4. Derivatives (Tables)

6 Months Ended

Jun. 30, 2016

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of Derivatives Not Designated as Hedging Instruments

	As of June 30, 2016
	Assets			Liabilities
Type of Instrument	Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value
Commodity contracts	Derivative instruments	$	13,299	Derivative instruments	$	12,166
		$	13,299		$	12,166

	As of December 31, 2015
	Assets			Liabilities
Type of Instrument	Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value
Commodity contracts	Derivative instruments	$	2,081	Derivative instruments	$	1,848
		$	2,081		$	1,848

Schedule of Recognized Gains (Losses) for Derivatives

		Realized Gains (Losses)
		Three Months Ended June 30,
Type of Instrument	Statements of Operations Location	2016			2015
Commodity contracts	Cost of goods sold	$	(999	)	$	264
		$	(999	)	$	264
		Unrealized Gains (Losses)
			Three Months Ended June 30,
Type of Instrument	Statements of Operations Location	2016			2015
Commodity contracts	Cost of goods sold	$	1,227		$	(552	)
		$	1,227		$	(552	)
		Realized Gains (Losses)
			Six Months Ended June 30,
Type of Instrument	Statements of Operations Location	2016			2015
Commodity contracts	Cost of goods sold	$	(91	)	$	149
		$	(91	)	$	149
		Unrealized Gains (Losses)
			Six Months Ended June 30,
Type of Instrument	Statements of Operations Location	2016			2015
Commodity contracts	Cost of goods sold	$	900		$	(626	)
		$	900		$	(626	)