XML 74 R60.htm IDEA: XBRL DOCUMENT
v3.8.0.1

EMPLOYEE BENEFIT PLANS - Weighted average asset allocation by asset category along with target allocation (Details) - Retirement Income Plan | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets | 100.00% | 100.00%
Target Allocation for 2018 | 100.00% |
Cash and Cash Equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets | 2.90% | 3.30%
Domestic Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets | 42.30% | 25.50%
International Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets | 20.70% | 20.80%
Fixed Income Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets | 23.80% | 25.30%
Investments measured at net asset value |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets | 10.30% | 25.10%
Minimum | Cash and Cash Equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 0.00% |
Minimum | Domestic Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 0.00% |
Minimum | International Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 0.00% |
Minimum | Fixed Income Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 15.00% |
Minimum | Investments measured at net asset value |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 0.00% |
Maximum | Cash and Cash Equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 3.00% |
Maximum | Domestic Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 40.00% |
Maximum | International Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 20.00% |
Maximum | Fixed Income Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 25.00% |
Maximum | Investments measured at net asset value |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Allocation for 2018 | 12.00% |

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_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=mpx_DomesticEquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=mpx_InternationalEquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=mpx_InvestmentsMeasuredAtNetAssetValueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |