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Organization, Summary of Significant Accounting Policies and Recent Developments (Schedule of AFUDC Rates) (Details) | 12 Months Ended
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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 + Details
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