Disclosures About Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Marketable debt securities	$ 214,860
Marketable equity securities	17,396	17,053
Bank line of credit	215,015	454,000
Senior unsecured notes	5,615,979	5,416,063
Mortgage debt	1,726,944	1,764,571
Other debt	84,060	87,985
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Loans receivable, net	125,521	110,253
Marketable debt securities	214,860
Marketable equity securities	17,396	17,053
Bank line of credit	215,015	454,000
Senior unsecured notes	5,615,979	5,416,063
Mortgage debt	1,726,944	1,764,571
Other debt	84,060	87,985
Carrying Value \| Warrants
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets	1,385	1,334
Carrying Value \| Interest-rate swap contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative liabilities	12,903	12,123
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Loans receivable, net	125,233	111,073
Marketable debt securities	214,860
Marketable equity securities	17,396	17,053
Bank line of credit	215,015	454,000
Senior unsecured notes	6,198,028	5,819,304
Mortgage debt	1,829,647	1,870,070
Other debt	84,060	87,985
Fair Value \| Warrants
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets	1,385	1,334
Fair Value \| Interest-rate swap contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative liabilities	$ 12,903	$ 12,123

For an unclassified balance sheet, this item represents equity securities categorized neither as held-to-maturity nor trading.

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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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For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

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This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

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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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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 loan receivable as presented on the statement of financial position which may include mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts, or any other loans which are due the Company as of the balance sheet date.

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The carrying amount as of the balance sheet date for the aggregate of other miscellaneous borrowings owed by the reporting entity.

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Carrying value as of the balance sheet date , including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

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