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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	40,000,000us-gaap_CommonStockSharesAuthorized	40,000,000us-gaap_CommonStockSharesAuthorized				40,000,000us-gaap_CommonStockSharesAuthorized
Authorized shares under plan	300,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized					300,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Issuance of shares under the DRP	$ 1,493,000us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan	$ 1,653,000us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan	$ 1,587,000us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan
Maximum number of shares authorized for grant	200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant					200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Preferred Stock, Shares Authorized	126,000us-gaap_PreferredStockSharesAuthorized	126,000us-gaap_PreferredStockSharesAuthorized				126,000us-gaap_PreferredStockSharesAuthorized
Preferred Stock, Shares Outstanding	24,000us-gaap_PreferredStockSharesOutstanding	28,000us-gaap_PreferredStockSharesOutstanding				24,000us-gaap_PreferredStockSharesOutstanding
Proceeds from long-term debt borrowing	12,246,000us-gaap_ProceedsFromIssuanceOfLongTermDebt	4,045,000us-gaap_ProceedsFromIssuanceOfLongTermDebt	60,350,000us-gaap_ProceedsFromIssuanceOfLongTermDebt
Long-term debt	140,029,000us-gaap_LongTermDebt	133,112,000us-gaap_LongTermDebt				140,029,000us-gaap_LongTermDebt
Weighted average interest rate	3.99%us-gaap_LongtermDebtWeightedAverageInterestRate	4.23%us-gaap_LongtermDebtWeightedAverageInterestRate				3.99%us-gaap_LongtermDebtWeightedAverageInterestRate
Deobligated principal payments		64,000msex_DeobligatedPrincipalPayments	255,000msex_DeobligatedPrincipalPayments
Other long term debt	50,800,000us-gaap_OtherLongTermDebt	45,000,000us-gaap_OtherLongTermDebt				50,800,000us-gaap_OtherLongTermDebt
Customer advances	21,978,000us-gaap_CustomerAdvancesForConstruction	21,837,000us-gaap_CustomerAdvancesForConstruction				21,978,000us-gaap_CustomerAdvancesForConstruction
Dividend Reinvestment and Common Stock Purchase Plan [Member]
Schedule of Capitalization [Line Items]
Shares authorized	2,300,000us-gaap_CommonStockSharesAuthorized / us-gaap_ShareRepurchaseProgramAxis = msex_DividendReinvestmentCommonStockPurchasePlanMember				3,000,000us-gaap_CommonStockSharesAuthorized / us-gaap_ShareRepurchaseProgramAxis = msex_DividendReinvestmentCommonStockPurchasePlanMember	2,300,000us-gaap_CommonStockSharesAuthorized / us-gaap_ShareRepurchaseProgramAxis = msex_DividendReinvestmentCommonStockPurchasePlanMember
Dividend Reinvestment & Common Stock Purchase Plan, cumulative shares	2,200,000msex_DividendReinvestmenPlanSharesIssuedCumulative / us-gaap_ShareRepurchaseProgramAxis = msex_DividendReinvestmentCommonStockPurchasePlanMember
Outside Director Stock Compensation Plan [Member]
Schedule of Capitalization [Line Items]
Authorized shares under plan	76,915us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember					76,915us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember
Common stock granted and issued under plan	5,082us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember	5,432us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember	5,768us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember
Maximum number of shares authorized for grant	100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember					100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember
Preferred stock dividends in arrears	0us-gaap_PreferredStockAmountOfPreferredDividendsInArrears / us-gaap_PlanNameAxis = msex_OutsideDirectorStockCompensationPlanMember
Convertible Preferred Stock $7.00 Series [Member]
Schedule of Capitalization [Line Items]
Convertible preferred stock converted, shares	4,293us-gaap_ConversionOfStockSharesConverted1 / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries7Member
Convertible preferred stock converted, value	500,000us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries7Member
Stock issued upon conversion of convertible preferred stock (shares)	51,516us-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	13.714us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member					13.714us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member
Convertible preferred stock converted, shares				4,000us-gaap_ConversionOfStockSharesConverted1 / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member
Convertible preferred stock converted, value				500,000us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member
Stock issued upon conversion of convertible preferred stock (shares)				54,856us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStockSeries8Member
Tidewater [Member]
Schedule of Capitalization [Line Items]
Loan amount					4,000,000us-gaap_DebtInstrumentFaceAmount / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember				15,000,000us-gaap_DebtInstrumentFaceAmount / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember
Proceeds from long-term debt borrowing					3,000,000us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember	8,000,000us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember
Long-term debt					11,000,000us-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	1,400,000us-gaap_DebtInstrumentFaceAmount / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember					1,400,000us-gaap_DebtInstrumentFaceAmount / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember
Proceeds from long-term debt borrowing							3,800,000us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember	3,900,000us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember
Long-term debt	33,800,000us-gaap_LongTermDebt / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember					33,800,000us-gaap_LongTermDebt / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember
Deobligated principal payments		100,000msex_DeobligatedPrincipalPayments / dei_LegalEntityAxis = msex_NewJerseyEnvironmentalInfrastructureTrustMember	300,000msex_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								2,900,000us-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								1,000,000us-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							2,800,000us-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							900,000us-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	9,800,000us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember					9,800,000us-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	600,000us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember
Long-term debt	1,100,000us-gaap_LongTermDebt / dei_LegalEntityAxis = msex_TidewaterUtilitiesIncMember / us-gaap_LongtermDebtTypeAxis = msex_DelawareStateRevolvingFundMember					1,100,000us-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	$ 55,400,000us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = msex_NewJerseyEconomicDevelopmentAuthorityMember					$ 55,400,000us-gaap_LongTermDebt / us-gaap_LongtermDebtTypeAxis = msex_NewJerseyEconomicDevelopmentAuthorityMember

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Number of shares issued during the period as a result of the conversion of convertible securities.

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