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Fees Paid By The Fund And Related Party Transactions (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Percentage Of Management Fee In Average Daily Total Net Assets	0.75%
Estimated Directors Fees and Expenses	$ 567,863bno_EstimatedDirectorsFeesAndExpenses	$ 555,465bno_EstimatedDirectorsFeesAndExpenses	$ 540,586bno_EstimatedDirectorsFeesAndExpenses
Estimated Investor Tax Reporting Cost	133,000bno_EstimatedInvestorTaxReportingCost	110,000bno_EstimatedInvestorTaxReportingCost	75,000bno_EstimatedInvestorTaxReportingCost
Percentage Of Fees and Other Waivers Expense	0.15%
Expenses Write Off	148,604bno_ExpensesWriteOff
BNO [Member]
Estimated Directors Fees and Expenses	$ 9,150	$ 9,012	$ 9,844