Basis Of Presentation And Summary Of Significant Accounting Policies (Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value) (Details) (USD $)	Sep. 30, 2011		Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage and notes payable	$ 3,179,034,000		$ 3,047,586,000
Unsecured senior notes	3,016,986,000		3,016,598,000
Unsecured exchangeable senior notes	1,754,343,000		1,721,817,000
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage and notes payable	3,179,034,000		3,047,586,000
Unsecured senior notes	3,016,986,000		3,016,598,000
Unsecured exchangeable senior notes	1,754,343,000	[1]	1,721,817,000	[1]
Total	7,950,363,000		7,786,001,000
Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage and notes payable	3,337,861,000		3,121,193,000
Unsecured senior notes	3,073,469,000		3,241,542,000
Unsecured exchangeable senior notes	1,909,227,000		1,929,291,000
Total	8,320,557,000		8,292,026,000
ASC 470-20 Adjustment [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net of the adjustment for the equity component allocation	$ 64,700,000		$ 93,600,000

[1] Includes the net impact of Accounting Standards Codification ("ASC") ASC 470-20 (formerly known as FSP No. APB 14-1) totaling approximately $64.7 million and $93.6 million at September 30, 2011 and December 31, 2010, respectively.