XML 96 R77.htm IDEA: XBRL DOCUMENT
v3.20.4

Benefit Plans - Pension Assets by Percentage (Details) - Pension Plan [Member] | 12 Months Ended
--- | ---
Dec. 26, 2020 | Dec. 28, 2019
Asset category [Abstract] |  |
Total plan assets (as a percent) | 100.00% | 100.00%
Expected long-term rate of return on plan assets | 4.69% | 3.84%
Fixed Income Funds [Member] |  |
Asset category [Abstract] |  |
Total plan assets (as a percent) | 0.00% | 55.00%
Equity Securities [Member] |  |
Asset category [Abstract] |  |
Total plan assets (as a percent) | 66.00% | 25.00%
Multi-Asset [Member] |  |
Asset category [Abstract] |  |
Total plan assets (as a percent) | 24.00% | 9.00%
Cash and Cash Equivalents [Member] |  |
Asset category [Abstract] |  |
Total plan assets (as a percent) | 1.00% | 7.00%
Alternative Investments [Member] |  |
Asset category [Abstract] |  |
Total plan assets (as a percent) | 9.00% | 4.00%
Maximum [Member] | Equity Securities [Member] |  |
Asset category [Abstract] |  |
Total plan assets (as a percent) | 70.00% |
Maximum [Member] | Alternative Investments [Member] |  |
Asset category [Abstract] |  |
Total plan assets (as a percent) | 10.00% |

X
- Definition Refers to the expected long term return on plan assets. + References No definition available. + Details
Name: | mli_DefinedBenefitPlanExpectedReturnOnPlanAssetsPercentage
Namespace Prefix: | mli_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Percentage of actual 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/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=118255775&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_FixedIncomeSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=mli_AlternativeInvestmentsMember
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: |