Related-Party Transactions - Fees and Reimbursements Paid by the Trust (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Related Party Transaction [Line Items]
Management fee paid	$ 2,715	$ 2,725	$ 8,335	$ 8,142
FUR Advisors [Member]
Related Party Transaction [Line Items]
Management fee paid	$ 7	$ 21	$ 14	$ 78