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Organization, Summary of Significant Accounting Policies and Recent Developments (Schedule of AFUDC Rates) (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Middlesex [Member]
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Allowance for Funds Used During Construction Rates	7.03%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate / dei_LegalEntityAxis = msex_MiddlesexWaterCompanyMember	7.34%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate / dei_LegalEntityAxis = msex_MiddlesexWaterCompanyMember	7.34%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate / dei_LegalEntityAxis = msex_MiddlesexWaterCompanyMember
Tidewater [Member]
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Allowance for Funds Used During Construction Rates	7.91%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember	7.91%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember	7.91%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember

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- Definition

Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 835

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 835

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430

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