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NET SALES - Payment Terms (Details)	9 Months Ended
	Sep. 30, 2020
Minimum
Net sales:
Revenue satisfaction period	7 days
Maximum
Net sales:
Revenue satisfaction period	10 days

X

- Definition

The satisfaction period of revenue remaining performance obligation.

+ References

No definition available.

+ Details

Name:	mpx_RevenueRemainingPerformanceObligationSatisfactionPeriod
Namespace Prefix:	mpx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: