Fair Value Measurements - Financial Assets and Liabilities Accounted at Fair Value (Detail) - USD ($)	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contracts	$ 13,846,635	$ 8,230,156
Commodity contracts	987,964	716,488
Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contracts	13,846,635	8,230,156
Commodity contracts	987,964	716,488
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	13,846,635	8,230,156
Commodity contracts	$ 987,964	$ 716,488