Significant Acquisitions and Dispositions Significant Acquisitions and Dispositions (Calculation of Gain (Loss) on Acquisition) (Details) (USD $)		0 Months Ended	3 Months Ended	0 Months Ended	12 Months Ended
	Apr. 01, 2009	Apr. 01, 2009 Consolidation of Retail Joint Ventures [Member] entities	Apr. 01, 2009 Consolidation of Retail Joint Ventures [Member] entities	Jul. 01, 2010 Dugan Realty [Member]	Dec. 31, 2010 Dugan Realty [Member]
Significant Acquisitions and Disposals [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage				50.00%
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Loss		$ 1,062,000
Number of Retail Joint Ventures		2	2
Advances to Affiliate	173,000,000
Prior Equity Contributions to Unconsolidated Entities			37,900,000
Payments for Advance to Affiliate			2,000,000
Payments to Acquire Businesses and Interest in Affiliates			2,000,000		166,700,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value		206,852,000	206,852,000	166,306,000
Business Combination, Step Acquisition, Advances to Acquiree Eliminated Upon Consolidation		(173,006,000)	(173,006,000)
Equity Method Investments		34,908,000	34,908,000	158,591,000
Business Acquisition, Put Option Liability Derecognized				(50,000,000)
Equity Method Investments, Net of Liabilities Derecognized				108,591,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net		$ (1,062,000)		$ 57,715,000