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v3.20.4

CUSTOMER INFORMATION (Details) - customer | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Customer Concentration Risk | Net sales |  |  |
Concentration Risk [Line Items] |  |  |
Number of customer | 0 | 0 | 0

X
- Definition Represents information about customer. + References No definition available. + Details
Name: | mlr_NumberOfCustomer
Namespace Prefix: | mlr_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- 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_ConcentrationRiskLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueNetMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |