Refers to percentage of annual depreciation rate charge for property, plant and equipment.

No definition available.

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Namespace Prefix:	mtx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimate-to-actual adjustment to revenue for shipments sold to customers under PCC contracts. During the year, the price per ton billed to customers is based on periodic estimates of the total annual volume that will be sold to the customer. Revenues are adjusted at the end of each year to reflect the actual volume sold.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The initial length of time that the company's long-term evergreen contracts in effect. Sales of PCC (precipitated calcium carbonate) are predominantly pursuant to long-term evergreen contracts, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The length of time for which a receivable is past due that will trigger an individual review for collectability, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	mtx_PastDueThresholdForIndividualCollectabilityReview
Namespace Prefix:	mtx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

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Name:	us-gaap_AccountsReceivableAdditionalDisclosuresAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of allowance for credit loss on accounts receivable, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82895884-210446

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Name:	us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVenturesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_RevenueRecognitionAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unrealized gain (loss) on investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Balance Type:
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Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_ManufacturingFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=mtx_MachineryAndEquipmentForNaturalStoneMiningAndProcessingPlantsAndChemicalPlantsMember
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Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Cash Equivalents and Short-term Investments [Abstract]
Short-term investments	$ 4.1	$ 1.6	$ 4.1
Unrealized holding gains and losses on short-term bank investments			$ 0.0
Trade Accounts Receivable [Abstract]
Past due threshold for individual collectability review			90 days
Allowance for doubtful accounts	15.0	12.9	$ 15.0
Property, Plant and Equipment [Abstract]
Initial term of long term evergreen contracts			10 years
Investment in Joint Ventures [Abstract]
Equity method investment	17.0	16.1	$ 17.0
Revenue Recognition [Abstract]
Revenue adjustments	$ 0.0	$ 0.0
Buildings [Member] \| Minimum [Member]
Property, Plant and Equipment [Abstract]
Annual rates of depreciation			3.00%
Buildings [Member] \| Maximum [Member]
Property, Plant and Equipment [Abstract]
Annual rates of depreciation			6.67%
Machinery and Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Abstract]
Annual rates of depreciation			6.67%
Machinery and Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Abstract]
Annual rates of depreciation			12.50%
Furniture and Fixtures [Member] \| Minimum [Member]
Property, Plant and Equipment [Abstract]
Annual rates of depreciation			8.00%
Furniture and Fixtures [Member] \| Maximum [Member]
Property, Plant and Equipment [Abstract]
Annual rates of depreciation			12.50%
Computer Equipment and Software-related Assets [Member] \| Minimum [Member]
Property, Plant and Equipment [Abstract]
Annual rates of depreciation			12.50%
Computer Equipment and Software-related Assets [Member] \| Maximum [Member]
Property, Plant and Equipment [Abstract]
Annual rates of depreciation			25.00%
PCC Production Facilities [Member]
Property, Plant and Equipment [Abstract]
Estimated useful life			15 years
Machinery and Equipment for Natural Stone Mining and Processing Plants and Chemical Plants [Member]
Property, Plant and Equipment [Abstract]
Estimated useful life			15 years