Real Estate Activities (Dispositions of Assets for Discontinued Operations) (Detail) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Feb. 29, 2016	Jan. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Parcel And Land Improvements [Member]
Disposals [Line Items]
Sale Price			$ 5.1	$ 9.9
Gain/ (Loss)			$ 1.8
Uniontown Mall [Member] | Mall [Member]
Disposals [Line Items]
Capitalization Rate			17.50%
Sale Price			$ 23.0
Gain/ (Loss)			$ 0.0
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)					$ 0.0
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)					$ 0.0
Voorhees Town Center [Member] | Mall [Member]
Disposals [Line Items]
Capitalization Rate			10.30%
Sale Price			$ 13.4
Gain/ (Loss)			$ 0.0
Subsequent Event [Member] | Parcel And Land Improvements [Member]
Disposals [Line Items]
Sale Price		$ 2.0
Subsequent Event [Member] | Palmer Park Mall [Member] | Mall [Member]
Disposals [Line Items]
Gain/ (Loss)	$ 0.0