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Derivative Financial Instruments - Fair Value of Outstanding Forward and Zero Cost Collar Recorded as Assets (Detail) (Zero cost collars [Member], USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Asset Derivatives:  
Derivatives designated as hedging instruments, Asset $ 4,912us-gaap_DerivativeAssets
Derivative designated as hedging instruments [Member] | Other current assets [Member]  
Asset Derivatives:  
Derivatives designated as hedging instruments, Asset $ 4,912us-gaap_DerivativeAssets
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherCurrentAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= mx_ZeroCostCollarsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember