XML 129 R92.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Financial instruments - Natural gas forward contracts (Details) - Natural gas forward contract | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) $ / MMBTU | Dec. 31, 2016 USD ($) $ / MMBTU
Disclosure of financial assets [line items] |  |
Hedge ineffectiveness | $ 0 |
Cash flow hedges |  |
Disclosure of financial assets [line items] |  |
Notional amount | 473,000,000 | $ 484,000,000
Negative fair value | $ 90,200,000 | $ 61,900,000
Cash flow hedges | Geismar 2 Facility |  |
Disclosure of financial assets [line items] |  |
Percentage of gas requirement for forward contracts that will be managed for changes in prices | 40.00% |
Average contract price (in usd per mmbtu) | $ / MMBTU | 3.74 | 3.68
Remaining term | 8 years |
Cash flow hedges | Medicine Hat Facility |  |
Disclosure of financial assets [line items] |  |
Average contract price (in usd per mmbtu) | $ / MMBTU | 1.96 |

X
- Definition The average price of a hedging instrument. [Refer: Hedging instruments [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2018-01-01 -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 23B -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_23B_b&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_AveragePriceOfHedgingInstrument
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
Name: | ifrs-full_DisclosureOfFinancialAssetsLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The fair value of financial liabilities. [Refer: At fair value [member]; Financial liabilities] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 25 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_25&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_FinancialLiabilitiesAtFairValue
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The gain (loss) on hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2018-01-01 -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 24C -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_24C_a_i&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_GainLossOnHedgeIneffectiveness
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The nominal or face amount of a financial instrument, used to calculate payments made on that instrument. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_NotionalAmount
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Hedging Instrument, Term + References No definition available. + Details
Name: | mx_HedgingInstrumentTerm
Namespace Prefix: | mx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage Of Gas Requirement + References No definition available. + Details
Name: | mx_PercentageOfGasRequirement
Namespace Prefix: | mx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | ifrs-full_ClassesOfFinancialLiabilitiesAxis=mx_NaturalGasForwardContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfHedgesAxis=ifrs-full_CashFlowHedgesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mx_RealEstateAndAccumulatedDepreciationDescriptionOfProperty1Axis=mx_Geismar2FacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mx_RealEstateAndAccumulatedDepreciationDescriptionOfProperty1Axis=mx_MedicineHatFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |