Derivative Instruments Effects of Derivative Instruments in the Consolidated Statements of Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on derivative instruments	$ (207)	$ 140
Total Impact on Derivative Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on derivative instruments	(1,019)	(52)
Total derivatives designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on derivative instruments	(914)	(126)
Total derivatives designated as hedging instruments | Commodity contracts | Cost of goods sold
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on derivative instruments	(914)	(126)
Total derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on derivative instruments	(105)	74
Total derivatives not designated as hedging instruments | Commodity contracts | Cost of goods sold
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on derivative instruments	147	(21)
Total derivatives not designated as hedging instruments | Commodity contracts | Realized and unrealized (loss) gain on derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on derivative instruments	(207)	140
Total derivatives not designated as hedging instruments | Interest rate swap agreements | Interest expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on derivative instruments	$ (45)	$ (45)