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FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) - $ / shares | 6 Months Ended
--- | ---
Jun. 30, 2017 | Jun. 30, 2016
Per Share Operating Performance: |  |  |
Net asset value, beginning of year |  | $ 20.39 | $ 17
Total income (loss) |  | (3.52) | 2.4
Net expenses |  | (0.08) | (0.06)
Net increase (decrease) in net asset value |  | (3.6) | 2.34
Net asset value, end of year |  | $ 16.79 | $ 19.34
Total Return |  | (17.66%) | 13.76%
Ratios to Average Net Assets |  |  |
Total income (loss) |  | (18.40%) | 20.77%
Management fees | [1] | 0.60% | 0.60%
Expenses excluding management fees | [1] | 0.27% | 0.13%
Net income (loss) |  | (18.83%) | 20.40%
[1] | Annualized.

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