XML 61 R52.htm IDEA: XBRL DOCUMENT
v3.25.3

Regulatory Matters - Additional Information (Detail) - USD ($) | Jul. 01, 2025 | May 01, 2025 | Feb. 28, 2025 | Dec. 09, 2024 | Nov. 26, 2024 | Nov. 01, 2024 | Oct. 04, 2024 | Sep. 11, 2024 | Jul. 18, 2024 | Jun. 28, 2024 | May 01, 2024 | Sep. 20, 2023 | Aug. 17, 2023 | Jul. 26, 2023 | Jul. 20, 2022 | Jun. 08, 2022 | Oct. 31, 2025 | Apr. 15, 2025 | Oct. 31, 2024 | May 31, 2024 | May 31, 2023
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested annual increase in rates |  |  |  |  |  |  |  |  |  |  | $ 2,100,000 |  |  |  |  |  |  |  |  |  |
Northern Utilities Inc |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved annual increase in rates |  |  |  |  |  |  |  |  |  |  |  | $ 7,600,000 |  |  |  |  |  |  |  |  |
Return on equity |  |  |  |  |  |  |  |  |  |  |  | 9.35% |  |  |  |  |  |  |  |  |
Equity ratio |  |  |  |  |  |  |  |  |  |  |  | 52.01% |  |  |  |  |  |  |  |  |
Weighted average cost of capital |  |  |  |  |  |  |  |  |  |  |  | 7.22% |  |  |  |  |  |  |  |  |
Northern Utilities Inc | Settlement Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved annual increase in rates |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6,100,000 |  |  |  |  |  |
Northern Utilities Inc | New Hampshire |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of approved return on equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.30% |  |  |  |  |  |
Percentage of approved return on equity, reflecting on equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 52.00% |  |  |  |  |  |
Percentage of approved return on equity, reflecting on debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 48.00% |  |  |  |  |  |
Requested annual increase in rates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,600,000 |  |  |  |  |
Unitil Energy Systems Inc |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
percent above present rates | 3.70% | 7.30% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved annual increase in rates |  | $ 18,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities approved increase amount of annual revenue to recover eligible capital investments | $ 7,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fitchburg Gas and Electric Light Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual revenue |  |  |  |  |  | $ 500,000 |  | $ 3,500,000 |  |  |  |  |  | $ 3,100,000 |  |  |  |  |  |  |
Percentage of approved return on equity |  |  |  |  |  |  |  |  |  | 9.40% |  |  |  |  |  |  |  |  |  |  |
Percentage of approved return on equity, reflecting on equity |  |  |  |  |  |  |  |  |  | 52.00% |  |  |  |  |  |  |  |  |  |  |
Percentage of approved return on equity, reflecting on debt |  |  |  |  |  |  |  |  |  | 48.00% |  |  |  |  |  |  |  |  |  |  |
Increase in cost |  |  |  |  |  |  |  |  |  | $ 2,200,000 |  |  |  |  |  |  |  |  |  |  |
Accumulated deferred income taxes |  |  |  | $ 1,400,000 | $ 100,000 |  |  |  | $ 1,400,000 |  |  |  |  |  |  |  |  |  |  |  |
Fitchburg Gas and Electric Light Company | July 1, 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved annual increase in rates |  |  |  |  |  |  |  |  |  | $ 4,700,000 |  |  | $ 6,800,000 |  |  |  |  |  |  |  |
Fitchburg Gas Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual revenue |  |  |  |  |  |  |  |  |  |  |  |  | 4,200,000 |  |  |  |  |  |  |  |
Percentage of approved return on equity |  |  |  |  |  |  |  |  |  | 9.40% |  |  |  |  |  |  |  |  |  |  |
Percentage of approved return on equity, reflecting on equity |  |  |  |  |  |  |  |  |  | 52.00% |  |  |  |  |  |  |  |  |  |  |
Percentage of approved return on equity, reflecting on debt |  |  |  |  |  |  |  |  |  | 48.00% |  |  |  |  |  |  |  |  |  |  |
Approved annual increase in rates |  |  |  |  |  |  |  |  |  | $ 10,100,000 |  |  |  |  |  |  |  |  |  |  |
Increase in cost |  |  |  |  |  |  |  |  |  | $ 4,900,000 |  |  |  |  |  |  |  |  |  |  |
Accumulated deferred income taxes |  |  |  | 1,400,000 |  |  |  |  | $ 1,400,000 |  |  |  |  |  |  |  |  |  |  |  |
Fitchburg Gas Company | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual revenue |  |  |  |  |  |  |  |  |  |  |  |  | $ 6,700,000 |  |  |  |  |  |  |  |
Granite State |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual revenue |  |  |  |  |  |  | $ 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fitchburg - Grid Modernization |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets approved increase in revenue due to be recovered |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,400,000 |  | $ 1,300,000 | $ 1,000,000
Fitchburg Performance Base Rate Adjustment Electric |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual revenue |  |  | $ 1,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fitchburg Performance Base Rate Adjustment Gas |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual revenue |  |  | $ 700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fitchburg Gas System Enhancement Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets approved increase in revenue due to be recovered |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5,400,000 |  | $ 3,500,000 |  |
Gas Division [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated deferred income taxes |  |  |  | (600,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Division [Member] | Fitchburg Gas and Electric Light Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated deferred income taxes |  |  |  | (600,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric Division [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated deferred income taxes |  |  |  | (800,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric Division [Member] | Fitchburg Gas and Electric Light Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated deferred income taxes |  |  |  | $ (800,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition The increase (decrease) during the reporting period in the account that represents the temporary difference that results from Income or Loss that is recognized for accounting purposes but not for tax purposes and vice versa. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (a) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 + Details
Name: | us-gaap_IncreaseDecreaseInDeferredIncomeTaxes
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in unrecovered fuel costs for a regulated utility company. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (a) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 + Details
Name: | us-gaap_IncreaseDecreaseInRegulatoryClauseRevenue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of public utility's approved debt to capital, including debt and equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedDebtCapitalStructurePercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of public utility's approved equity to capital, including debt and equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedEquityCapitalStructurePercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
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 Percentage of public utility's approved return on equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of public utility's requested equity to capital, including debt and equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedEquityCapitalStructurePercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Percentage of public utility's requested return on equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedReturnOnEquityPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
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_RegulatoryAssetLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478742/980-340-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 55 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478098/980-340-55-2 + Details
Name: | us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Increase Decrease Transfer Cost Amount + References No definition available. + Details
Name: | utl_IncreaseDecreaseTransferCostAmount
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Public utilities approved increase amount of annual revenue to recover eligible capital investments + References No definition available. + Details
Name: | utl_PublicUtilitiesApprovedIncreaseAmountOfAnnualRevenueToRecoverEligibleCapitalInvestments
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Public Utility Rate Change Percentage + References No definition available. + Details
Name: | utl_PublicUtilityRateChangePercentage
Namespace Prefix: | utl_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted Average Cost Of Capital + References No definition available. + Details
Name: | utl_WeightedAverageCostOfCapital
Namespace Prefix: | utl_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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

X
- Details
Name: | utl_AgreementAxis=utl_SettlementAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=stpr_NH
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | us-gaap_TaxPeriodAxis=utl_JulyFirstTwoThousandAndTwentyFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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

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

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

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=utl_GasDivisionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=utl_ElectricDivisionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |