Fair Value Measurements - Financial Assets and Liabilities Accounted at Fair Value (Detail) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contracts, Assets	$ 3,577,996	$ 8,230,156
Commodity contracts, Liabilities	1,345,504	716,488
Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity contracts, Assets	3,577,996	8,230,156
Commodity contracts, Liabilities	1,345,504	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	3,577,996	8,230,156
Commodity contracts, Liabilities	$ 1,345,504	$ 716,488