Equity Investments - Summarized Statements of Operations of Real Estate Equity Investments (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Interest, dividends and discount accretion	$ 3,917,000	$ 3,722,000	$ 13,545,000	$ 15,018,000
Expenses
Interest expense	5,435,000	4,416,000	18,175,000	11,560,000
Real estate taxes	1,705,000	1,160,000	4,184,000	3,116,000
General and administrative	1,113,000	782,000	3,058,000	2,447,000
Vintage Housing Holding LLC [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total revenue	11,048,000	10,328,000	32,451,000	30,928,000
Expenses
Operating	4,649,000	4,254,000	13,952,000	12,250,000
Real estate taxes	128,000	139,000	397,000	442,000
Interest	485,000	1,503,000	1,480,000	4,824,000
Depreciation and amortization	446,000	978,000	1,137,000	6,605,000
Other expenses	1,453,000	1,323,000	4,176,000	4,048,000
Total expenses	7,161,000	8,197,000	21,142,000	28,169,000
Net income (loss)	3,887,000	2,131,000	11,309,000	2,759,000
Loss attributable to non-controlling interests	676,000	29,000	1,399,000	791,000
Net income	4,563,000	2,160,000	12,708,000	3,550,000
Trust's share of net income	2,525,000	1,392,000	7,142,000	2,326,000
CDH CDO LLC [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Interest, dividends and discount accretion	4,469,000	4,688,000	12,654,000	13,362,000
Expenses
Interest expense	1,598,000	1,651,000	4,791,000	5,012,000
Fees and expenses paid to related party	250,000	250,000	750,000	750,000
General and administrative	328,000	304,000	891,000	964,000
Total expenses	2,176,000	2,205,000	6,432,000	6,726,000
Net investment income:	2,293,000	2,483,000	6,222,000	6,636,000
Net property income	(55,000)	(5,000)	(205,000)	(282,000)
Loss on sale of real estate	(2,909,000)		(2,909,000)
Gain on extinguishment of debt	4,827,000		4,827,000
Realized gain (loss) from investments	13,367,000	1,716,000	13,361,000	(1,042,000)
Unrealized gain (loss) from investments	391,000	620,000	5,886,000	7,436,000
Net income	17,914,000	4,814,000	27,182,000	12,748,000
Trust's share of net income	$ 3,367,000	$ 855,000	$ 4,274,000	$ 1,333,000