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FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS (Details) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS                      
Estimated directors fees and expenses                 $ 1,096 $ 1,447 $ 1,929
Licensing fee incurred                 651 964 1,576
Expense waiver $ 16,101 $ 16,088 $ 21,137 $ 20,977 $ 14,866 $ 11,999 $ 15,329 $ 17,762 $ 74,303 59,956 61,713
Licensing Agreements [Member]                      
FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS                      
Fee percentage                 0.015%    
Future Period - for the year ending December 31, 2019 [Member]                      
FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS                      
Estimated investor tax reporting cost                 $ 77,834 65,000 72,000
Future Period - for the year ending December 31, 2019 [Member] | Maximum [Member]                      
FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS                      
Costs and expenses annual limit for reimbursement                 0.15%    
UNL [Member]                      
FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS                      
Percentage of Contractual Obligated to Pay                 0.75%    
Estimated directors fees and expenses                 $ 1,096 1,447 1,929
UNL [Member] | Related Public Funds [Member]                      
FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS                      
Estimated directors fees and expenses                 $ 556,951 $ 521,689 $ 536,375