XML 70 R38.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2

SIGNIFICANT ACCOUNTING POLICIES - Municipal obligations (Details)	12 Months Ended
	Dec. 31, 2019
Municipal Obligations | Standard & Poor's AA- or higher | Minimum
Marketable Securities:
Maturity term of available-for-sale securities	1 year
Municipal Obligations | Standard & Poor's AA- or higher | Maximum
Marketable Securities:
Maturity term of available-for-sale securities	20 years
Corporate Obligations | Standard & Poor's BBB or higher | Minimum
Marketable Securities:
Maturity term of available-for-sale securities	1 year
Corporate Obligations | Standard & Poor's BBB or higher | Maximum
Marketable Securities:
Maturity term of available-for-sale securities	5 years

X

- Definition

The maturity term of available for sale debt securities held by the entity.

+ References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MunicipalNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsAAMinusRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsBBBRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: