Name:	msex_OriginallyFiledBaseWaterRateIncrease
Namespace Prefix:	msex_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The projected annual revenue from new water operations.

+ References

No definition available.

+ Details

Name:	msex_ProjectedAnnualRevenue
Namespace Prefix:	msex_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Refes to purchase of wastewater utility assets.

+ References

No definition available.

+ Details

Name:	msex_PurchaseOfWastewaterUtilityAssets
Namespace Prefix:	msex_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of refund payments made to customers during the period that was previously reported as deferred revenue. Deferred revenue is a liability as of the balance sheet date related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 605

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 13.A.4(a).Q1)

-URI http://asc.fasb.org/extlink&oid=27012821&loc=d3e214044-122780

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 13

-Section A

+ Details

Name:	us-gaap_DeferredRevenueRefundPayments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Net amount of other deferred costs capitalized at the end of the reporting period. Does not include deferred finance costs or deferred acquisition costs of insurance companies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_OtherDeferredCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

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

- Definition

Percentage of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of public utility's approved return on equity.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of public utility's amended requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

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

- Definition

Amount of public utility's requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.24)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_RegulatoryLiabilityNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_RegulatoryAgencyAxis=msex_DelawarePublicServiceCommissionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAgencyAxis=msex_NewJerseyBoardOfPublicUtilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAgencyAxis=msex_PennsylvaniaPublicUtilitiesCommissionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Rate and Regulatory Matters (Narrative) (Details) (USD $)	3 Months Ended	0 Months Ended	1 Months Ended			12 Months Ended	1 Months Ended		0 Months Ended			1 Months Ended				0 Months Ended
	Jun. 30, 2014	Nov. 08, 2013	Jun. 30, 2014	May 31, 2014	Jul. 31, 2012	Dec. 31, 2014	Mar. 31, 2013	Aug. 31, 2012	Jul. 02, 2014	Apr. 19, 2014	Nov. 25, 2013	Jun. 30, 2012	Oct. 31, 2014	Oct. 31, 2013 N	Jun. 30, 2011	Mar. 03, 2012	Dec. 31, 2013
Regulatory Liabilities [Line Items]
Regulatory Liability - Cost of Utility Plant Removal						$ 10,273,000us-gaap_RegulatoryLiabilityNoncurrent											$ 9,639,000us-gaap_RegulatoryLiabilityNoncurrent
Acquisition premiums to be recovered						600,000us-gaap_OtherDeferredCostsNet
New Jersey Board of Public Utilities [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues	4,200,000
New Jersey Board of Public Utilities [Member] \| Middlesex [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues			4,200,000
Originally filed increase in annual operating revenue		10,600,000		3,600,000
Amended filed increase in annual operating revenue		8,100,000
Base rate amount			208,600,000
Return on equity			9.75%
Projected annual revenue						300,000
Increase in base rates revenue per year					8,100,000
Originally filed base water rate increase					11,300,000
New Jersey Board of Public Utilities [Member] \| Pinelands Water and Wastewater [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues							200,000
Originally filed increase in annual operating revenue								300,000
Approved increase in annual operating revenue (percentage)							50.00%
Delaware Public Service Commission [Member] \| Tidewater [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues	800,000											3,900,000
Originally filed increase in annual operating revenue											3,900,000	6,900,000
Approved increase in annual operating revenue (percentage)									6.50%
Amended filed increase in annual operating revenue									2,500,000	800,000
Refund of previously deferred revenues						400,000
Projected annual revenue						100,000
Delaware Public Service Commission [Member] \| TESI [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues												600,000	100,000	200,000
Originally filed increase in annual operating revenue												800,000
Approved increase in annual operating revenue (percentage)													33.50%
Number of customers														600
Purchase of the wastewater utility assets														400,000
Delaware Public Service Commission [Member] \| Southern Shores [Member]
Regulatory Liabilities [Line Items]
Originally filed increase in annual operating revenue															100,000
Pennsylvania Public Utilities Commission [Member] \| Twin Lakes [Member]
Regulatory Liabilities [Line Items]
Originally filed increase in annual operating revenue																$ 100,000