XML 43 R34.htm IDEA: XBRL DOCUMENT v3.25.3

Regulatory Assets (Detail) - USD ($) $ in Millions		Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Regulatory Assets [Line Items]
Regulatory Assets		$ 105.6	$ 112.0	$ 110.8
Less: Current Portion of Regulatory Assets	[1]	60.5	70.1	61.3
Regulatory Assets – noncurrent		45.1	41.9	49.5
Environmental Matters
Regulatory Assets [Line Items]
Regulatory Assets		10.6	9.4	6.3
Other Deferred Charges
Regulatory Assets [Line Items]
Regulatory Assets		12.5	14.1	12.4
Retirement Benefits
Regulatory Assets [Line Items]
Regulatory Assets		19.1	14.4	26.2
Deferred Storm Charges
Regulatory Assets [Line Items]
Regulatory Assets		7.5	8.3	8.9
Income Taxes
Regulatory Assets [Line Items]
Regulatory Assets		0.5	0.4	0.5
Energy Supply and Other Rate Adjustment Mechanisms
Regulatory Assets [Line Items]
Regulatory Assets		$ 55.4	$ 65.4	$ 56.5
[1] Reflects amounts included in the Accrued Revenue on the Company’s Consolidated Balance Sheets.

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

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ 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

+ Details

Name:	us-gaap_RegulatoryAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ 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

+ Details

Name:	us-gaap_RegulatoryAssetsCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ 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

+ Details

Name:	us-gaap_RegulatoryAssetsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=utl_EnvironmentalMattersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=utl_OtherDeferredChargesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RegulatoryAssetAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RegulatoryAssetAxis=utl_ElectricUtilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RegulatoryAssetAxis=utl_IncomeTaxesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RestructuringCostAndReserveAxis=utl_ContractualObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: