| Cover | Aug. 30, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 30, 2021 |
| Entity File Number | 0-422 |
| Entity Registrant Name | MIDDLESEX WATER COMPANY |
| Entity Central Index Key | 0000066004 |
| Entity Tax Identification Number | 22-1114430 |
| Entity Incorporation, State or Country Code | NJ |
| Entity Address, Address Line One | 485C Route 1 South |
| Entity Address, Address Line Two | Suite 400 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, No Par Value |
| Trading Symbol | MSEX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
