Real Estate Activities (Dispositions of Assets for Discontinued Operations) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013 Phillipsburg Mall [Member] 2014 [Member] Mall [Member]	Dec. 31, 2013 Phillipsburg Mall [Member] 2014 [Member] Mall [Member]	Mar. 31, 2013 Paxton Towne Centre [Member] 2014 [Member] Power Center [Member]	Dec. 31, 2013 Paxton Towne Centre [Member] 2014 [Member] Power Center [Member]	Mar. 31, 2013 Orlando Fashion Square [Member] 2014 [Member] Mall [Member]	Dec. 31, 2013 Orlando Fashion Square [Member] 2014 [Member] Mall [Member]	Mar. 31, 2013 Commons at Magnolia [Member] 2014 [Member] Power Center [Member]	Dec. 31, 2013 Commons at Magnolia [Member] 2014 [Member] Power Center [Member]	Mar. 31, 2013 Christiana Center [Member] 2014 [Member] Power Center [Member]	Dec. 31, 2013 Christiana Center [Member] 2014 [Member] Power Center [Member]	Mar. 31, 2013 Chambersburg Mall [Member] 2014 [Member] Mall [Member]	Dec. 31, 2012 Voorhees Town Center [Member] 2011 Activity [Member] Condominium interest in mall [Member ]	Dec. 31, 2012 Pitney Road Plaza [Member] 2011 Activity [Member] Parcel and land improvements [Member]	Dec. 31, 2012 New River Valley Mall [Member] 2011 Activity [Member] Unimproved land parcel [Member]
Disposals [Line Items]
Capitalization Rate	9.80%			6.90%		9.80%		8.90%		6.50%
Sale Price	$ 11.5		$ 76.8		$ 35.0		$ 12.3		$ 75.0		$ 8.5	$ 5.9	$ 1.4	$ 0.2
Gain/ (Loss)		$ 0	$ 32.7		$ 0.7		$ 4.3		$ 40.8			$ 0.7	$ 0.7	$ 0.1