Derivative Instruments (Details) (Maximum)	3 Months Ended
	Mar. 31, 2015
Derivative Instruments
Percentage of the forecasted intercompany sales to be hedged by using foreign currency risk derivatives	75.00%
Percentage of the forecasted natural gas requirements to be hedged by using derivatives	75.00%
Foreign currency forward exchange contracts
Derivative Instruments
Maturity period of derivatives	18 months
Foreign exchange option contracts
Derivative Instruments
Maturity period of derivatives	18 months
Natural gas contracts | Forward contracts
Derivative Instruments
Maturity period of derivatives	24 months