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Financial Highlights (Per Unit Performance Data and Other Supplemental Financial Data) (Detail) (USD $) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Apr. 10, 2006
Per Share Operating Performance: |  |  |  |  |
Net asset value, beginning of year | $ 20.15 uso_NetAssetValuePerUnit |  | $ 35.23 uso_NetAssetValuePerUnit |  | $ 67.39 uso_NetAssetValuePerUnit
Total income (loss) | $ (3.25)uso_TotalIncomeLossPerUnit |  | $ 1.45 uso_TotalIncomeLossPerUnit |  |
Total expenses | $ (0.03)uso_TotalExpensesPerUnit |  | $ (0.07)uso_TotalExpensesPerUnit |  |
Net increase (decrease) in net asset value | $ (3.28)uso_IncreaseDecreaseInNetAssetValuePerUnit |  | $ 1.38 uso_IncreaseDecreaseInNetAssetValuePerUnit |  |
Net asset value, end of year | $ 16.87 uso_NetAssetValuePerUnit |  | $ 36.61 uso_NetAssetValuePerUnit |  | $ 67.39 uso_NetAssetValuePerUnit
Total Return | (16.28%)uso_RateOfReturnOnAverageAsset |  | 3.92%uso_RateOfReturnOnAverageAsset |  |
Ratios to Average Net Assets |  |  |  |  |
Total income (loss) | (11.82%)uso_PercentageOfTotalRevenue |  | 4.57%uso_PercentageOfTotalRevenue |  |
Expenses excluding management fees | 0.27%uso_ExpensesExcludingManagementFeePercentage | [1] | 0.34%uso_ExpensesExcludingManagementFeePercentage | [1] |
Management fees | 0.45%uso_ManagementIncentiveFeePercentage | [1] | 0.45%uso_ManagementIncentiveFeePercentage | [1] |
Net income (loss) | (12.00%)uso_PercentageOfConsolidatedNetIncomeLoss |  | 4.37%uso_PercentageOfConsolidatedNetIncomeLoss |  |
[1] | Annualized

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