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FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) (USD $)
 3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Nov. 18, 2009
Per Unit Operating Performance:      
Net asset value, beginning of period $ 18.32 $ 17.23 $ 50.00
Total income $ 1.36 $ 2.09  
Net expenses $ (0.05) $ (0.04)  
Net increase in net asset value $ 1.31 $ 2.05  
Net asset value, end of period $ 19.63 $ 19.28 $ 50.00
Total Return 7.15% 11.90%  
Ratios to Average Net Assets      
Total income 8.92% 11.51%  
Management fees 0.75% [1] 0.75% [1]  
Total expenses excluding management fees 0.87% [1] 0.34% [1]  
Expenses waived (0.64%) [1] (0.13%) [1]  
Net expenses excluding management fees 0.23% [1] 0.21% [1]  
Net income 8.68% 11.27%  
[1] Annualized