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Fair Value of Derivative Instruments (Detail) (Commodity Contracts, Futures, Assets, USD $) | Dec. 31, 2012 | Dec. 31, 2011
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Commodity Contracts | Futures | Assets |  |
Derivatives, Fair Value [Line Items] |  |
Derivatives not Accounted for as Hedging Instruments | $ 1,556,910 | $ 4,002,120

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- Definition Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959 + Details
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