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FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) (USD $)
 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Nov. 18, 2009
Per Unit Operating Performance:      
Net asset value, beginning of period $ 17.23 $ 21.21 $ 50.00
Total income (loss) $ 0.07 $ (3.74)  
Total expenses $ (0.09) $ (0.09)  
Net decrease in net asset value $ (0.02) $ (3.83)  
Net asset value, end of period $ 17.21 $ 17.38 $ 50.00
Total Return (0.12%) (18.06%)  
Ratios to Average Net Assets      
Total income (loss) 5.83% (15.50%)  
Management fees 0.75% [1] 0.75% [1]  
Total expenses excluding management fees 0.38% [1] 0.44% [1]  
Expenses waived (0.17%) [1] (0.20%) [1]  
Net expenses excluding management fees 0.21% [1] 0.24% [1]  
Net income (loss) 5.35% (15.99%)  
[1] Annualized