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Rate and Regulatory Matters (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)
Tidewater Utilities Inc [Member]
Regulatory Liabilities [Line Items]
Projected annual revenue	$ 300

X

- Definition

The projected annual revenue from new water operations.

+ References

No definition available.

+ Details

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Namespace Prefix:	msex_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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

X

- Details

Name:	dei_LegalEntityAxis=msex_TidewaterUtilitiesIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: