Budgeted construction cost for construction program, next year.

No definition available.

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Namespace Prefix:	msex_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Estimated incremental borrowing rate.

+ References

No definition available.

+ Details

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Namespace Prefix:	msex_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The expiration date of a long-term purchase commitment.

+ References

No definition available.

+ Details

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Namespace Prefix:	msex_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of units of goods that must be purchased within the specified time period of the agreement to avoid penalties or unfavorable effects on pricing, among other adverse consequences.

+ References

No definition available.

+ Details

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

- Definition

Amount of operating lease income from lease payments paid and payable to lessor. Excludes variable lease payments not included in measurement of lease receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 6A
-URI http://asc.fasb.org/extlink&oid=124502072&loc=SL77927221-108306

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124258985&loc=SL77919372-209981

+ Details

Name:	us-gaap_OperatingLeaseLeaseIncomeLeasePayments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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_PurchaseCommitmentExcludingLongtermCommitmentLineItems
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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Details

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- Details

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Data Type:	na
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- Details

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Commitments and Contingent Liabilities (Narrative) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) gal	Sep. 30, 2020 USD ($)
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Budgeted construction cost for construction program, 2021 \| $			$ 77.0
Contractual construction agreements \| $			38.0
Rental expenses under operating leases \| $	$ 0.2	$ 0.2	$ 0.6	$ 0.6
Estimated incremental borrowing rate	4.03%		4.03%
NJ Water Supply Authority [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Purchase commitment expiration date of contract			Nov. 30, 2023
Water purchase per commitment \| gal			27
Regulated Water Authority [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Purchase commitment expiration date of contract			Feb. 27, 2026
Water purchase per commitment \| gal			3
City of Dover [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Water purchase per commitment \| gal			15