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Significant Accounting Policies (Narrative) (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Significant Accounting Policies [Abstract]      
Basket of shares 50,000    
Fair value transfers $ 0 $ 0  
Reserve for uncertain tax positions $ 0 $ 0  
Annualized rate of Sponsors Fee before waiver 0.45% 0.45% 0.45%
Annualized rate of Sponsors Fee [1] 0.30% 0.30% 0.30%
Sponsor's Fees $ 1,039,540 $ 957,096 $ 854,317
Sponsor fees waived 519,770 478,548 427,159
Fees payable to Sponsor 89,564 78,954  
All other expenses $ 0 $ 0 $ 0
[1] The Expense ratio is calculated net of the Sponsor's voluntary fee waiver (refer to Note 2.7). Exclusive of the Sponsor's voluntary fee waiver, the gross expense ratio is 0.45% for the years ending December 31, 2017, 2016, and 2015.