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v3.20.4

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Additional Fair Value Elements [Abstract] |  |
Transfers in or out of Level 3 | $ 0.0 | $ 0.0
Fair Value, Measurements, Recurring [Member] |  |
Additional Fair Value Elements [Abstract] |  |
Deferred compensation plan assets | 14.2 | 13.7
Supplementary pension plan assets | 15.0 | 12.8
Cross currency rate swap | 0.4 | 10.2
Interest rate swaps | (7.6) | (5.9)
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] |  |
Additional Fair Value Elements [Abstract] |  |
Deferred compensation plan assets | 0.0 | 0.0
Supplementary pension plan assets | 0.0 | 0.0
Cross currency rate swap | 0.0 | 0.0
Interest rate swaps | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Additional Fair Value Elements [Abstract] |  |
Deferred compensation plan assets | 14.2 | 13.7
Supplementary pension plan assets | 15.0 | 12.8
Cross currency rate swap | 0.4 | 10.2
Interest rate swaps | (7.6) | (5.9)
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] |  |
Additional Fair Value Elements [Abstract] |  |
Deferred compensation plan assets | 0.0 | 0.0
Supplementary pension plan assets | 0.0 | 0.0
Cross currency rate swap | 0.0 | 0.0
Interest rate swaps | $ 0.0 | $ 0.0

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- Definition Fair value portion of asset contracts related to deferred compensation plan. + References No definition available. + Details
Name: | mtx_DeferredCompensationPlanAssetFairValueDisclosure
Namespace Prefix: | mtx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Fair value portion of asset contracts related to interest rate swaps. + References No definition available. + Details
Name: | mtx_InterestRateSwapAssetsFairValueDisclosure
Namespace Prefix: | mtx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Fair value portion of asset contracts related to supplementary pension plan. + References No definition available. + Details
Name: | mtx_SupplementaryPensionPlanAssetFairValueDisclosure
Namespace Prefix: | mtx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
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- Definition Amount of transfers of financial instrument classified as a liability into (out of) level 3 of the fair value hierarchy. + References No definition available. + Details
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- Definition Fair value portion of asset contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward contracts, and swaps. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Period Type: | instant

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- Details
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