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Financial Highlights (Tables) | 6 Months Ended
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Jun. 30, 2015
Financial Highlights [Abstract] |
Per Unit Performance Data and Other Supplemental Financial Data | The following table presents per share performance data and other supplemental financial data for the six months ended June 30, 2015 and 2014 for the shareholders. This information has been derived from information presented in the condensed financial statements.
|  | For the six |  |  | For the six |
|  | months ended |  |  | months ended |
|  | June 30, 2015 |  |  | June 30, 2014 |
|  | (Unaudited) |  |  | (Unaudited) |
Per Share Operating Performance: |  |  |  |  |  |  |  |
Net asset value, beginning of period |  | $ | 26.59 |  |  | $ | 42.83 |
Total income (loss) |  |  | 0.36 |  |  |  | 4.55 |
Total expenses |  |  | (0.11) |  |  |  | (0.21) |
Net increase (decrease) in net asset value |  |  | 0.25 |  |  |  | 4.34 |
Net asset value, end of period |  | $ | 26.84 |  |  | $ | 47.17 |
Total Return |  |  | 0.94 | % |  |  | 10.13 | %
Ratios to Average Net Assets |  |  |  |  |  |  |  |
Total income (loss) |  |  | 5.13 | % |  |  | 9.78 | %
Expenses excluding management fees* |  |  | 0.22 | % |  |  | 0.37 | %
Management fees* |  |  | 0.60 | % |  |  | 0.60 | %
Net income (loss) |  |  | 4.72 | % |  |  | 9.30 | %
* Annualized

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