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FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS (Additional Information) (Details) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
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                 $ 1,447 $ 1,929 $ 2,888
Licensing fee incurred                 964 1,576 2,046
Expense waiver $ (14,866) $ (11,999) $ (15,329) $ (17,762) $ (17,165) $ (19,588) $ (9,907) $ (15,053) $ 59,956 61,713 102,092
Licensing Agreements [Member]                      
Fees Paid and Related Party Transactions [Line Items]                      
Fee percentage                 0.015%    
Future Period - for the year ending December 31, 2018 [Member]                      
Fees Paid and Related Party Transactions [Line Items]                      
Estimated investor tax reporting cost                 $ 65,000 72,000 76,000
Future Period - for the year ending December 31, 2018 [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                 $ 1,447 $ 1,929 $ 2,888