XML 63 R49.htm IDEA: XBRL DOCUMENT
v3.20.2

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions | 1 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Mar. 31, 2020 | Dec. 31, 2017 | Sep. 30, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Jan. 01, 2020 | Sep. 30, 2019
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Regulatory Liability |  |  | $ 55.3 | $ 54.0 |  |  |  | $ 61.1
Regulatory liability, expected flow back to customers |  |  | 47.1 |  | $ 48.9 |  |  |
Regulatory liability, expected pass back to ratepayers |  |  | 0.2 | 0.3 |  |  |  |
Net Operating Loss Carryforwards Utilized For Income Taxes |  |  |  |  | 8.2 |  |  |
Deferred tax assets, operating loss carryforwards, federal |  |  | 2.7 |  |  |  |  |
Alternative minimum tax credit carryforwards |  |  | 0.9 |  |  |  | $ 0.1 |
Additional Alternative minimum tax credit carryforwards |  |  | $ 1.9 |  |  |  |  |
Percentage of employment retention credit |  |  | 50.00% |  |  |  |  |
Employment retention duties capacity |  |  | 100.00% |  |  |  |  |
Employment tax expense |  |  | $ 0.6 |  |  |  |  |
Reconciling Mechanisms |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Regulatory liability, expected pass back to ratepayers |  |  |  |  |  | $ 1.8 |  |
Net Operating Loss Carryforward Assets |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Regulatory liability, expected pass back to ratepayers |  |  |  |  | $ 2.0 |  |  |
Income Tax Related Liabilities |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Regulatory Liability |  | $ 48.9 | 45.8 | $ 47.6 |  | $ 48.9 |  | $ 47.6
Electric Ratepayers | Fitchburg Gas and Electric Light Company |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Regulatory liability, expected flow back to customers |  |  | 10.1 |  |  |  |  |
Gas Ratepayers | Massachusetts And Maine [Member] |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Regulatory liability, expected flow back to customers |  |  | 1.6 |  |  |  |  |
Gas Ratepayers | Fitchburg Gas and Electric Light Company |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Regulatory liability, expected flow back to customers |  |  | $ 10.4 |  |  |  |  |
Gas Ratepayers | Northern Utilities Inc |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Regulatory liability, expected flow back to customers | $ 12.3 |  |  |  |  |  |  |
Average Rate Assumption Method estimated flow back period | 20 years |  |  |  |  |  |  |
Tax Year 2018 |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Corporate federal income tax |  | 21.00% | 21.00% |  |  |  |  |

X
- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible domestic operating loss carryforwards. Excludes state and local operating loss carryforwards. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319 + Details
Name: | us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible alternative minimum tax credit carryforwards. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319 + Details
Name: | us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 6.I.Fact.4) -URI http://asc.fasb.org/extlink&oid=116825942&loc=d3e330036-122817 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
Name: | us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
Name: | us-gaap_RegulatoryLiabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Deferred tax assets, tax credit carryforwards, additional alternative minimum tax. + References No definition available. + Details
Name: | utl_DeferredTaxAssetsTaxCreditCarryforwardsAdditionalAlternativeMinimumTax
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Employment retention duties capacity. + References No definition available. + Details
Name: | utl_EmploymentRetentionDutiesCapacity
Namespace Prefix: | utl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Employment tax expense. + References No definition available. + Details
Name: | utl_EmploymentTaxExpense
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Estimated flow back period. + References No definition available. + Details
Name: | utl_EstimatedFlowBackPeriod
Namespace Prefix: | utl_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Income Taxes [Line Items] + References No definition available. + Details
Name: | utl_IncomeTaxesLineItems
Namespace Prefix: | utl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Net operating loss carryforwards utilized for income taxes. + References No definition available. + Details
Name: | utl_NetOperatingLossCarryforwardsUtilizedForIncomeTaxes
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of employment retention credit. + References No definition available. + Details
Name: | utl_PercentageOfEmploymentRetentionCredit
Namespace Prefix: | utl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Regulatory liability recovery refund. + References No definition available. + Details
Name: | utl_RegulatoryLiabilityRecoveryRefund
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Tax Cuts and Jobs Act of 2017 change in tax rate regulatory liability recovery refund. + References No definition available. + Details
Name: | utl_TaxCutsAndJobsActOf2017ChangeInTaxRateRegulatoryLiabilityRecoveryRefund
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_TaxCreditCarryforwardAxis=utl_ReconcilingItemsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_TaxCreditCarryforwardAxis=utl_NetOperatingLossCarryforwardAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryLiabilityAxis=utl_IncomeTaxRelatedLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryLiabilityAxis=utl_ElectricRatePayersMember
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_RegulatoryLiabilityAxis=utl_GasRatePayersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | us-gaap_TaxPeriodAxis=us-gaap_TaxYear2018Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |