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Lease obligations - Extension options (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Disclosure of Finance Leases [Line Items] |  |
Lease liabilities recognized (discounted) | $ 722,234 |
Potential future lease payments not included in lease liabilities (undiscounted) | 53,364 | $ 70,600
Ocean going vessels |  |
Disclosure of Finance Leases [Line Items] |  |
Lease liabilities recognized (discounted) | 472,322 |
Potential future lease payments not included in lease liabilities (undiscounted) | 5,994 |
Terminals and tanks |  |
Disclosure of Finance Leases [Line Items] |  |
Lease liabilities recognized (discounted) | 194,938 |
Potential future lease payments not included in lease liabilities (undiscounted) | 30,161 |
Other |  |
Disclosure of Finance Leases [Line Items] |  |
Lease liabilities recognized (discounted) | 54,974 |
Potential future lease payments not included in lease liabilities (undiscounted) | $ 17,209 |

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- Definition [Line Items] for Disclosure of Finance Leases [Table] + References No definition available. + Details
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Data Type: | xbrli:stringItemType
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- Definition Finance Lease, Liability, Payment, Due1 + References No definition available. + Details
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Namespace Prefix: | mx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Lessee, Finance Lease, Option to Extend, Amount + References No definition available. + Details
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Namespace Prefix: | mx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |