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: |