XML 46 R34.htm IDEA: XBRL DOCUMENT
v3.22.2

Fair Value of Marketable Securities (Detail) - USD ($) $ in Millions | Jun. 30, 2022 | Dec. 31, 2021 | Jun. 30, 2021
--- | --- | --- | ---
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | $ 5.4 | $ 5.7 | $ 5.5
Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 0.8 | 0.6 | 0.7
Fair Value, Inputs, Level 1 |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 5.4 | 5.7 | 5.5
Fair Value, Inputs, Level 1 | Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 0.8 | 0.6 | 0.7
Fair Value, Inputs, Level 1 | Equity Funds | Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 0.4 | 0.2 | 0.3
Fair Value, Inputs, Level 1 | Money Market Funds |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | 5.4 | 5.7 | 5.5
Fair Value, Inputs, Level 1 | Money Market Funds | Deferred Compensation Plan [Member] |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Trading Securities | $ 0.4 | $ 0.4 | $ 0.4

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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (f) -URI https://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(2)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_TradingSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_AwardTypeAxis=utl_DeferredCompensationPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | utl_InvestmentTypesAxis=us-gaap_EquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | utl_InvestmentTypesAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |