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Condensed Statement of Changes in Partners' Capital (USD $)
Total
General Partner [Member]
Limited Partner [Member]
Balances at Dec. 31, 2014 $ 41,419,390us-gaap_PartnersCapital $ 0us-gaap_PartnersCapital
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember		 $ 41,419,390us-gaap_PartnersCapital
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_LimitedPartnerMember
Net asset value, beginning of period at Dec. 31, 2014 $ 22.39bno_NetAssetValuePerUnit    
Addition of 3,550,000 partnership shares 71,769,789us-gaap_PartnersCapitalAccountContributions 0us-gaap_PartnersCapitalAccountContributions
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember		 71,769,789us-gaap_PartnersCapitalAccountContributions
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_LimitedPartnerMember
Redemption of 100,000 partnership shares (2,041,445)us-gaap_PartnersCapitalAccountRedemptions 0us-gaap_PartnersCapitalAccountRedemptions
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember		 (2,041,445)us-gaap_PartnersCapitalAccountRedemptions
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_LimitedPartnerMember
Net income (loss) (2,629,411)us-gaap_ProfitLoss 0us-gaap_ProfitLoss
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember		 (2,629,411)us-gaap_ProfitLoss
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_LimitedPartnerMember
Balances at Mar. 31, 2015 $ 108,518,323us-gaap_PartnersCapital $ 0us-gaap_PartnersCapital
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember		 $ 108,518,323us-gaap_PartnersCapital
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_LimitedPartnerMember
Net asset value, end of period at Mar. 31, 2015 $ 20.48bno_NetAssetValuePerUnit