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Effect of Derivative Instruments on Condensed Statements of Operations (Detail) (USD $) | 3 Months Ended | 6 Months Ended
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Jun. 30, 2012 | Jun. 30, 2011 | Jun. 30, 2012 | Jun. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Realized Gain or (Loss) on Derivatives Recognized in Income | $ (6,014,750) | $ 13,159,190 | $ (3,856,050) | $ 21,292,660
Change in Unrealized Gain or (Loss) on Derivatives Recognized in Income |  |  | (12,464,380) | (14,501,200)
Commodity Contracts | Futures | Realized gain on closed positions |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Realized Gain or (Loss) on Derivatives Recognized in Income |  |  | (3,856,050) | 21,292,660
Commodity Contracts | Futures | Change in unrealized gain on open positions |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Change in Unrealized Gain or (Loss) on Derivatives Recognized in Income |  |  | $ (12,464,380) | $ (14,501,200)

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- Definition The net realized gain (loss) on investments sold during the period, not including gains (losses) on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, which, for cash flow reporting, is a component of proceeds from investing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open derivatives, commodity, or energy contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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