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Summary of Significant Accounting Policies - Additional Information (Detail) |  |  | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2012 | Feb. 29, 2012 Creation Baskets | Feb. 29, 2012 Redemption Baskets | Feb. 29, 2012 Prior to February 29, 2012 Creation Baskets | Feb. 29, 2012 Prior to February 29, 2012 Redemption Baskets | Dec. 31, 2012 Maximum
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Minimum likelihood of tax benefits being recognized upon ultimate settlement | 50.00% |  |  |  |  |
Number of units per basket |  | 50,000 | 50,000 | 100,000 | 100,000 |
Cash equivalents maturity period |  |  |  |  |  | 6 months

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- Definition Cash Equivalents, Maturity Period + References No definition available. + Details
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- Definition Number of Units per Basket + References No definition available. + Details
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- Definition Percentage Of Income Tax Examination Minimum Likelihood of Tax Benefits Being Realized Upon Settlement + References No definition available. + Details
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- Details
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