XML 84 R66.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Employee Benefit Plans - Schedule of Fair Value of Plan Assets (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | --- | ---
Pension Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | $ 98,648 | $ 92,346 | $ 84,828
Pension Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 98,648 | 92,346 |
Pension Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Pension Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Other Benefits Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 53,027 | 48,352 |
Other Benefits Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 35,522 | 30,866 |
Other Benefits Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 17,505 | 17,486 |
Other Benefits Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Mutual Funds [Member] | Pension Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 31,187 | 71,236 |
Mutual Funds [Member] | Pension Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 31,187 | 71,236 |
Mutual Funds [Member] | Pension Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Mutual Funds [Member] | Pension Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Mutual Funds [Member] | Other Benefits Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 34,545 | 29,437 |
Mutual Funds [Member] | Other Benefits Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 34,545 | 29,437 |
Mutual Funds [Member] | Other Benefits Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Mutual Funds [Member] | Other Benefits Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Money Market Funds [Member] | Pension Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 293 | 663 |
Money Market Funds [Member] | Pension Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 293 | 663 |
Money Market Funds [Member] | Pension Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Money Market Funds [Member] | Pension Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Money Market Funds [Member] | Other Benefits Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 977 | 1,429 |
Money Market Funds [Member] | Other Benefits Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 977 | 1,429 |
Money Market Funds [Member] | Other Benefits Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Money Market Funds [Member] | Other Benefits Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Common Equity Securities [Member] | Pension Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 195 | 12,544 |
Common Equity Securities [Member] | Pension Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 195 | 12,544 |
Common Equity Securities [Member] | Pension Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Common Equity Securities [Member] | Pension Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Corporate Bonds [Member] | Pension Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 42,974 | 5,091 |
Corporate Bonds [Member] | Pension Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 42,974 | 5,091 |
Corporate Bonds [Member] | Pension Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Corporate Bonds [Member] | Pension Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Agency/US/State/Municipal Debt [Member] | Pension Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 19,041 | 1,854 |
Agency/US/State/Municipal Debt [Member] | Pension Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 19,041 | 1,854 |
Agency/US/State/Municipal Debt [Member] | Pension Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Agency/US/State/Municipal Debt [Member] | Pension Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Agency/US/State/Municipal Debt [Member] | Other Benefits Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 17,505 | 17,486 |
Agency/US/State/Municipal Debt [Member] | Other Benefits Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Agency/US/State/Municipal Debt [Member] | Other Benefits Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 17,505 | 17,486 |
Agency/US/State/Municipal Debt [Member] | Other Benefits Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Sovereign/Non-US Debt [Member] | Pension Plan [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 4,958 | 958 |
Sovereign/Non-US Debt [Member] | Pension Plan [Member] | Level 1 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets | 4,958 | 958 |
Sovereign/Non-US Debt [Member] | Pension Plan [Member] | Level 2 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |
Sovereign/Non-US Debt [Member] | Pension Plan [Member] | Level 3 [Member] |  |  |
Schedule of Fair Value of Plan Assets [Line Items] |  |  |
Fair value of plan assets |  |  |

X
- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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 Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(03) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_DefinedBenefitPlanPlanAssetsCategoryLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=msex_OtherBenefitsPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_MutualFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_ForeignCorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |