XML 53 R27.htm IDEA: XBRL DOCUMENT v2.4.0.6
Financial Highlights (Per Unit Performance Data and Other Supplemental Financial Data) (Details) (USD $)
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 06, 2007
Per Unit Operating Performance:      
Net asset value, beginning of period $ 39.81 $ 43.46 $ 50.00
Total income (loss) $ 1.32 $ 2.43  
Net expenses $ (0.10) $ (0.08)  
Net increase in net asset value $ 1.22 $ 2.35  
Net asset value, end of period $ 41.03 $ 45.81 $ 50.00
Total Return 3.06% 5.41%  
Ratios to Average Net Assets      
Total income (loss) 3.36% 5.52%  
Expenses excluding management fees 0.36% [1] 0.14% [1]  
Management fees 0.60% [1] 0.60% [1]  
Net income (loss) 3.12% 5.34%  
[1] * Annualized