Loss)	(0.1)
Phillipsburg Mall [Member] | Mall [Member]
Disposals [Line Items]
Capitalization Rate		9.80%
Sale Price		11.5
Gain/ (Loss)		0
Paxton Towne Centre [Member] | Power Center [Member]
Disposals [Line Items]
Capitalization Rate		6.90%
Sale Price		76.8
Gain/ (Loss)		32.7
Orlando Fashion Square [Member] | Mall [Member]
Disposals [Line Items]
Capitalization Rate		9.80%
Sale Price		35.0
Gain/ (Loss)		0.7
Commons at Magnolia [Member] | Power Center [Member]
Disposals [Line Items]
Capitalization Rate		8.90%
Sale Price		12.3
Gain/ (Loss)		4.3
Christiana Center [Member] | Power Center [Member]
Disposals [Line Items]
Capitalization Rate		6.50%
Sale Price		75.0
Gain/ (Loss)		40.8
Chambersburg Mall [Member] | Mall [Member]
Disposals [Line Items]
Sale Price		8.5
Gain/ (Loss)		$ 0