Related-Party Transactions - Fees and Reimbursements Paid by the Trust (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Related Party Transaction [Line Items]
Management fee paid	$ 2,847	$ 2,738	$ 5,620	$ 5,417
FUR Advisors [Member]
Related Party Transaction [Line Items]
Management fee paid	$ 23	$ 29	$ 48	$ 58