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ORGANIZATION AND BUSINESS (Additional Information) (Details) | Dec. 06, 2007 USD ($) $ / shares shares | Mar. 31, 2018 Contracts $ / shares $ / Units | Dec. 31, 2017 $ / shares | Mar. 31, 2017 $ / shares | Dec. 31, 2016 $ / shares | Dec. 04, 2007 Contracts
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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 |  |  |  |
Net asset value per share | $ / shares | $ 50.00 | $ 22.65 | $ 21.05 | $ 18.52 | $ 20.39 |
Number of shares issued | shares | 300,000 |  |  |  |  |
Value of shares issued | $ | $ 15,000,000 |  |  |  |  |
Number of registered shares | Contracts |  | 111,000,000 |  |  |  | 11,000,000
Creation Baskets |  |  |  |  |  |
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items] |  |  |  |  |  |
Number of shares per basket |  | 50,000 |  |  |  |

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