Equity Investments - Summarized Balance Sheets of Real Estate Investments (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
ASSETS
Cash and cash equivalents	$ 165,762,000	$ 97,682,000	$ 159,251,000	$ 40,952,000
Securities carried at fair value	7,074,000	19,694,000
Restricted cash held in escrows	19,084,000	13,250,000
Other assets	28,135,000	2,464,000
TOTAL ASSETS	968,485,000	923,163,000
LIABILITIES AND MEMBERS' CAPITAL
TOTAL LIABILITIES AND EQUITY	968,485,000	923,163,000
Carrying value of the Trust's investment in Vintage Housing Holding	139,061,000	134,859,000
Vintage Housing Holding LLC [Member]
ASSETS
Cash and cash equivalents	5,469,000	6,555,000
Real estate, net	360,851,000	340,666,000
Restricted cash held in escrows	45,380,000	41,878,000
Receivables and other assets	19,964,000	26,681,000
TOTAL ASSETS	431,664,000	415,780,000
LIABILITIES AND MEMBERS' CAPITAL
Mortgage and notes payable	313,078,000	298,654,000
Other liabilities	47,443,000	53,687,000
Non-controlling interests	18,006,000	15,997,000
Members' Capital	53,137,000	47,442,000
TOTAL LIABILITIES AND EQUITY	431,664,000	415,780,000
Carrying value of the Trust's investment in Vintage Housing Holding	33,706,000	30,534,000
CDH CDO LLC [Member]
ASSETS
Cash and cash equivalents	2,031,000	1,885,000
Real estate debt investments carried at fair value	183,110,000	185,060,000
Securities carried at fair value	80,463,000	95,994,000
Real estate, net		19,909,000
Interest and other receivables	1,066,000	1,030,000
Other assets	319,000	3,893,000
TOTAL ASSETS	266,989,000	307,771,000
LIABILITIES AND MEMBERS' CAPITAL
Collateralized debt obligation carried at fair value	153,361,000	191,345,000
Mortgage and notes payable		22,293,000
Interest rate swap liability	8,270,000	11,413,000
Other liabilities	2,727,000	5,423,000
Non-controlling interests	102,000	102,000
Members' Capital	102,529,000	77,195,000
TOTAL LIABILITIES AND EQUITY	266,989,000	307,771,000
Carrying value of the Trust's investments in CDH CDO LLC	4,181,000	322,000
Carrying value of the Trust's investment in Vintage Housing Holding