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Significant Accounting Policies - Mineral Resources and Mine Development (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($)
Accounting Policies [Abstract] |
Cost of mine development | $ 12.9

X
- Definition Costs incurred related to mine development in the current period. + References No definition available. + Details
Name: | mtrn_CostOfMineDevelopment
Namespace Prefix: | mtrn_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration