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FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) - $ / shares | 6 Months Ended
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Jun. 30, 2017 | Jun. 30, 2016
Per Share Operating Performance: |  |  |  |
Net asset value, beginning of period |  | $ 9.29 | $ 8.69 |
Total income (loss) |  | (2.46) | 0 | [1]
Total expenses |  | (0.05) | (0.04) |
Net increase (decrease) in net asset value |  | (2.51) | (0.04) |
Net asset value, end of period |  | $ 6.78 | $ 8.65 |
Total Return |  | (27.02%) | (0.46%) |
Ratios to Average Net Assets |  |  |  |
Total income (loss) |  | (29.11%) | 7.65% |
Management fees | [2] | 0.60% | 0.60% |
Expenses excluding management fees | [2] | 0.73% | 0.58% |
Net income (loss) |  | (29.77%) | 7.06% |
[1] | Amount less than $0.005.
[2] | Annualized.

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