Commitments and Contingencies - Additional Information (Details) $ in Millions		9 Months Ended
Oct. 05, 2016 individual	Sep. 30, 2017 USD ($)
Loss Contingencies [Line Items]
Term of guarantees		1 year
Payments required to be made under guarantees, maximum \| $		$ 8.4
Equal Employment Opportunity Commission Matter [Member]
Loss Contingencies [Line Items]
Number of identified individuals	20
Number of unidentified individuals	150

Refers to identified class of individuals during the period.

No definition available.

Name:	mli_NumberOfIdentifiedClassIndividuals
Namespace Prefix:	mli_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Refers to unidentified class of individuals during the period.

+ References

No definition available.

+ Details

Name:	mli_NumberOfUnidentifiedClassIndividuals
Namespace Prefix:	mli_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the term of guarantees.

+ References

No definition available.

+ Details

Name:	mli_TermOfGuarantees
Namespace Prefix:	mli_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=mli_EqualEmploymentOpportunityCommissionMatterMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: