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FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) - $ / shares | 9 Months Ended
--- | ---
Sep. 30, 2016 | Sep. 30, 2015
Per Share Operating Performance: |  |  |
Net asset value, beginning of period |  | $ 17 | $ 26.59
Total income (loss) |  | 1.84 | (5.99)
Total expenses |  | (0.09) | (0.15)
Net increase (decrease) in net asset value |  | 1.75 | (6.14)
Net asset value, end of period |  | $ 18.75 | $ 20.45
Total Return |  | 10.29% | (23.09%)
Ratios to Average Net Assets |  |  |
Total income (loss) |  | 17.46% | (20.93%)
Management fees | [1] | 0.60% | 0.60%
Expenses excluding management fees | [1] | 0.12% | 0.20%
Net income (loss) |  | 16.91% | (21.53%)
[1] | Annualized.

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