Schedule of Derivative Instruments, Gain (Loss) in Statements of Financial Performance (Details) (Not Designated as Hedging Instrument, USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (2,329)	$ (2,091)	$ (4,604)	$ 4,559
Cost of Sales | Forward Contracts | Commodity Contracts
Derivative Instruments, Gain (Loss)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (2,329)	$ (2,091)	$ (4,604)	$ 4,559