Disclosures About Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Bank line of credit	$ 454,000
Senior unsecured notes	5,416,063	3,318,379
Mortgage debt	1,764,571	1,235,779
Other debt	87,985	92,187
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Loans receivable, net	110,253	2,002,866
Marketable equity securities	17,053
Bank line of credit	454,000
Senior unsecured notes	5,416,063	3,318,379
Mortgage debt	1,764,571	1,235,779
Other debt	87,985	92,187
Carrying Value \| Interest-rate swap contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets		3,865
Derivative liabilities	12,123	7,920
Carrying Value \| Warrants
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets	1,334	1,500
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Loans receivable, net	111,073	2,026,389
Marketable equity securities	17,053
Bank line of credit	454,000
Senior unsecured notes	5,819,304	3,536,413
Mortgage debt	1,870,070	1,258,185
Other debt	87,985	92,187
Fair Value \| Interest-rate swap contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets		3,865
Derivative liabilities	12,123	7,920
Fair Value \| Warrants
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets	$ 1,334	$ 1,500

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 represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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- Definition

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