Acquisitions and Discontinued Operations Acquisitions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			3 Months Ended		3 Months Ended		3 Months Ended			3 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2012 Dakota Square Mall [Member]	May 16, 2012 Dakota Square Mall [Member]	Sep. 30, 2012 Outlet Shoppes at Gettysburg [Member]	Apr. 17, 2012 Outlet Shoppes at Gettysburg [Member]	Sep. 30, 2012 Outlet Shoppes at El Paso and El Paso Outparcels [Member]	Apr. 20, 2012 Outlet Shoppes at El Paso and El Paso Outparcels [Member]	Apr. 20, 2012 El Paso Outlet Outparcels, LLC [Member]	Sep. 30, 2012 Outlet Shoppes at El Paso [Member]	Apr. 20, 2012 Outlet Shoppes at El Paso [Member]	Mar. 31, 2012 Outlet Shoppes at El Paso [Member]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Purchase Price					$ 91,475
Payments to Acquire Real Estate Held-for-investment					32,474				35,456			31,592
Debt Conversion, Converted Instrument, Amount						4,522
Noncash Or Part Noncash Acquisition Debt Assumed, Company Share						20,315
Debt Instrument, Interest Rate, Stated Percentage					6.23%		5.87%					7.06%
Debt Instrument, Maturity Date				Nov. 30, 2016		Feb. 28, 2016					Dec. 31, 2017
Percentage of Equity Interest in Real Estate Property							50.00%			50.00%		75.00%
Fair value of real estate investment	27,043						24,837					116,775
Business Acquisition, Cost of Acquired Entity, Transaction Costs				272
Business Acquisition Mortgage Notes Payable Fair Value Interest Rate Assumed Percentage					4.75%							4.75%
Receivable with Imputed Interest, Face Amount													9,150
Land	872,171	851,303			4,749		20,915					12,846
Buildings and improvements	7,020,344	6,777,776			84,086		19,750					92,305
Tenant Improvements					2,426		2,134					3,845
Above-market leases					2,233		1,097					2,912
In-place leases					12,489		9,282					15,629
Investments in unconsolidated affiliates	302,635	304,710								3,864
Total assets	6,890,316	6,719,428	7,422,495		105,983		53,178		131,401
Below-market leases					11,468		(3,503)		(6,926)
Noncash or Part Noncash Acquisition, Debt Assumed	177,296			59,001		(40,631)		(66,924)
Partners' Capital Attributable to Noncontrolling Interest						4,522		(14,395)
Debt premium					(3,040)				(7,700)
Business Acquisition, Purchase Price Allocation, Mortgage Notes Payable Premium, Company share												5,775
Assets, Net					32,474		4,522		35,456
Business acquisition cost, cash paid less repayment of mezzanine loan												$ 28,594