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FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) - $ / shares | 9 Months Ended
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Sep. 30, 2016 | Sep. 30, 2015
Per Share Operating Performance: |  |  |
Net asset value, beginning of period |  | $ 9.72 | $ 9.72
Total income (loss) |  | 0.48 | (2.32)
Net expenses |  | (0.06) | (0.09)
Net decrease in net asset value |  | 0.42 | (2.41)
Net asset value, end of period |  | $ 10.14 | $ 11.28
Total Return |  | 4.32% | (17.60%)
Ratios to Average Net Assets |  |  |
Total income (loss) |  | 4.93% | (14.87%)
Management fees | [1] | 0.75% | 0.75%
Total expenses excluding management fees | [1] | 0.93% | 0.66%
Expenses waived | [1] | (0.78%) | (0.51%)
Net expenses excluding management fees | [1] | 0.15% | 0.15%
Net income (loss) |  | 4.26% | (15.55%)
[1] | Annualized.

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