Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring	$ 3,733	$ 38,929
Investments in real estate [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring	3,733	10,794
Equity investments [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring		28,135
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) [Member] | Investments in real estate [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) [Member] | Equity investments [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring
Significant Other Observable Inputs (Level 2) [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring
Significant Other Observable Inputs (Level 2) [Member] | Investments in real estate [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring
Significant Other Observable Inputs (Level 2) [Member] | Equity investments [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring
Significant Unobservable Inputs (Level 3) [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring	3,733	38,929
Significant Unobservable Inputs (Level 3) [Member] | Investments in real estate [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring	3,733	10,794
Significant Unobservable Inputs (Level 3) [Member] | Equity investments [Member]
Trusts assets and liabilities measured at fair value on a Non-Recurring Basis
Fair value disclosure, nonrecurring		$ 28,135