Disclosures About Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Summary of financial instruments
Marketable equity securities		$ 24,829
Bank line of credit	261,582
Senior unsecured notes	6,564,842	6,712,624
Mortgage debt	1,653,426	1,676,544
Other debt	78,633	81,958
Carrying Value
Summary of financial instruments
Loans receivable, net	555,791	276,030
Marketable debt securities	225,285	222,809
Marketable equity securities		24,829
Bank line of credit	261,582
Term loan	208,418	222,694
Senior unsecured notes	6,564,842	6,712,624
Mortgage debt	1,653,426	1,676,544
Other debt	78,633	81,958
Carrying Value \| Warrants
Summary of financial instruments
Derivative assets	452	670
Carrying Value \| Interest-rate swap contracts
Summary of financial instruments
Derivative assets	1,487	89
Derivative liabilities	9,610	12,699
Carrying Value \| Currency swap contracts
Summary of financial instruments
Derivative assets	2,218
Derivative liabilities		2,641
Fair Value
Summary of financial instruments
Loans receivable, net	567,280	279,850
Marketable debt securities	255,961	234,137
Marketable equity securities		24,829
Bank line of credit	261,582
Term loan	208,418	222,694
Senior unsecured notes	7,003,556	7,432,012
Mortgage debt	1,696,918	1,771,155
Other debt	78,633	81,958
Fair Value \| Warrants
Summary of financial instruments
Derivative assets	452	670
Fair Value \| Interest-rate swap contracts
Summary of financial instruments
Derivative assets	1,487	89
Derivative liabilities	9,610	12,699
Fair Value \| Currency swap contracts
Summary of financial instruments
Derivative assets	2,218
Derivative liabilities		$ 2,641

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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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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Carrying value as of the balance sheet date of loans from a bank with maturities initially due after one year or beyond the operating cycle if longer, excluding current portion.

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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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