Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2012

Fair Value Disclosures [Abstract]

Measurement of assets and liabilities at fair value on a recurring basis

The liabilities measured at fair value on a recurring basis were as follows:

	Level 1		Level 2		Level 3		Total
As of December 31, 2012:
Derivative liability for commodity hedges	$	—	$	2,494	$	—	$	2,494
As of December 31, 2011:
Derivative liability for commodity hedges	$	—	$	2,331	$	—	$	2,331
Derivative liability for conversion feature associated with convertible debt	—		—		26,440		26,440

Reconciliation of the change in fair value of Level 3 liabilities

The following reconciliation represents the change in fair value of Level 3 liabilities between January 1, 2012 and December 31, 2012:

	Derivative liability for conversion  feature associated with convertible debt
Fair value as of January 1	$	26,440
Mark-to-market adjustment on conversion feature	15,597
Reclassification from long-term debt to additional paid-in capital	(42,037		)
Fair value as of December 31	$	—

Fair Value Assumptions

The main inputs and assumptions into the fair value model for the Convertible Notes at December 31, 2012 were as follows:

Company's stock price at the end of the period	$	14.77
Expected volatility	22.3		%
Credit spreads	8.22		%
Risk-free interest rate	0.36		%