XML 66 R54.htm IDEA: XBRL DOCUMENT v3.23.3

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2022	Dec. 31, 2020	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	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					$ 1.3
Net Operating Loss Carryforwards Utilized For Income Taxes					1.4
Deferred tax assets, operating loss carryforwards, federal					4.4
Federal tax credit carryforward					0.2
Federal tax credits					$ 1.7
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			$ 8.5
Tax Year 2018
Income Taxes [Line Items]
Corporate federal income tax						21.00%	21.00%

X

- Definition

Amount of current federal tax expense (benefit) attributable to income (loss) from continuing operations. Includes, but is not limited to, current national tax expense (benefit) for non-US (United States of America) jurisdiction.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(1)(Note 1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-SubTopic 10
-Topic 740
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-9

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.7)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

+ Details

Name:	us-gaap_CurrentFederalTaxExpenseBenefit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-6

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-8

+ 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
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-12

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.Fact.4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

+ 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

Federal Tax Credits to Offset Current Taxes

+ References

No definition available.

+ Details

Name:	utl_FederalTaxCreditsToOffsetCurrentTaxes
Namespace Prefix:	utl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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: