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Per Unit Performance Data and Other Supplemental Financial Data (Detail) (USD $) | 6 Months Ended |
--- | --- | ---
Jun. 30, 2012 | Jun. 30, 2011 | Dec. 06, 2007
Per Unit Operating Performance: |  |  |  |  |
Net Asset Value Per Unit, Beginning | $ 43.46 |  | $ 42.91 |  | $ 50.00
Total income (loss) | $ (5.40) |  | $ 1.07 |  |
Net expenses | $ (0.16) |  | $ (0.19) |  |
Net increase (decrease) in net asset value | $ (5.56) |  | $ 0.88 |  |
Net Asset Value Per Unit, Ending | $ 37.90 |  | $ 43.79 |  | $ 50.00
Total Return | (12.79%) |  | 2.05% |  |
Ratios to Average Net Assets |  |  |  |  |
Total income (loss) | (10.50%) |  | 2.93% |  |
Expenses excluding management fees | 0.15% | [1] | 0.23% | [1] |
Management fees | 0.60% | [1] | 0.60% | [1] |
Net income (loss) | (10.87%) |  | 2.52% |  |
[1] | Annualized

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