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CONSOLIDATED STATEMENTS OF CAPITAL STOCK AND LONG-TERM DEBT (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Common Stock, No Par Value	$ 148,668us-gaap_CommonStockValue	$ 146,185us-gaap_CommonStockValue
Retained Earnings	48,623us-gaap_RetainedEarningsAccumulatedDeficit	42,560us-gaap_RetainedEarningsAccumulatedDeficit
TOTAL COMMON EQUITY	197,291msex_TotalCommonEquity	188,745msex_TotalCommonEquity
TOTAL PREFERRED STOCK	2,436us-gaap_PreferredStockValue	2,886us-gaap_PreferredStockValue
SUBTOTAL LONG-TERM DEBT	140,029us-gaap_LongTermDebt	133,112us-gaap_LongTermDebt
Add: Premium on Issuance of Long-term Debt	1,920us-gaap_DebtInstrumentUnamortizedPremium	2,072us-gaap_DebtInstrumentUnamortizedPremium
Less: Current Portion of Long-term Debt	(5,910)us-gaap_LongTermDebtCurrent	(5,386)us-gaap_LongTermDebtCurrent
TOTAL LONG-TERM DEBT	136,039us-gaap_LongTermDebtNoncurrent	129,798us-gaap_LongTermDebtNoncurrent
Amortizing Secured Note, due December 20, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	1,825us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = us-gaap_SecuredDebtMember	2,005us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = us-gaap_SecuredDebtMember
Amortizing Secured Note, due May 19, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	5,635us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt1Member	6,055us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt1Member
Amortizing Secured Note, due August 25, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	4,387us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt2Member	4,667us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt2Member
Amortizing Secured Note, due September 19, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	4,667us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt3Member	4,947us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt3Member
State Revolving Trust Note, due December 31, 2022 [Member]
SUBTOTAL LONG-TERM DEBT	421us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNoteMember	465us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNoteMember
State Revolving Trust Note, due May 1, 2025 [Member]
SUBTOTAL LONG-TERM DEBT	2,463us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote1Member	2,654us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote1Member
State Revolving Trust Note, due March 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	506us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote9Member	541us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote9Member
State Revolving Trust Note, due January 25, 2027 [Member]
SUBTOTAL LONG-TERM DEBT	536us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote2Member	569us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote2Member
State Revolving Trust Note, due December 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	697us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote3Member	742us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote3Member
State Revolving Trust Bond 4.00% to 5.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	299us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustBondMember	343us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustBondMember
State Revolving Trust Bond 0.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	241us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustBond1Member	281us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustBond1Member
State Revolving Trust Note, due July 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	313us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote4Member	330us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote4Member
State Revolving Trust Note, due January 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	104us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote5Member	110us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote5Member
State Revolving Trust Note, due August 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	1,115us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote6Member	467us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote6Member
Amortizing Secured Note, due April 20, 2029 [Member]
SUBTOTAL LONG-TERM DEBT	4,999us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt4Member	5,348us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt4Member
Amortizing Secured Note 7.05%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	3,771us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt5Member	4,021us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt5Member
Amortizing Secured Note 5.69%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	7,735us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt6Member	8,248us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt6Member
Amortizing Secured Note, due April 20, 2040 [Member]
SUBTOTAL LONG-TERM DEBT	8,000us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_SecuredDebt7Member
State Revolving Trust Note, due July 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	2,411us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote7Member	2,515us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote7Member
State Revolving Trust Note, due November 30, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	1,276us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote8Member	1,333us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_StateRevolvingTrustNote8Member
First Mortgage Bonds - Series X [Member]
SUBTOTAL LONG-TERM DEBT	215us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage1Member	268us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage1Member
First Mortgage Bonds - Series Y [Member]
SUBTOTAL LONG-TERM DEBT	245us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage2Member	300us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage2Member
First Mortgage Bonds - Series Z [Member]
SUBTOTAL LONG-TERM DEBT	559us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage3Member	671us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage3Member
First Mortgage Bonds - Series AA [Member]
SUBTOTAL LONG-TERM DEBT	700us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage4Member	830us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage4Member
First Mortgage Bonds - Series BB [Member]
SUBTOTAL LONG-TERM DEBT	845us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage5Member	965us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage5Member
First Mortgage Bonds - Series CC [Member]
SUBTOTAL LONG-TERM DEBT	1,025us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage6Member	1,145us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage6Member
First Mortgage Bonds - Series EE [Member]
SUBTOTAL LONG-TERM DEBT	3,550us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage8Member	3,968us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage8Member
First Mortgage Bonds - Series FF [Member]
SUBTOTAL LONG-TERM DEBT	4,900us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage9Member	5,335us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage9Member
First Mortgage Bonds - Series GG [Member]
SUBTOTAL LONG-TERM DEBT	1,083us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage10Member	1,171us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage10Member
First Mortgage Bonds - Series HH [Member]
SUBTOTAL LONG-TERM DEBT	1,390us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage11Member	1,475us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage11Member
First Mortgage Bonds - Series II [Member]
SUBTOTAL LONG-TERM DEBT	881us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage12Member	971us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage12Member
First Mortgage Bonds - Series JJ [Member]
SUBTOTAL LONG-TERM DEBT	1,090us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage13Member	1,165us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage13Member
First Mortgage Bonds - Series KK [Member]
SUBTOTAL LONG-TERM DEBT	1,255us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage14Member	1,346us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage14Member
First Mortgage Bonds - Series LL [Member]
SUBTOTAL LONG-TERM DEBT	1,435us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage15Member	1,505us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage15Member
First Mortgage Bonds - Series MM [Member]
SUBTOTAL LONG-TERM DEBT	1,537us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage16Member	1,637us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage16Member
First Mortgage Bonds - Series NN [Member]
SUBTOTAL LONG-TERM DEBT	1,755us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage17Member	1,835us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage17Member
First Mortgage Bonds - Series OO [Member]
SUBTOTAL LONG-TERM DEBT	2,559us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage18Member	2,709us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage18Member
First Mortgage Bonds - Series PP [Member]
SUBTOTAL LONG-TERM DEBT	850us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage19Member	885us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage19Member
First Mortgage Bonds - Series QQ [Member]
SUBTOTAL LONG-TERM DEBT	9,915us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage20Member	9,915us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage20Member
First Mortgage Bonds - Series RR [Member]
SUBTOTAL LONG-TERM DEBT	22,500us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage21Member	22,500us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage21Member
First Mortgage Bonds - Series SS [Member]
SUBTOTAL LONG-TERM DEBT	23,000us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage22Member	23,000us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage22Member
First Mortgage Bonds - Series TT [Member]
SUBTOTAL LONG-TERM DEBT	2,709us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage23Member	2,860us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage23Member
First Mortgage Bonds - Series UU [Member]
SUBTOTAL LONG-TERM DEBT	975us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage24Member	1,015us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage24Member
First Mortgage Bonds - Series VV [Member]
SUBTOTAL LONG-TERM DEBT	2,720us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage25Member
First Mortgage Bonds - Series WW [Member]
SUBTOTAL LONG-TERM DEBT	935us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = msex_FirstMortgage26Member
Convertible Preferred Stock $7.00 Series
TOTAL PREFERRED STOCK	1,007us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = us-gaap_ConvertiblePreferredStockMember	1,457us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = us-gaap_ConvertiblePreferredStockMember
Convertible Preferred Stock $8.00 Series [Member]
TOTAL PREFERRED STOCK	349us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStock1Member	349us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = msex_ConvertiblePreferredStock1Member
Nonredeemable Preferred Stock $7.00 Series
TOTAL PREFERRED STOCK	80us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = us-gaap_NonredeemablePreferredStockMember	80us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = us-gaap_NonredeemablePreferredStockMember
Nonredeemable Preferred Stock $4.75 Series [Member]
TOTAL PREFERRED STOCK	$ 1,000us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = msex_NonredeemablePreferredStock1Member	$ 1,000us-gaap_PreferredStockValue / us-gaap_StatementClassOfStockAxis = msex_NonredeemablePreferredStock1Member

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