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Variable to Fixed Price Commodity Swaps Derivative Instruments (Detail) (Fair Value, Measurements, Recurring, USD $)
Dec. 31, 2012
Fair Value, Inputs, Level 2
 
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Crude oil contracts $ 1,800,295
Fair Value, Inputs, Level 3
 
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Marketable Securities $ 1,018,573