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EMPLOYEE BENEFIT PLANS - Amounts recorded in consolidated balance sheet as pension liabilities (Details) - USD ($) $ in Thousands | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | ---
EMPLOYEE BENEFIT PLANS |  |
SERP liability | $ (14,440) | $ (15,564)

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- Definition This element represents the amount of defined benefit plan contributions and deferrals of supplemental retirement plan. + References No definition available. + Details
Name: | mpx_DefinedBenefitPlanSupplementalExecutiveRetirementPlanContributionsAndDeferrals
Namespace Prefix: | mpx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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