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Commitments and Contingent Liabilities (Schedule of Purchased Water Costs) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Purchased Water
Treated	$ 2.4msex_CostOfTreatedWater	$ 2.4msex_CostOfTreatedWater	$ 2.4msex_CostOfTreatedWater
Untreated	3.1msex_CostOfUntreatedWater	3.2msex_CostOfUntreatedWater	3.1msex_CostOfUntreatedWater
Total Costs	$ 5.5us-gaap_CostOfPurchasedWater	$ 5.6us-gaap_CostOfPurchasedWater	$ 5.5us-gaap_CostOfPurchasedWater

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- Definition

Refers to cost of treated water during the period.

+ References

No definition available.

+ Details

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- Definition

Refers to cost of untreated water during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	msex_
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X

- Definition

Cost of water purchased, may include any water related assessment. If water is bought on a unit volume basis, would also be considered as commodity costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.2)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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