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Organization and Business - Additional Information (Detail) (USD $) | 1 Months Ended |  |  |  |  |  |
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Nov. 30, 2009 PartnershipUnit | Nov. 18, 2009 | Jun. 30, 2012 PartnershipUnit | Dec. 31, 2011 | Jun. 30, 2011 | Dec. 31, 2010 | Feb. 29, 2012 Creation Baskets | Feb. 29, 2012 Prior to February 29, 2012 Creation Baskets | Jun. 30, 2012 Open Cleared Swap and Futures Contracts Open Futures Contracts, Long United States Contract
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Number of contracts |  |  |  |  |  |  |  |  | 1,242
Number of units per basket |  |  |  |  |  |  | 50,000 | 100,000 |
Fee paid by Authorized Purchasers for each order placed to create one or more Creation Baskets or to redeem one or more baskets |  |  | 350 |  | 1,000 |  |  |  |
Number of initially registered units on Form S-1 with the U.S. Securities and Exchange Commission | 30,000,000 |  |  |  |  |  |  |  |
Net asset value per unit |  | $ 50.00 | $ 17.38 | $ 21.21 | $ 32.57 | $ 35.02 |  |  |
Number of units issued |  | 200,000 |  |  |  |  |  |  |
Value of unit issued |  | $ 10,000,000 |  |  |  |  |  |  |
Commenced investment operations date |  | Nov. 18, 2009 |  |  |  |  |  |  |
Number of registered units |  |  | 30,000,000 |  |  |  |  |  |

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