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ORGANIZATION AND BUSINESS (Additional Information) (Details)
Dec. 06, 2007
USD ($)
$ / shares
shares
Jun. 30, 2018
$ / shares
$ / Units
Dec. 31, 2017
$ / shares
Jun. 30, 2017
$ / shares
Dec. 31, 2016
$ / shares
Dec. 04, 2007
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 $ 25.37 $ 21.05 $ 16.79 $ 20.39  
Number of shares issued | shares 300,000          
Value of shares issued | $ $ 15,000,000          
Number of registered shares   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