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Fair Value Measurements - Schedule of Fair Value of Long-term Borrowings (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Long-term Borrowings:    
Carrying amount of senior notes $ 224,035us-gaap_LongTermDebtNoncurrent $ 223,923us-gaap_LongTermDebtNoncurrent
6.625% senior notes due 2021 [Member] | Senior notes [Member] | Significant Other Observable Inputs (Level 2) [Member]    
Long-term Borrowings:    
Carrying amount of senior notes 224,035us-gaap_LongTermDebtNoncurrent
/ us-gaap_DebtInstrumentAxis
= mx_SixPointSixTwoFiveZeroPercentageSeniorSecuredNotesDueTwoThousandTwentyOneMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember		 223,923us-gaap_LongTermDebtNoncurrent
/ us-gaap_DebtInstrumentAxis
= mx_SixPointSixTwoFiveZeroPercentageSeniorSecuredNotesDueTwoThousandTwentyOneMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
Estimated fair value of senior notes $ 206,100us-gaap_NotesPayableFairValueDisclosure
/ us-gaap_DebtInstrumentAxis
= mx_SixPointSixTwoFiveZeroPercentageSeniorSecuredNotesDueTwoThousandTwentyOneMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember		 $ 229,500us-gaap_NotesPayableFairValueDisclosure
/ us-gaap_DebtInstrumentAxis
= mx_SixPointSixTwoFiveZeroPercentageSeniorSecuredNotesDueTwoThousandTwentyOneMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember