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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

X

- 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

Name:	msex_FirstMortgageBondsFairValueDisclosure
Namespace Prefix:	msex_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

X

- Details

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

X

- Details

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