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Financial Highlights (Tables) | 3 Months Ended
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Mar. 31, 2013
Financial Highlights [Abstract] |
Per Unit Performance Data and Other Supplemental Financial Data | The following table presents per unit performance data and other supplemental financial data for the three months ended March 31, 2013 and 2012 for the unitholders. This information has been derived from information presented in the condensed financial statements.
|  | For the three months ended March 31, 2013 (Unaudited) |  |  | For the three months ended March 31, 2012 (Unaudited) |
Per Unit Operating Performance: |  |  |  |  |  |  |  |
Net asset value, beginning of period |  | $ | 39.81 |  |  | $ | 43.46 |
Total income (loss) |  |  | 1.32 |  |  |  | 2.43 |
Net expenses |  |  | (0.10 | ) |  |  | (0.08 | )
Net increase in net asset value |  |  | 1.22 |  |  |  | 2.35 |
Net asset value, end of period |  | $ | 41.03 |  |  | $ | 45.81 |
Total Return |  |  | 3.06 | % |  |  | 5.41 | %
Ratios to Average Net Assets |  |  |  |  |  |  |  |
Total income (loss) |  |  | 3.36 | % |  |  | 5.52 | %
Expenses excluding management fees* |  |  | 0.36 | % |  |  | 0.14 | %
Management fees* |  |  | 0.60 | % |  |  | 0.60 | %
Net income (loss) |  |  | 3.12 | % |  |  | 5.34 | %
* Annualized

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