FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS - (Additional Information) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fees Paid and Related Party Transactions [Line Items]
USCF Management Fee									UNL is contractually obligated to pay USCF a fee, which is paid monthly, equal to 0.75% per annum of average daily total net assets
Estimated directors fees and expenses									$ 1,929	$ 2,888	$ 3,140
Assets basis for determining fee percentage									on all net assets
Licensing fee incurred									$ 1,576	2,046	2,377
Expense waiver (Note 3)	$ (17,165)	$ (19,588)	$ (9,907)	$ (15,053)	$ (25,375)	$ (28,986)	$ (24,115)	$ (23,616)	$ 61,713	102,092	89,122
Licensing Agreements [Member]
Fees Paid and Related Party Transactions [Line Items]
Fee percentage									0.015%
Future Period - for the year ending December 31, 2016 [Member]
Fees Paid and Related Party Transactions [Line Items]
Estimated investor tax reporting cost									$ 72,000	76,000	86,000
Future Period - for the year ending December 31, 2016 [Member] | Maximum [Member]
Fees Paid and Related Party Transactions [Line Items]
Costs and expenses annual limit for reimbursement									0.15%
UNL [Member] | Related Public Funds [Member]
Fees Paid and Related Party Transactions [Line Items]
Estimated directors fees and expenses									$ 536,375	$ 582,050	$ 569,303