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Fair Value Of Financial Instruments (Fair Value of Derivative Instruments) (Detail) (Futures [Member], Commodity Contracts [Member], Assets [Member], USD $) | Mar. 31, 2015 | Dec. 31, 2014
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Futures [Member] | Commodity Contracts [Member] | Assets [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivatives not Accounted for as Hedging Instruments | $ (115,984,140)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsTotalMember / us-gaap_DerivativeByNatureAxis = us-gaap_FutureMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | $ (167,617,930)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsTotalMember / us-gaap_DerivativeByNatureAxis = us-gaap_FutureMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember

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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 Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624163-113959 + Details
Name: | us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | us-gaap_DerivativesFairValueLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration