XML 41 R28.htm IDEA: XBRL DOCUMENT
v3.20.2

Rate and Regulatory Matters (Details) - USD ($) $ in Millions | 1 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jul. 31, 2019 | Sep. 30, 2020 | Dec. 31, 2019
Delaware Public Service Commission Member |  |  |
Regulatory Liabilities [Line Items] |  |  |
Percentage of consumer price index |  |  | 3.00%
Maturity date |  |  | Dec. 31, 2029
Delaware Public Service Commission Member | Tidewater [Member] |  |  |
Regulatory Liabilities [Line Items] |  |  |
Approved increase in annual operating revenues |  |  | $ 0.5
New Jersey Board Of Public Utilities [Member] | Middlesex [Member] |  |  |
Regulatory Liabilities [Line Items] |  |  |
Approved increase in annual operating revenues |  | $ 0.6 |
Pennsylvania Public Utilities Commissio [Member] | Twin Lakes [Member] |  |  |
Regulatory Liabilities [Line Items] |  |  |
Approved increase in annual operating revenues | $ 0.2 | $ 0.1 |

X
- Definition Percentage of consumer price index. + References No definition available. + Details
Name: | msex_PercentageOfConsumerPriceIndex
Namespace Prefix: | msex_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(2)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
Name: | us-gaap_DebtInstrumentMaturityDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of public utility's approved rate increase (decrease) by regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_RegulatoryLiabilitiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RegulatoryAgencyAxis=msex_DelawarePublicServiceCommissionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=msex_TidewaterMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryAgencyAxis=msex_NewJerseyBoardOfPublicUtilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=msex_MiddlesexMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryAgencyAxis=msex_PennsylvaniaPublicUtilitiesCommissioMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=msex_TwinLakesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |