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FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) - $ / shares | 9 Months Ended
--- | ---
Sep. 30, 2015 | Sep. 30, 2014
Per Share Operating Performance: |  |  |
Net asset value, beginning of period |  | $ 13.69 | $ 18.32
Total income (loss) |  | (2.32) | (0.14)
Net expenses |  | (0.09) | (0.14)
Net decrease in net asset value |  | (2.41) | (0.28)
Net asset value, end of period |  | $ 11.28 | $ 18.04
Total Return |  | (17.60%) | (1.53%)
Ratios to Average Net Assets |  |  |
Total income (loss) |  | (14.87%) | 4.47%
Management fees | [1] | 0.75% | 0.75%
Total expenses excluding management fees | [1] | 0.66% | 0.99%
Expenses waived | [1] | (0.51%) | (0.80%)
Net expenses excluding management fees | [1] | 0.15% | 0.19%
Net income (loss) |  | (15.55%) | 3.76%
[1] | Annualized

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