Capitalization (Schedule of Carrying Amount and Fair Value of Bonds) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Carrying amount [Member]
First Mortgage Bonds	$ 88,628	$ 87,471
SRF Bonds	540	625
Fair value [Member]
First Mortgage Bonds	88,532	79,733
SRF Bonds	$ 542	$ 628

Represents the aggregate of the state revolving fund reported on the balance sheet at period end measured at fair value by the entity.

No definition available.

Name:	msex_StateRevolvingFundBondsFairValueDisclosure
Namespace Prefix:	msex_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant