Fair Value Measurements (Details 4) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Trust's financial assets for which the fair value option was elected
Financial instruments at fair value	$ 19,705	$ 34,165
Securities carried at fair value [Member] | REIT Preferred Shares [Member]
Trust's financial assets for which the fair value option was elected
Financial instruments at fair value		4,277
Securities carried at fair value [Member] | REIT Common Shares [Member]
Trust's financial assets for which the fair value option was elected
Financial instruments at fair value	19,694	24,579
Loan securities carried at fair value [Member]
Trust's financial assets for which the fair value option was elected
Financial instruments at fair value	$ 11	$ 5,309