Fees Paid By The Fund And Related Party Transactions - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fees Paid and Related Party Transactions [Line Items]
USCF Management Fee	UNL is contractually obligated to pay USCF a fee, which is paid monthly, that is equal to 0.75% per annum of average daily total net assets.
Percentage of average daily net assets	0.75%
Estimated directors' fees and expenses	$ 555,465	$ 540,586	$ 607,582
Licensing fee incurred	5,001	5,674	7,565
Expense waiver (Note 3)	100,580
Portion Of Non Interest Expense Directors Fees	7,620	5,704	3,808
Licensing Agreements [Member] | First $1,000,000,000 of combined net assets of the funds [Member]
Fees Paid and Related Party Transactions [Line Items]
Fee percentage	0.04%
Licensing Agreements [Member] | First $1,000,000,000 of combined net assets of the funds [Member] | Maximum [Member]
Fees Paid and Related Party Transactions [Line Items]
Combined assets basis for determining fee percentage	1,000,000,000
Licensing Agreements [Member] | Combined net assets above $1,000,000,000 [Member]
Fees Paid and Related Party Transactions [Line Items]
Fee percentage	0.02%
Licensing Agreements [Member] | Combined net assets above $1,000,000,000 [Member] | Minimum [Member]
Fees Paid and Related Party Transactions [Line Items]
Combined assets basis for determining fee percentage	1,000,000,000
Licensing Agreements [Member] | On and after October 20, 2011 [Member]
Fees Paid and Related Party Transactions [Line Items]
Fee percentage	0.015%
Assets basis for determining fee percentage	on all net assets
Future Period - for the year ending December 31, 2013 [Member]
Fees Paid and Related Party Transactions [Line Items]
Estimated investor tax reporting cost	$ 125,000	$ 75,000	$ 55,000
Future Period - for the year ending December 31, 2013 [Member] | Maximum [Member]
Fees Paid and Related Party Transactions [Line Items]
Costs and expenses annual limit for reimbursement	0.15%