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FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) - $ / shares
 3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Per Share Operating Performance:    
Net asset value, beginning of period $ 9.72 $ 13.69
Total income (loss) (0.96) (1.06)
Net expenses (0.02) (0.03)
Net decrease in net asset value (0.98) (1.09)
Net asset value, end of period $ 8.74 $ 12.60
Total Return (10.08%) (7.96%)
Ratios to Average Net Assets    
Total income (loss) (11.06%) (7.42%)
Management fees [1] 0.75% 0.75%
Total expenses excluding management fees [1] 0.93% 0.57%
Expenses waived [1] (0.78%) (0.41%)
Net expenses excluding management fees [1] 0.15% 0.16%
Net income (loss) (11.28%) (7.65%)
[1] Annualized.