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Financial Highlights (Tables) | 12 Months Ended
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Dec. 31, 2014
Supplemental Financial Information Disclosure [Abstract] |
Schedule Of Per Unit Performance Data and Other Financial Data | The following table presents per share performance data and other supplemental financial data for the years ended December 31, 2014, 2013 and 2012. This information has been derived from information presented in the financial statements.
|  | Year ended |  |  | Year ended |  |  | Year ended |
|  | December 31, 2014 |  |  | December 31, 2013 |  |  | December 31,2012 |
Per Share Operating Performance: |  |  |  |  |  |  |  |  |  |  |  |
Net asset value, beginning of year |  | $ | 43.81 |  |  | $ | 40.98 | * |  | $ | 37.27 | *
Total income (loss) |  |  | (21.06) |  |  |  | 3.24 |  |  |  | 4.10 | *
Net expenses |  |  | (0.36) |  |  |  | (0.41) |  |  |  | (0.39) | *
Net increase (decrease) in Net Asset Value |  |  | (21.42) |  |  |  | 2.83 |  |  |  | 3.71 | *
Net asset value, end of year |  | $ | 22.39 |  |  | $ | 43.81 |  |  | $ | 40.98 | *
Total Return |  |  | (48.89) | % |  |  | 6.91 | % |  |  | 9.95 | %
Ratios to Average Net Assets |  |  |  |  |  |  |  |  |  |  |  |
Total income (loss) |  |  | (68.25) | % |  |  | 6.66 | % |  |  | 9.44 | %
Management fees |  |  | 0.75 | % |  |  | 0.75 | % |  |  | 0.75 | %
Total expenses excluding management fees |  |  | 0.56 | % |  |  | 0.45 | % |  |  | 0.32 | %
Expenses waived |  |  | (0.39) | % |  |  | (0.20) | % |  |  | (0.09) | %
Net expenses excluding management fees |  |  | 0.17 | % |  |  | 0.25 | % |  |  | 0.23 | %
Net income (loss) |  |  | (69.17) | % |  |  | 5.66 | % |  |  | 8.46 | %
| * | On August 26, 2013, BNO executed a 2-for-1 forward share split for all shareholders of record as of the close of markets on August 26, 2013. The 2-for-1 forward share split was payable after the close of markets on August 28, 2013. BNO began trading at its post split price on August 29, 2013. The Financial Highlights have been adjusted for the periods shown to reflect the 2-for-1 forward share split on a retroactive basis.

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