Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

No definition available.

Name:	mtx_DerivativesNotionalAmount
Namespace Prefix:	mtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Fair value of all derivative assets designated as fair value hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

+ Details

Name:	us-gaap_FairValueHedgeAssetsAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of all derivative liabilities designated as fair value hedging instruments.

+ References

+ Details

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

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherNoncurrentLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=mtx_OtherAssetsAndDeferredChargesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CrossCurrencyInterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivative Financial Instruments (Details) - USD ($) $ in Millions	Sep. 29, 2019	Sep. 30, 2018	Jul. 03, 2016
Interest Rate Swaps [Member] \| Other Non-current Liabilities [Member]
Derivative, Fair Value [Abstract]
Notional amount	$ 150.0
Fair value of derivative liability	7.3
Interest Rate Swaps [Member] \| Designated as Hedging Instrument [Member]
Derivative, Fair Value [Abstract]
Notional amount	100.0		$ 300.0
Interest Rate Swaps [Member] \| Designated as Hedging Instrument [Member] \| Other Assets and Deferred Charges [Member]
Derivative, Fair Value [Abstract]
Fair value of derivative assets	0.5
Cross Currency Rate Swap [Member] \| Other Assets and Deferred Charges [Member]
Derivative, Fair Value [Abstract]
Notional amount	150.0	$ 150.0
Fair value of derivative assets	$ 14.1