XML 48 R33.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Regulatory Liabilities (Detail) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017
--- | --- | --- | ---
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liabilities | $ 60.1 | $ 58.1 | $ 15.0
Less: Current Portion of Regulatory Liabilities | 12.2 | 9.2 | 15.0
Regulatory Liabilities-noncurrent | 47.9 | 48.9 |
Rate Adjustment Mechanisms |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liabilities | 12.2 | 6.9 | 11.6
Gas Pipeline Refund |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liabilities |  | 2.3 | $ 3.4
Income Tax Related Liabilities |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liabilities | $ 47.9 | $ 48.9 |

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

X
- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current 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_RegulatoryLiabilityCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent 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 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_RegulatoryLiabilityNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Details
Name: | us-gaap_RegulatoryLiabilityAxis=utl_GasPipelineRefundMember
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: |