CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements Of Cash Flows Parenthetical
Allowance for Funds Used During Construction	$ 175	$ 299	$ 359

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