Derivative Instruments (Details)	12 Months Ended
	Dec. 31, 2013
Foreign currency forward exchange contracts | Maximum
Derivative Instruments
Maturity period of derivatives	18 months
Foreign exchange option contracts | Maximum
Derivative Instruments
Maturity period of derivatives	18 months
Natural gas forward contracts | Minimum
Derivative Instruments
Maturity period of derivatives	1 month
Natural gas forward contracts | Maximum
Derivative Instruments
Maturity period of derivatives	18 months