Fair Value Measurements - Financial Assets and Liabilities Accounted at Fair Value (Detail) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contracts, Assets	$ 4,536,666	$ 8,230,156
Commodity contracts, Liabilities	1,491,045	716,488
Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contracts, Assets	4,536,666	8,230,156
Commodity contracts, Liabilities	1,491,045	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, Assets	4,536,666	8,230,156
Commodity contracts, Liabilities	$ 1,491,045	$ 716,488