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FEES PAID BY THE FUND AND RELATED PARTY TRANSACTIONS - Additional Information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Percentage Of Management Fee In Average Daily Total Net Assets 0.75%    
Estimated Investor Tax Reporting Cost $ 90,200 $ 111,000 $ 190,000
Percentage Of Fees and Other Waivers Expense 0.15%    
Expenses Write Off $ 80,032    
BNO [Member]      
Estimated Directors Fees and Expenses 19,301 15,970 13,325
BNO and Related Public Fund [Member]      
Estimated Directors Fees and Expenses $ 556,951 $ 521,689 $ 536,375