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Derivative Financial Instruments - Cash deposits (Detail) - Zero Cost Collar And Forward Contracts [Member] - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Deposit Assets [Line Items] |  |
Deposit with counterparty | $ 0 | $ 1,000
SC [Member] |  |
Deposit Assets [Line Items] |  |
Deposit with counterparty | $ 0 | $ 1,000

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- Definition Deposit assets [LineItems]. + References No definition available. + Details
Name: | mx_DepositAssetsLineItems
Namespace Prefix: | mx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(17)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-6 + Details
Name: | us-gaap_MarginDepositAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=mx_ZeroCostCollarAndForwardContractsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_CounterpartyNameAxis=mx_StandardCharteredBankKoreaLimitedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |