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CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY [Abstract]
Conversion of Convertible Preferred Stock Value Per Share	$ 7.00msex_ConversionOfConvertiblePreferredStockValuePerShare	$ 8.00msex_ConversionOfConvertiblePreferredStockValuePerShare

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- Definition

Refers to per share value of conversion of convertible preferred stock.

+ References

No definition available.

+ Details

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Namespace Prefix:	msex_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

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- Details

Name:	us-gaap_StatementOfStockholdersEquityAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration