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Fair Value of Financial Instrument (Effect of Derivative Instruments on Condensed Statements of Operations) (Detail) (USD $)
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12 Months Ended | ||
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Dec. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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| Derivative Instruments, Gain (Loss) [Line Items] | |||
| Realized Gain or (Loss) on Derivatives Recognized in Income | $ 3,496,995 | $ 17,063,315 | $ 13,406,173 |
| Change in Unrealized Gain or (Loss) on Derivatives Recognized in Income | (9,790) | (2,121,382) | 1,464,309 |
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Commodity Contracts | Futures | Realized gain (loss) on closed positions
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| Derivative Instruments, Gain (Loss) [Line Items] | |||
| Realized Gain or (Loss) on Derivatives Recognized in Income | 3,496,995 | 17,063,315 | 13,406,173 |
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Commodity Contracts | Futures | Change in unrealized gain (loss) on open positions
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| Derivative Instruments, Gain (Loss) [Line Items] | |||
| Change in Unrealized Gain or (Loss) on Derivatives Recognized in Income | $ (9,790) | $ (2,121,382) | $ 1,464,309 |