CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011
Condensed Consolidated Statements Of Cash Flows Parenthetical
Allowance for Funds Used During Construction	$ 141	$ 221

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.

No definition available.

Name:	MSEX_AllowanceForFundsUsedDuringConstruction
Namespace Prefix:	MSEX_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant