XML 64 R52.htm IDEA: XBRL DOCUMENT
v3.23.1

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Aug. 31, 2022 | Dec. 31, 2020 | Mar. 31, 2023 | Mar. 31, 2022 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2017
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Corporate federal income tax |  |  | 21.00% | 21.00% |  |  |  |
Regulatory liability, expected flow back to customers |  |  |  |  |  |  | $ 47.1 |
Regulatory liability, expected pass back to ratepayers |  |  |  |  | $ 1.0 |  |  |
Net Operating Loss Carryforwards Utilized For Income Taxes |  |  |  |  |  | $ 2.4 |  |
Deferred tax assets, operating loss carryforwards, federal |  |  |  |  | $ 2.8 | $ 5.3 |  |
Percentage of employment retention credit |  |  | 50.00% |  |  |  |  |
Employment retention duties capacity |  |  | 100.00% |  |  |  |  |
Percentage of alternate minimum tax | 15.00% |  |  |  |  |  |  |
Adjustment financial statement income | $ 1,000.0 |  |  |  |  |  |  |
Number of years used for calculating adjusted financial statement income | 3 years |  |  |  |  |  |  |
Consolidated Appropriations Act 2021 [Member] |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Percentage of employment retention credit |  | 70.00% |  |  |  |  |  |
Employment retention duties capacity |  | 100.00% |  |  |  |  |  |
Gas Ratepayers | Massachusetts And Maine [Member] |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Regulatory liability, expected flow back to customers |  |  | $ 7.1 |  |  |  |  |
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 https://asc.fasb.org/extlink&oid=121826272&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 https://asc.fasb.org/extlink&oid=121826272&loc=d3e32621-109319 + Details
Name: | us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic
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 https://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(h)(2)) -URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32687-109319 + Details
Name: | us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Adjusted financial statement income. + References No definition available. + Details
Name: | utl_AdjustedFinancialStatementIncome
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Employment Retention Duties Capacity. + References No definition available. + Details
Name: | utl_EmploymentRetentionDutiesCapacity
Namespace Prefix: | utl_
Data Type: | dtr-types:percentItemType
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 Number of years used for calculating adjusted financial statement income. + References No definition available. + Details
Name: | utl_NumberOfYearsUsedForCalculatingAdjustedFinancialStatementIncome
Namespace Prefix: | utl_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of alternative minimum tax. + References No definition available. + Details
Name: | utl_PercentageOfAlternativeMinimumTax
Namespace Prefix: | utl_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of employment retention credit. + References No definition available. + Details
Name: | utl_PercentageOfEmploymentRetentionCredit
Namespace Prefix: | utl_
Data Type: | dtr-types: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_UnusualOrInfrequentItemAxis=utl_ConsolidatedAppropriationsActTwentyTwentyOneMember
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: | us-gaap_TaxPeriodAxis=us-gaap_TaxYear2018Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |