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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 period |  | $ 11.75 | $ 9.72
Total income (loss) |  | (1.68) | 0.96
Net expenses |  | (0.05) | (0.04)
Net decrease in net asset value |  | (1.73) | 0.92
Net asset value, end of period |  | $ 10.02 | $ 10.64
Total Return |  | (14.72%) | 9.47%
Ratios to Average Net Assets |  |  |
Total income (loss) |  | (20.02%) | 10.53%
Management fees | [1] | 0.75% | 0.75%
Total expenses excluding management fees | [1] | 0.57% | 0.91%
Expenses waived | [1] | (0.42%) | (0.76%)
Net expenses excluding management fees | [1] | 0.15% | 0.15%
Net income (loss) |  | (20.47%) | 10.09%
[1] | Annualized.

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