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Organization and Business (Additional Information) (Details) (USD $) | 1 Months Ended |  |  |  |  |  |  |  |
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Dec. 06, 2007 | Dec. 04, 2007 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009 | Feb. 29, 2012 Creation Baskets | Feb. 29, 2012 Redemption Baskets [Member] | Dec. 31, 2013 Beginning on January 1, 2013 and after | Dec. 31, 2013 Open Cleared Swap and Futures Contracts Open Futures Contracts, Long United States Contracts | Dec. 31, 2012 Open Cleared Swap and Futures Contracts Open Futures Contracts, Long United States Contracts
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Contracts |  |  |  |  |  |  |  |  |  |  | 649 | [1] | 1,068 | [2]
Number of shares 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 |  | 11,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Net asset value per share | $ 50.00 |  | $ 42.83 | $ 39.81 | $ 43.46 | $ 42.91 | $ 42.91 |  |  |  |  |  |  |
Number of shares issued | 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Value of shares issued | $ 15,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Commenced investment operations date | Dec. 06, 2007 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of registered shares |  |  | 111,000,000 |  |  |  |  |  |  |  |  |  |  |
[1] | Collateral amounted to $3,548,144 on open futures contracts.
[2] | Collateral amounted to $11,533,650 on open futures contracts.

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