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CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
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Consolidated Statements Of Cash Flows Parenthetical |  |  |
Allowance for Funds Used During Construction | $ 175 | $ 299 | $ 359

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- Definition AFUDC is a component of construction costs representing net cost of borrowed funds and a reasonable rate on other funds used during the period of construction. + References No definition available. + Details
Name: | MSEX_AllowanceForFundsUsedDuringConstruction
Namespace Prefix: | MSEX_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | MSEX_StatementsOfCashFlowsParentheticalAbstract
Namespace Prefix: | MSEX_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration