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Capitalization (Narrative) (Details) (USD $) | 12 Months Ended | 1 Months Ended |
--- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Aug. 31, 2013 | Feb. 28, 2015 | Dec. 31, 2014 | May 31, 2014 | May 31, 2013 | Oct. 31, 2014
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Shares authorized | 40,000,000 us-gaap_CommonStockSharesAuthorized | 40,000,000 us-gaap_CommonStockSharesAuthorized |  |  |  | 40,000,000 us-gaap_CommonStockSharesAuthorized |  |  |
Authorized shares under plan | 300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized |  |  |  |  | 300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized |  |  |
Issuance of shares under the DRP | $ 1,493,000 us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan | $ 1,653,000 us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan | $ 1,587,000 us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan |  |  |  |  |  |
Maximum number of shares authorized for grant | 200,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant |  |  |  |  | 200,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant |  |  |
Preferred Stock, Shares Authorized | 126,000 us-gaap_PreferredStockSharesAuthorized | 126,000 us-gaap_PreferredStockSharesAuthorized |  |  |  | 126,000 us-gaap_PreferredStockSharesAuthorized |  |  |
Preferred Stock, Shares Outstanding | 24,000 us-gaap_PreferredStockSharesOutstanding | 28,000 us-gaap_PreferredStockSharesOutstanding |  |  |  | 24,000 us-gaap_PreferredStockSharesOutstanding |  |  |
Proceeds from long-term debt borrowing | 12,246,000 us-gaap_ProceedsFromIssuanceOfLongTermDebt | 4,045,000 us-gaap_ProceedsFromIssuanceOfLongTermDebt | 60,350,000 us-gaap_ProceedsFromIssuanceOfLongTermDebt |  |  |  |  |  |
Long-term debt | 140,029,000 us-gaap_LongTermDebt | 133,112,000 us-gaap_LongTermDebt |  |  |  | 140,029,000 us-gaap_LongTermDebt |  |  |
Weighted average interest rate | 3.99%us-gaap_LongtermDebtWeightedAverageInterestRate | 4.23%us-gaap_LongtermDebtWeightedAverageInterestRate |  |  |  | 3.99%us-gaap_LongtermDebtWeightedAverageInterestRate |  |  |
Deobligated principal payments |  | 64,000 msex_DeobligatedPrincipalPayments | 255,000 msex_DeobligatedPrincipalPayments |  |  |  |  |  |
Other long term debt | 50,800,000 us-gaap_OtherLongTermDebt | 45,000,000 us-gaap_OtherLongTermDebt |  |  |  | 50,800,000 us-gaap_OtherLongTermDebt |  |  |
Customer advances | 21,978,000 us-gaap_CustomerAdvancesForConstruction | 21,837,000 us-gaap_CustomerAdvancesForConstruction |  |  |  | 21,978,000 us-gaap_CustomerAdvancesForConstruction |  |  |
Dividend Reinvestment and Common Stock Purchase Plan [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Shares authorized | 2,300,000 us-gaap_CommonStockSharesAuthorized / us-gaap_ShareRepurchaseProgramAxis = msex_DividendReinvestmentCommonStockPurchasePlanMember |  |  |  | 3,000,000 us-gaap_CommonStockSharesAuthorized / us-gaap_ShareRepurchaseProgramAxis = msex_DividendReinvestmentCommonStockPurchasePlanMember | 2,300,000 us-gaap_CommonStockSharesAuthorized / us-gaap_ShareRepurchaseProgramAxis = msex_DividendReinvestmentCommonStockPurchasePlanMember |  |  |
Dividend Reinvestment & Common Stock Purchase Plan, cumulative shares | 2,200,000 msex_DividendReinvestmenPlanSharesIssuedCumulative / us-gaap_ShareRepurchaseProgramAxis = msex_DividendReinvestmentCommonStockPurchasePlanMember |  |  |  |  |  |  |  |
Outside Director Stock Compensation Plan [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Authorized shares under plan | 76,915 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember |  |  |  |  | 76,915 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember |  |  |
Common stock granted and issued under plan | 5,082 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember | 5,432 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember | 5,768 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember |  |  |  |  |  |
Maximum number of shares authorized for grant | 100,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember |  |  |  |  | 100,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember |  |  |
Preferred stock dividends in arrears | 0 us-gaap_PreferredStockAmountOfPreferredDividendsInArrears / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember |  |  |  |  |  |  |  |
Convertible Preferred Stock $7.00 Series [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Convertible preferred stock converted, shares | 4,293 us-gaap_ConversionOfStockSharesConverted1 / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries7Member |  |  |  |  |  |  |  |
Convertible preferred stock converted, value | 500,000 us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries7Member |  |  |  |  |  |  |  |
Stock issued upon conversion of convertible preferred stock (shares) | 51,516 us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries7Member |  |  |  |  |  |  |  |
Percentage of stock that may be redeemed in a given calander year | 10.00%msex_PercentageOfStockThatMayBeRedeemedInGivenCalanderYear / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries7Member |  |  |  |  | 10.00%msex_PercentageOfStockThatMayBeRedeemedInGivenCalanderYear / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries7Member |  |  |
Convertible Preferred Stock $8.00 Series [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Shares issued upon conversion | 13.714 us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member |  |  |  |  | 13.714 us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member |  |  |
Convertible preferred stock converted, shares |  |  |  | 4,000 us-gaap_ConversionOfStockSharesConverted1 / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member |  |  |  |  |
Convertible preferred stock converted, value |  |  |  | 500,000 us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member |  |  |  |  |
Stock issued upon conversion of convertible preferred stock (shares) |  |  |  | 54,856 us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member |  |  |  |  |
Tidewater [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Loan amount |  |  |  |  | 4,000,000 us-gaap_DebtInstrumentFaceAmount / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember |  |  |  | 15,000,000 us-gaap_DebtInstrumentFaceAmount / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember
Proceeds from long-term debt borrowing |  |  |  |  | 3,000,000 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember | 8,000,000 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember |  |  |
Long-term debt |  |  |  |  | 11,000,000 us-gaap_LongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember |  |  |  |
Interest reate |  |  |  |  | 4.46%us-gaap_DebtInstrumentInterestRateStatedPercentage / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember |  |  |  |
Maturity date | Apr. 01, 2040 |  |  |  |  |  |  |  |
New Jersey Environmental Infrastructure Trust [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Loan amount | 1,400,000 us-gaap_DebtInstrumentFaceAmount / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember |  |  |  |  | 1,400,000 us-gaap_DebtInstrumentFaceAmount / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember |  |  |
Proceeds from long-term debt borrowing |  |  |  |  |  |  | 3,800,000 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember | 3,900,000 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember |
Long-term debt | 33,800,000 us-gaap_LongTermDebt / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember |  |  |  |  | 33,800,000 us-gaap_LongTermDebt / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember |  |  |
Deobligated principal payments |  | 100,000 msex_DeobligatedPrincipalPayments / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember | 300,000 msex_DeobligatedPrincipalPayments / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember |  |  |  |  |  |
First Mortgage Bonds - Series TT [Member] | New Jersey Environmental Infrastructure Trust [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Issuance of series bonds |  |  |  |  |  |  |  | 2,900,000 us-gaap_ProceedsFromIssuanceOfFirstMortgageBond / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage23Member |
Interest reate |  |  |  |  |  |  |  | 0.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage23Member |
Maturity date |  |  |  |  |  |  |  | Aug. 01, 2032 |
First Mortgage Bonds - Series UU [Member] | New Jersey Environmental Infrastructure Trust [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Issuance of series bonds |  |  |  |  |  |  |  | 1,000,000 us-gaap_ProceedsFromIssuanceOfFirstMortgageBond / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage24Member |
Interest rate, minimum |  |  |  |  |  |  |  | 3.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage24Member |
Interest rate, maximum |  |  |  |  |  |  |  | 3.25%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage24Member |
Maturity date |  |  |  |  |  |  |  | Aug. 01, 2032 |
First Mortgage Bonds - Series VV [Member] | New Jersey Environmental Infrastructure Trust [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Issuance of series bonds |  |  |  |  |  |  | 2,800,000 us-gaap_ProceedsFromIssuanceOfFirstMortgageBond / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage25Member |  |
Interest reate |  |  |  |  |  |  | 0.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage25Member |  |
Maturity date |  |  |  |  |  |  | Aug. 01, 2033 |  |
First Mortgage Bonds - Series WW [Member] | New Jersey Environmental Infrastructure Trust [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Issuance of series bonds |  |  |  |  |  |  | 900,000 us-gaap_ProceedsFromIssuanceOfFirstMortgageBond / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage26Member |  |
Interest rate, minimum |  |  |  |  |  |  | 3.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage26Member |  |
Interest rate, maximum |  |  |  |  |  |  | 5.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember / us-gaap_LongtermDebtTypeAxis = msex_FirstMortgage26Member |  |
Maturity date |  |  |  |  |  |  | Aug. 01, 2033 |  |
Delaware State Revolving Fund [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Long-term debt | 9,800,000 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember |  |  |  |  | 9,800,000 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember |  |  |
Delaware State Revolving Fund [Member] | Tidewater [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Proceeds from long-term debt borrowing | 600,000 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember |  |  |  |  |  |  |  |
Long-term debt | 1,100,000 us-gaap_LongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember |  |  |  |  | 1,100,000 us-gaap_LongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember |  |  |
Interest reate | 3.45%us-gaap_DebtInstrumentInterestRateStatedPercentage / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember |  |  |  |  | 3.45%us-gaap_DebtInstrumentInterestRateStatedPercentage / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember |  |  |
Maturity date | Aug. 01, 2031 |  |  |  |  |  |  |  |
New Jersey Economic Development Authority [Member] |  |  |  |  |  |  |  |  |
Schedule of Capitalization [Line Items] |  |  |  |  |  |  |  |  |
Long-term debt | $ 55,400,000 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = msex_NewJerseyEconomicDevelopmentAuthorityMember |  |  |  |  | $ 55,400,000 us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = msex_NewJerseyEconomicDevelopmentAuthorityMember |  |  |

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