Fair Value Measurements - Trust's Assets and Liabilities Measured at Fair Value on a Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring	$ 36,369	$ 6,751
Assets Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring	2,356
Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring		6,751
Investments in Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring	22,556
Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring	11,457
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring	36,369	6,751
Significant Unobservable Inputs (Level 3) [Member] | Assets Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring	2,356
Significant Unobservable Inputs (Level 3) [Member] | Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring		6,751
Significant Unobservable Inputs (Level 3) [Member] | Investments in Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring	22,556
Significant Unobservable Inputs (Level 3) [Member] | Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value disclosure, nonrecurring	$ 11,457