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Refers to gain (loss) position on fair value of future contracts.

No definition available.

Name:	mli_GainLossOnFairValueOfFutureContracts
Namespace Prefix:	mli_
Data Type:	xbrli:monetaryItemType
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The fair value of the open option contracts Put for the investment.

No definition available.

Name:	mli_OpenOptionContractsPutAtFairValue
Namespace Prefix:	mli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Period related to fixed price sales orders of open future contract.

No definition available.

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

Period related to fixed price purchase orders of open future contract.

No definition available.

Name:	mli_TimePeriodForOpenCopperFutureContractSales
Namespace Prefix:	mli_
Data Type:	xbrli:durationItemType
Balance Type:	na
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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.

No definition available.

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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The fair value of the open option contracts written for the investment.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 5
-Subparagraph (SX 210.12-13(Column G))
-URI http://asc.fasb.org/extlink&oid=120401592&loc=d3e611282-123010

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Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
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Data Type:	na
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