Related-Party Transactions - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2014
Related Party Transaction [Line Items]
Management fees	$ 5,632,000
FUR Advisors [Member]
Related Party Transaction [Line Items]
Percentage of equity contributions	1.50%
Percentage of equity contributions by unaffiliated third parties	0.25%
Percentage of amount available for distribution in excess of threshold amount	20.00%
Threshold amount		$ 569,963,000
Percentage of growth rate on incentive fee		4.00%
Yield plus percentage	4.26%	2.50%
Threshold amount required to be distributed before incentive fee	$ 432,214,000
Per share Threshold amount required to be distributed	$ 12.06
Incentive fees	$ 13,879,000
Percentage of positive difference between appraised net asset value and threshold amount on termination	20.00%
Reduced threshold amount	$ 104,980,000
Percentage of dividends paid on disposition	20.00%
Additional liquidating distributions per common share	$ 9.13
Base asset management fee	$ 9,496,000
Additional liquidating distributions paid per common share	$ 10.18
Supplemental fee payment terms, description	payable if there is (i) a termination of the Advisory Agreement for any reason other than for cause (as defined) by the Trust or with cause by the Trust’s Advisor, (ii) a disposition of all or substantially all of the Trust’s assets, or (iii) an election by the Trust to orderly liquidate the Trust’s assets. The termination fee, if payable, is equal to the lesser of (i) the base management fee paid to the Trust’s Advisor for the prior twelve month period or (ii) either (x) in the case of a termination of the Advisory Agreement, 20% of the positive difference, if any between (A) the appraised net asset value of the Trust’s assets at the date of termination and (B) the threshold amount less $104,980,000, or (y) in the case of a disposition or liquidation, 20% of any dividends paid on account of the Trust’s Common Shares at such time as the threshold amount is reduced to $104,980,000, which will be achieved at such time as aggregate distributions of approximately $9.13 per Common Share in excess of the Growth Factor have been paid.
Termination fees	$ 9,496,000
Payable to related parties included in related party fees payable	1,420,000
FUR Advisors [Member] | US Treasury Bill Securities [Member]
Related Party Transaction [Line Items]
Period for growth factor on incentive		5 years
Winthrop Management LP [Member]
Related Party Transaction [Line Items]
Payable to related parties included in related party fees payable	152,000
Related Party [Member]
Related Party Transaction [Line Items]
Management fees	$ 1,420,000