Real Estate Acquisitions and Dispositions (Details) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended		1 Months Ended		1 Months Ended	3 Months Ended	6 Months Ended				3 Months Ended
	Dec. 31, 2011 property	Dec. 31, 2011	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	May 31, 2012 The Domain in Austin, TX property	Jun. 04, 2012 Outlet centers Destin, Florida sqft	Jun. 30, 2011 Other Retail Property property	Mar. 31, 2012 Other Retail Property property	Jun. 30, 2011 Other Retail Property property	Mar. 22, 2012 The Mills acquisition property	Mar. 14, 2012 Klepierre	Jan. 06, 2012 Del Amo Fashion Center	Sep. 30, 2011 King of Prussia	Jun. 30, 2012 King of Prussia	Aug. 25, 2011 King of Prussia
Real Estate Acquisitions and Dispositions
Ownership interests acquired (as a percent)							50.00%					28.70%
Area of lifestyle center acquired (in square feet)							465,000
Cost of acquisition including assumption of debt							$ 70,500,000				$ 1,500,000,000	$ 2,000,000,000
Number of properties sold						2		1	1	2
Proceeds from sale or disposal of real estate assets								134,000,000
Gain upon acquisition of controlling interests, sale or disposal of assets and interests in unconsolidated entities, and impairment charge on investment in unconsolidated entities, net			14,349,000	494,837,000	13,765,000	12,100,000		6,600,000		7,200,000
Number of joint ventures in which additional interest is acquired											26
Additional Business Acquisition Percentage of Ownership Acquired													25.00%			83.75%
Aggregate carrying value of consolidated properties disposed of									115,000,000
Debt obligation related to consolidated properties disposed of									115,000,000
Joint venture ownership percentage	50.00%	50.00%
Initial Investment Percentage of Business Acquired	100.00%	100.00%
Number of consolidated properties received in distribution	6
Gain due to acquisition of controlling interest		168,300,000												82,900,000
Cumulative Investment Ownership Percentage (as a percent)																96.10%
Mortgage indebtedness assumed															$ 160,100,000