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Financial Highlights (Tables) | 6 Months Ended
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Jun. 30, 2012
Per Unit Performance Data and Other Supplemental Financial Data | The following table presents per unit performance data and other supplemental financial data for the six months ended June 30, 2012 and 2011 for the unitholders. This information has been derived from information presented in the condensed financial statements.
|  | For the six months ended June 30, 2012 (Unaudited) |  |  | For the six months ended June 30, 2011 (Unaudited) |
Per Unit Operating Performance: |  |  |  |  |  |  |  |
Net asset value, beginning of period |  | $ | 43.46 |  |  | $ | 42.91 |
Total income (loss) |  |  | (5.40 | ) |  |  | 1.07 |
Net expenses |  |  | (0.16 | ) |  |  | (0.19 | )
Net increase (decrease) in net asset value |  |  | (5.56 | ) |  |  | 0.88 |
Net asset value, end of period |  | $ | 37.90 |  |  | $ | 43.79 |
Total Return |  |  | (12.79 | )% |  |  | 2.05 | %
Ratios to Average Net Assets |  |  |  |  |  |  |  |
Total income (loss) |  |  | (10.50 | )% |  |  | 2.93 | %
Expenses excluding management fees* |  |  | 0.15 | % |  |  | 0.23 | %
Management fees* |  |  | 0.60 | % |  |  | 0.60 | %
Net income (loss) |  |  | (10.87 | )% |  |  | 2.52 | %
* | Annualized

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- Definition Per Unit Performance Data and Other Supplemental Financial Data [Table Text Block] + References No definition available. + Details
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