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	Jun. 30, 2012		Dec. 31, 2011
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable	$ 2,877,125		$ 3,123,267
Unsecured senior notes	4,863,413		3,865,186
Unsecured exchangeable senior notes	1,155,669		1,715,685
Net of the adjustment for the equity component allocation	39,463
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable	2,877,125		3,123,267
Unsecured senior notes	4,863,413		3,865,186
Unsecured exchangeable senior notes	1,155,669	[1]	1,715,685	[1]
Total	8,896,207		8,704,138
Estimate of Fair Value, Fair Value Disclosure [Member]
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable	2,985,393		3,297,903
Unsecured senior notes	5,236,475		4,148,461
Unsecured exchangeable senior notes	1,328,569		1,904,115
Total	9,550,437		9,350,479
ASC 470-20 Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Net of the adjustment for the equity component allocation	$ 39,500		$ 54,500

[1] Includes the net impact of Accounting Standards Codification ("ASC") ASC 470-20 totaling approximately $39.5 million and $54.5 million at June 30, 2012 and December 31, 2011, respectively.