Derivative Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative Instruments
Asset Derivatives	$ 2,411	$ 2,155
Liability Derivatives	1,028	861
Derivatives designated as hedging instruments | Foreign exchange contracts | Other current assets
Derivative Instruments
Asset Derivatives	2,061	1,665
Derivatives designated as hedging instruments | Foreign exchange contracts | Other assets
Derivative Instruments
Asset Derivatives	111	182
Derivatives designated as hedging instruments | Foreign exchange contracts | Accrued pension and other liabilities
Derivative Instruments
Liability Derivatives	1
Derivatives designated as hedging instruments | Natural gas contracts | Accounts payable and accrued liabilities
Derivative Instruments
Liability Derivatives	672	427
Derivatives designated as hedging instruments | Natural gas contracts | Accrued pension and other liabilities
Derivative Instruments
Liability Derivatives	143	372
Derivatives not designated as hedging instruments | Foreign exchange contracts | Other current assets
Derivative Instruments
Asset Derivatives	239	308
Derivatives not designated as hedging instruments | Foreign exchange contracts | Accounts payable and accrued liabilities
Derivative Instruments
Liability Derivatives	$ 212	$ 62