Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior unsecured notes	$ 1,358,182	$ 1,358,008
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	525,834	543,000
Mortgage and mezzanine loans receivable	175,699	225,359
Total assets	701,533	768,359
Mortgages payable	8,582,573	8,663,326
Senior unsecured notes	1,358,182	1,358,008
Revolving credit facility debt	83,982	1,170,000
Total debt	10,024,737	11,191,334
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	525,834	543,000
Mortgage and mezzanine loans receivable	175,331	221,446
Total assets	701,165	764,446
Mortgages payable	8,571,000	8,690,000
Senior unsecured notes	1,427,000	1,468,000
Revolving credit facility debt	83,982	1,170,000
Total debt	$ 10,081,982	$ 11,328,000

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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