Fair Value Measurements (Details) (Forward Contracts, Not Designated as Hedging Instrument, Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability for commodity hedges	$ 1,537	$ 2,871
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability for commodity hedges	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability for commodity hedges	1,537	2,871
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability for commodity hedges	$ 0	$ 0