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Organization and Business (Additional Information) (Details) | Dec. 06, 2007 USD ($) $ / shares shares | Dec. 04, 2007 | Jun. 30, 2015 Contracts $ / shares $ / Units | Dec. 31, 2014 $ / shares | Jun. 30, 2014 $ / shares | Dec. 31, 2013 $ / shares
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Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items] |  |  |  |  |  |  |
Fee paid by Authorized Purchasers for each order placed to create one or more Creation Baskets or to redeem one or more baskets |  |  |  | 350 |  |  |
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 | $ / shares |  | $ 50.00 |  | $ 26.84 | $ 26.59 | $ 47.17 | $ 42.83
Number of shares issued | shares |  | 300,000 |  |  |  |  |
Value of shares issued | $ |  | $ 15,000,000 |  |  |  |  |
Number of registered shares |  |  |  | 111,000,000 |  |  |
Creation Baskets |  |  |  |  |  |  |
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items] |  |  |  |  |  |  |
Number of shares per basket |  |  |  | 50,000 |  |  |
Open Futures Contracts, Long | United States |  |  |  |  |  |  |
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items] |  |  |  |  |  |  |
Number of Contracts | [1] |  |  | 1,321 |  |  |
[1] | Collateral amounted to $8,457,363 on open future contracts.

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