Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Jul. 30, 2021
Document And Entity Information [Abstract]
Document Type	10-Q
Entity Central Index Key	0000066004
Document Period End Date	Jun. 30, 2021
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	0-422
Entity Registrant Name	MIDDLESEX WATER COMPANY
Entity Incorporation State Country Code	NJ
Entity Tax Identification Number	22-1114430
Entity Address, Address Line One	485C Route One South
Entity Address, City or Town	Iselin
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	08830
City Area Code	732
Local Phone Number	634-1500
Title of 12(b) Security	Common Stock
Trading Symbol	MSEX
Name of Exchange on which Security is Registered	NASDAQ
Entity Reporting Status Current	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		17,490,561