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Financial Instruments, Off-Balance Sheet Risks And Contingencies (Details Textual) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Schedule of Cost-method Investments [Line Items]    
Money Market Funds, at Carrying Value $ 8,010,771us-gaap_MoneyMarketFundsAtCarryingValue  
Cash Deposits and Investments In Treasuries $ 45,561,253bno_CashDepositsAndInvestmentsInTreasuries $ 20,517,551bno_CashDepositsAndInvestmentsInTreasuries