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Employee Benefit Plans (Details 4) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2013
Pension Benefit Plan |
Expected amortized actuarial Loss | $ 416
Expected amortized prior service cost | 2
Other Benefits Plan |
Expected amortized actuarial Loss | 1,413
Expected amortized prior service cost | $ (1,728)

X
- Definition Expected amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions. + References No definition available. + Details
Name: | msex_ExpectedAmortizedActuarialLoss
Namespace Prefix: | msex_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Expected amount of amortization of the net prior service costs. + References No definition available. + Details
Name: | msex_ExpectedAmortizedPriorServiceCost
Namespace Prefix: | msex_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration