Basis Of Presentation And Summary Of Significant Accounting Policies (Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable	$ 2,848,686		$ 3,123,267
Unsecured senior notes	4,639,217		3,865,186
Unsecured exchangeable senior notes	1,162,955		1,715,685
Net of the adjustment for the equity component allocation	32,533
ASC 470-20 Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Net of the adjustment for the equity component allocation	32,500		54,500
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable	2,848,686		3,123,267
Unsecured senior notes	4,639,217		3,865,186
Unsecured exchangeable senior notes	1,162,955	[1]	1,715,685	[1]
Total	8,650,858		8,704,138
Estimate of Fair Value, Fair Value Disclosure [Member]
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable	2,968,017		3,297,903
Unsecured senior notes	5,163,293		4,148,461
Unsecured exchangeable senior notes	1,325,431		1,904,115
Total	$ 9,456,741		$ 9,350,479

[1] Includes the net impact of Accounting Standards Codification ("ASC") ASC 470-20 totaling approximately $32.5 million and $54.5 million at September 30, 2012 and December 31, 2011, respectively.