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Capitalization (Schedule of Carrying Amount and Fair Value of Bonds) (Details) - USD ($) $ in Thousands | Sep. 30, 2022 | Dec. 31, 2021
--- | --- | ---
Carrying Amount [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
FMBs | $ 147,269 | $ 98,828
Fair Value [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
FMBs | $ 139,285 | $ 107,781

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- Definition Represents the aggregate of the first mortgage bonds reported on the balance sheet at period end measured at fair value by the entity. + References No definition available. + Details
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Namespace Prefix: | msex_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

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- Details
Name: | msex_FairValueByMeasurementsBasisAxis=msex_CarryingReportedAmountFairValueDisclosuresMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | msex_FairValueByMeasurementsBasisAxis=msex_EstimateOfFairValueFairValueDisclosuresMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |