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FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value of Derivative Instruments) (Detail) - USD ($)
Dec. 31, 2017
Dec. 31, 2016
Commodity Contracts [Member] | Assets [Member] | Future [Member]    
Derivatives Fair Value [Line Items]    
Derivatives not Accounted for as Hedging Instruments $ 117,780,350 $ 111,290,560