Fair Value Measurement (Policy)	3 Months Ended
Mar. 31, 2012
Fair Value Disclosures [Abstract]
Fair Value Measurement Policy [Policy Text Block]	Financial Assets and Liabilities Measured at Fair Value Financial assets and liabilities that are measured at fair value in our consolidated financial statements consist of (i) marketable securities, (ii) derivative positions in marketable equity securities, (iii) the assets in our deferred compensation plan (for which there is a corresponding liability on our consolidated balance sheet), (iv) Real Estate Fund investments, and (v) mandatorily redeemable instruments (Series G-1 through G-4 convertible preferred units and Series D-13 cumulative redeemable preferred units). In determining fair value, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible, as well as consider counterparty credit risk in our assessment of fair value. Considerable judgment is necessary to interpret Level 2 and 3 inputs in determining the fair value of our financial and non-financial assets and liabilities. Accordingly, our fair value estimates, which are made at the end of each reporting period, may be different than the amounts that may ultimately be realized upon sale or disposition of these assets. Financial Assets and Liabilities not Measured at Fair Value Financial assets and liabilities that are not measured at fair value in our consolidated financial statements include mezzanine loans receivable and our secured and unsecured debt. Estimates of the fair values of these instruments are determined by the standard practice of modeling the contractual cash flows required under the instrument and discounting them back to their present value at the appropriate current risk adjusted interest rate, which is provided by a third-party specialist. For floating rate debt, we use forward rates derived from observable market yield curves to project the expected cash flows we would be required to make under the instrument. The fair value of our mezzanine loans receivable is classified as Level 3 and the fair value of our secured and unsecured debt is classified as Level 2.

Fair Value Measurement (Policy)

3 Months Ended

Mar. 31, 2012

Fair Value Measurement Policy [Policy Text Block]

Financial Assets and Liabilities Measured at Fair Value

Financial assets and liabilities that are measured at fair value in our consolidated financial statements consist of (i) marketable securities, (ii) derivative positions in marketable equity securities, (iii) the assets in our deferred compensation plan (for which there is a corresponding liability on our consolidated balance sheet), (iv) Real Estate Fund investments, and (v) mandatorily redeemable instruments (Series G-1 through G-4 convertible preferred units and Series D-13 cumulative redeemable preferred units).

In determining fair value, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible, as well as consider counterparty credit risk in our assessment of fair value. Considerable judgment is necessary to interpret Level 2 and 3 inputs in determining the fair value of our financial and non-financial assets and liabilities. Accordingly, our fair value estimates, which are made at the end of each reporting period, may be different than the amounts that may ultimately be realized upon sale or disposition of these assets.

Financial Assets and Liabilities not Measured at Fair Value

Financial assets and liabilities that are not measured at fair value in our consolidated financial statements include mezzanine loans receivable and our secured and unsecured debt. Estimates of the fair values of these instruments are determined by the standard practice of modeling the contractual cash flows required under the instrument and discounting them back to their present value at the appropriate current risk adjusted interest rate, which is provided by a third-party specialist. For floating rate debt, we use forward rates derived from observable market yield curves to project the expected cash flows we would be required to make under the instrument. The fair value of our mezzanine loans receivable is classified as Level 3 and the fair value of our secured and unsecured debt is classified as Level 2.