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Financial Highlights (Per Unit Performance Data and Other Supplemental Financial Data) (Details) (USD $) | 6 Months Ended |
--- | --- | ---
Jun. 30, 2014 | Jun. 30, 2013 | Dec. 06, 2007
Per Unit Operating Performance: |  |  |  |  |
Net Asset Value Per Share, Beginning | $ 42.83 |  | $ 39.81 |  | $ 50.00
Total income | $ 4.55 |  | $ 0.46 |  |
Total expenses | $ (0.21) |  | $ (0.20) |  |
Net increase in net asset value | $ 4.34 |  | $ 0.26 |  |
Net Asset Value Per Share, Ending | $ 47.17 |  | $ 40.07 |  | $ 50.00
Total Return | 10.13% |  | 0.65% |  |
Ratios to Average Net Assets |  |  |  |  |
Total income | 9.78% |  | 1.27% |  |
Management fees | 0.60% | [1] | 0.60% | [1] |
Expenses excluding management fees | 0.37% | [1] | 0.39% | [1] |
Net income | 9.30% |  | 0.78% |  |
[1] | Annualized

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