Summary Of Significant Accounting Policies (Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable	$ 3,102,485		$ 3,123,267
Unsecured senior notes	4,639,528		3,865,186
Unsecured exchangeable senior notes	1,170,356		1,715,685
Total	3,063,841
Impact of accounting pronouncement	25,491		54,500
Carrying Amount [Member]
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable	3,102,485		3,123,267
Unsecured senior notes	4,639,528		3,865,186
Unsecured exchangeable senior notes	1,170,356	[1]	1,715,685	[1]
Total	8,912,369		8,704,138
Estimated Fair Value [Member]
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable	3,256,940		3,297,903
Unsecured senior notes	5,162,486		4,148,461
Unsecured exchangeable senior notes	1,278,554		1,904,115
Total	9,697,980		9,350,479
ASC 470-20 Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Impact of accounting pronouncement	$ 25,500		$ 54,500

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