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