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Fair Value of Financial Instruments (Valuation of Securities Using Fair Value Hierarchy) (Detail) (USD $)
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Dec. 31, 2013
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Dec. 31, 2012
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Short-Term Investments
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| Schedule of Trading Securities and Other Trading Assets [Line Items] | ||
| Securities, fair value | $ 48,493,330 | $ 51,194,826 |
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Exchange-Traded Futures Contracts | United States
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| Schedule of Trading Securities and Other Trading Assets [Line Items] | ||
| Securities, fair value | 2,598,553 | 2,608,343 |
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Fair Value, Inputs, Level 1 | Short-Term Investments
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| Schedule of Trading Securities and Other Trading Assets [Line Items] | ||
| Securities, fair value | 48,493,330 | 51,194,826 |
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Fair Value, Inputs, Level 1 | Exchange-Traded Futures Contracts | United States
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| Schedule of Trading Securities and Other Trading Assets [Line Items] | ||
| Securities, fair value | $ 2,598,553 | $ 2,608,343 |