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Fair Value Measurements - Financial Assets and Liabilities Accounted at Fair Value (Detail) (USD $)
Jun. 30, 2014
Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity contracts, Assets      
Commodity contracts, Liabilities 2,701,354 125,773
Commodity Contract [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity contracts, Assets      
Commodity contracts, Liabilities 2,701,354 125,773
Fair Value Measurements Recurring [Member] | Fair Value Measurements, Level 1 [Member] | Commodity Contract [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity contracts, Assets      
Fair Value Measurements Recurring [Member] | Fair Value Measurements, Level 2 [Member] | Commodity Contract [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity contracts, Assets      
Commodity contracts, Liabilities 2,701,354 125,773
Fair Value Measurements Recurring [Member] | Fair Value Measurements, Level 3 [Member] | Commodity Contract [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Commodity contracts, Assets