Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Using Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis
Available-for-sale real estate equity securities	$ 301,945	$ 274,274
Real estate related bonds	0	0
Total assets	301,945	274,274
Derivative interest rate instruments	0	0
Total liabilities	0	0
Using Significant Other Observable Inputs (Level 2) [Member]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis
Available-for-sale real estate equity securities	0	0
Real estate related bonds	21,516	15,091
Total assets	21,516	15,091
Derivative interest rate instruments	(1,735)	(2,284)
Total liabilities	(1,735)	(2,284)
Using Significant Other Unobservable Inputs (Level 3) [Member]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis
Available-for-sale real estate equity securities	0	0
Real estate related bonds	0	0
Total assets	0	0
Derivative interest rate instruments	0	0
Total liabilities	$ 0	$ 0

- Definition

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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