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Industry Segments (Details) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 27, 2014 | Sep. 28, 2013 | Dec. 27, 2014 | Dec. 28, 2013 | Dec. 29, 2012
Segment Reporting Information [Line Items] |  |  |  |  |
Percentage of net consolidated sales threshold constituting a major customer (in hundredths) |  |  | 10.00%mli_SegmentReportingPercentageOfNetConsolidatedSalesThresholdConstitutingMajorCustomer | 10.00%mli_SegmentReportingPercentageOfNetConsolidatedSalesThresholdConstitutingMajorCustomer | 10.00%mli_SegmentReportingPercentageOfNetConsolidatedSalesThresholdConstitutingMajorCustomer
Proforma net sales |  |  | $ 2,364,227,000 us-gaap_SalesRevenueGoodsNet | $ 2,158,541,000 us-gaap_SalesRevenueGoodsNet | $ 2,189,938,000 us-gaap_SalesRevenueGoodsNet
Long-lived assets | 386,883,000 us-gaap_NoncurrentAssets |  | 386,883,000 us-gaap_NoncurrentAssets | 373,050,000 us-gaap_NoncurrentAssets | 356,961,000 us-gaap_NoncurrentAssets
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 2,364,227,000 us-gaap_SalesRevenueGoodsNet | 2,158,541,000 us-gaap_SalesRevenueGoodsNet | 2,189,938,000 us-gaap_SalesRevenueGoodsNet
Cost of goods sold |  |  | 2,043,719,000 us-gaap_CostOfGoodsSold | 1,862,089,000 us-gaap_CostOfGoodsSold | 1,904,463,000 us-gaap_CostOfGoodsSold
Depreciation and amortization |  |  | 33,735,000 us-gaap_OtherDepreciationAndAmortization | 32,394,000 us-gaap_OtherDepreciationAndAmortization | 31,495,000 us-gaap_OtherDepreciationAndAmortization
Selling, general, and administrative expense |  |  | 131,740,000 us-gaap_SellingGeneralAndAdministrativeExpense | 134,914,000 us-gaap_SellingGeneralAndAdministrativeExpense | 129,456,000 us-gaap_SellingGeneralAndAdministrativeExpense
Litigation settlement |  |  |  |  | (4,050,000)us-gaap_LitigationSettlementAmount
Insurance settlement |  |  | 0 us-gaap_GainOnBusinessInterruptionInsuranceRecovery | (106,332,000)us-gaap_GainOnBusinessInterruptionInsuranceRecovery | (1,500,000)us-gaap_GainOnBusinessInterruptionInsuranceRecovery
(Gain) loss on disposal of assets | (4,800,000)us-gaap_GainLossOnDispositionOfAssets | (39,800,000)us-gaap_GainLossOnDispositionOfAssets | (6,259,000)us-gaap_GainLossOnDispositionOfAssets | (39,765,000)us-gaap_GainLossOnDispositionOfAssets | 0 us-gaap_GainLossOnDispositionOfAssets
Impairment charges |  |  | 0 us-gaap_AssetImpairmentCharges | 4,304,000 us-gaap_AssetImpairmentCharges | 0 us-gaap_AssetImpairmentCharges
Severance | 4,200,000 us-gaap_SeveranceCosts1 |  | 7,296,000 us-gaap_SeveranceCosts1 | 0 us-gaap_SeveranceCosts1 | 3,369,000 us-gaap_SeveranceCosts1
Operating income |  |  | 153,996,000 us-gaap_OperatingIncomeLoss | 270,937,000 us-gaap_OperatingIncomeLoss | 126,705,000 us-gaap_OperatingIncomeLoss
Interest expense |  |  | (5,740,000)us-gaap_InterestExpense | (3,990,000)us-gaap_InterestExpense | (6,890,000)us-gaap_InterestExpense
Other (expense) income, net |  |  | (243,000)us-gaap_OtherNonoperatingIncomeExpense | 4,451,000 us-gaap_OtherNonoperatingIncomeExpense | 539,000 us-gaap_OtherNonoperatingIncomeExpense
Income before income taxes |  |  | 148,013,000 us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 271,398,000 us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 120,354,000 us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments
Expenditures for long-lived assets |  |  | 66,286,000 us-gaap_PropertyPlantAndEquipmentAdditions | 65,320,000 us-gaap_PropertyPlantAndEquipmentAdditions | 65,457,000 us-gaap_PropertyPlantAndEquipmentAdditions
Segment assets | 1,328,096,000 us-gaap_Assets |  | 1,328,096,000 us-gaap_Assets | 1,247,767,000 us-gaap_Assets | 1,104,155,000 us-gaap_Assets
Corporate and Eliminations [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | (12,388,000)us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | (14,549,000)us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | (22,898,000)us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | (12,388,000)us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | (14,549,000)us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | (22,898,000)us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
Cost of goods sold |  |  | (12,386,000)us-gaap_CostOfGoodsSold / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | (14,488,000)us-gaap_CostOfGoodsSold / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | (22,696,000)us-gaap_CostOfGoodsSold / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
Depreciation and amortization |  |  | 2,203,000 us-gaap_OtherDepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | 2,252,000 us-gaap_OtherDepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | 1,547,000 us-gaap_OtherDepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
Selling, general, and administrative expense |  |  | 22,743,000 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | 24,964,000 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | 26,328,000 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
Litigation settlement |  |  |  |  | (4,050,000)us-gaap_LitigationSettlementAmount / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
Insurance settlement |  |  |  | (2,437,000)us-gaap_GainOnBusinessInterruptionInsuranceRecovery / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | 0 us-gaap_GainOnBusinessInterruptionInsuranceRecovery / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
(Gain) loss on disposal of assets |  |  | 0 us-gaap_GainLossOnDispositionOfAssets / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | 0 us-gaap_GainLossOnDispositionOfAssets / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |
Impairment charges |  |  |  | 0 us-gaap_AssetImpairmentCharges / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |
Severance |  |  | 0 us-gaap_SeveranceCosts1 / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember |  | 3,369,000 us-gaap_SeveranceCosts1 / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
Operating income |  |  | (24,948,000)us-gaap_OperatingIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | (24,840,000)us-gaap_OperatingIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | (27,396,000)us-gaap_OperatingIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
United States [Member] | Reportable Geographical Components [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 1,752,548,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US | 1,676,385,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US | 1,696,589,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US
Long-lived assets | 322,178,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US |  | 322,178,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US | 325,667,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US | 306,023,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 1,752,548,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US | 1,676,385,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US | 1,696,589,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_US
United Kingdom [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Net assets of foreign operations | 112,600,000 mli_NetAssets / us-gaap_StatementGeographicalAxis = country_GB |  | 112,600,000 mli_NetAssets / us-gaap_StatementGeographicalAxis = country_GB |  |
United Kingdom [Member] | Reportable Geographical Components [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 326,832,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB | 229,659,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB | 234,684,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB
Long-lived assets | 43,064,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB |  | 43,064,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB | 22,159,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB | 23,496,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 326,832,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB | 229,659,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB | 234,684,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = country_GB
Other [Member] | Reportable Geographical Components [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 284,847,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember | 252,497,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember | 258,665,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember
Long-lived assets | 21,641,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember |  | 21,641,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember | 25,224,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember | 27,442,000 us-gaap_NoncurrentAssets / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 284,847,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember | 252,497,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember | 258,665,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_ReportableGeographicalComponentsMember / us-gaap_StatementGeographicalAxis = mli_CountryOtherMember
Mexico [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Net assets of foreign operations | 50,400,000 mli_NetAssets / us-gaap_StatementGeographicalAxis = country_MX |  | 50,400,000 mli_NetAssets / us-gaap_StatementGeographicalAxis = country_MX |  |
Luxembourg [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Net assets of foreign operations | 45,700,000 mli_NetAssets / us-gaap_StatementGeographicalAxis = country_LU |  | 45,700,000 mli_NetAssets / us-gaap_StatementGeographicalAxis = country_LU |  |
China [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Net assets of foreign operations | 23,900,000 mli_NetAssets / us-gaap_StatementGeographicalAxis = country_CN |  | 23,900,000 mli_NetAssets / us-gaap_StatementGeographicalAxis = country_CN |  |
Tube and Fittings [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 1,143,164,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_TubeAndFittingsMember | 972,107,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_TubeAndFittingsMember | 986,825,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_TubeAndFittingsMember
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 1,143,164,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_TubeAndFittingsMember | 972,107,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_TubeAndFittingsMember | 986,825,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_TubeAndFittingsMember
Brass Rod and Forgings [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 556,985,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_BrassRodAndForgingsMember | 553,896,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_BrassRodAndForgingsMember | 583,940,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_BrassRodAndForgingsMember
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 556,985,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_BrassRodAndForgingsMember | 553,896,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_BrassRodAndForgingsMember | 583,940,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_BrassRodAndForgingsMember
OEM Components, Tube & Assemblies [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 345,991,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OemComponentsTubeAndAssembliesMember | 337,772,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OemComponentsTubeAndAssembliesMember | 335,461,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OemComponentsTubeAndAssembliesMember
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 345,991,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OemComponentsTubeAndAssembliesMember | 337,772,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OemComponentsTubeAndAssembliesMember | 335,461,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OemComponentsTubeAndAssembliesMember
Valves and Plumbing Specialties [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 262,504,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_ValvesAndPlumbingSpecialtiesMember | 239,822,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_ValvesAndPlumbingSpecialtiesMember | 231,278,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_ValvesAndPlumbingSpecialtiesMember
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 262,504,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_ValvesAndPlumbingSpecialtiesMember | 239,822,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_ValvesAndPlumbingSpecialtiesMember | 231,278,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_ValvesAndPlumbingSpecialtiesMember
Other [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 55,583,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OtherProductsMember | 54,944,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OtherProductsMember | 52,434,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OtherProductsMember
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 55,583,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OtherProductsMember | 54,944,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OtherProductsMember | 52,434,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = mli_OtherProductsMember
Plumbing and Refrigeration Segment [Member] | Reportable Segments [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 1,416,701,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 1,225,306,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 1,238,230,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 1,416,701,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 1,225,306,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 1,238,230,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
Cost of goods sold |  |  | 1,215,282,000 us-gaap_CostOfGoodsSold / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 1,043,059,000 us-gaap_CostOfGoodsSold / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 1,060,755,000 us-gaap_CostOfGoodsSold / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
Depreciation and amortization |  |  | 19,613,000 us-gaap_OtherDepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 17,117,000 us-gaap_OtherDepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 16,513,000 us-gaap_OtherDepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
Selling, general, and administrative expense |  |  | 87,539,000 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 85,471,000 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 75,448,000 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
Litigation settlement |  |  |  |  | 0 us-gaap_LitigationSettlementAmount / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
Insurance settlement |  |  |  | (103,895,000)us-gaap_GainOnBusinessInterruptionInsuranceRecovery / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | (1,500,000)us-gaap_GainOnBusinessInterruptionInsuranceRecovery / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
(Gain) loss on disposal of assets |  |  | (6,259,000)us-gaap_GainLossOnDispositionOfAssets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | (39,765,000)us-gaap_GainLossOnDispositionOfAssets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember |
Impairment charges |  |  |  | 4,173,000 us-gaap_AssetImpairmentCharges / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember |
Severance |  |  | 7,296,000 us-gaap_SeveranceCosts1 / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember |  | 0 us-gaap_SeveranceCosts1 / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
Operating income |  |  | 93,230,000 us-gaap_OperatingIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 219,146,000 us-gaap_OperatingIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 87,014,000 us-gaap_OperatingIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
Expenditures for long-lived assets |  |  | 55,098,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 47,222,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 24,030,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
Segment assets | 664,784,000 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember |  | 664,784,000 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 625,371,000 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember | 531,429,000 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_PlumbingAndRefrigerationSegmentMember
OEM Segment [Member] | Reportable Segments [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Proforma net sales |  |  | 959,914,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 947,784,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 974,606,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
Summary of segment information [Abstract] |  |  |  |  |
Proforma net sales |  |  | 959,914,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 947,784,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 974,606,000 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
Cost of goods sold |  |  | 840,823,000 us-gaap_CostOfGoodsSold / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 833,518,000 us-gaap_CostOfGoodsSold / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 866,404,000 us-gaap_CostOfGoodsSold / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
Depreciation and amortization |  |  | 11,919,000 us-gaap_OtherDepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 13,025,000 us-gaap_OtherDepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 13,435,000 us-gaap_OtherDepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
Selling, general, and administrative expense |  |  | 21,458,000 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 24,479,000 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 27,680,000 us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
Litigation settlement |  |  |  |  | 0 us-gaap_LitigationSettlementAmount / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
Insurance settlement |  |  |  | 0 us-gaap_GainOnBusinessInterruptionInsuranceRecovery / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 0 us-gaap_GainOnBusinessInterruptionInsuranceRecovery / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
(Gain) loss on disposal of assets |  |  | 0 us-gaap_GainLossOnDispositionOfAssets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 0 us-gaap_GainLossOnDispositionOfAssets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember |
Impairment charges |  |  |  | 131,000 us-gaap_AssetImpairmentCharges / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember |
Severance |  |  | 0 us-gaap_SeveranceCosts1 / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember |  | 0 us-gaap_SeveranceCosts1 / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
Operating income |  |  | 85,714,000 us-gaap_OperatingIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 76,631,000 us-gaap_OperatingIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 67,087,000 us-gaap_OperatingIncomeLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
Expenditures for long-lived assets |  |  | 10,788,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 14,845,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 24,137,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
Segment assets | 313,245,000 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember |  | 313,245,000 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 305,052,000 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember | 290,058,000 us-gaap_Assets / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = mli_OemSegmentMember
General Corporate [Member] |  |  |  |  |
Summary of segment information [Abstract] |  |  |  |  |
Expenditures for long-lived assets |  |  | 400,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mli_GeneralCorporateMember | 3,253,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mli_GeneralCorporateMember | 17,290,000 us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_StatementBusinessSegmentsAxis = mli_GeneralCorporateMember
Segment assets | $ 350,067,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mli_GeneralCorporateMember |  | $ 350,067,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mli_GeneralCorporateMember | $ 317,344,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mli_GeneralCorporateMember | $ 282,668,000 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = mli_GeneralCorporateMember

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