XML 88 R69.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Actual Investment Allocations (Detail) | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Pension Plans |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Actual Allocation |  |  | 100.00% | 100.00% | 100.00%
Pension Plans | Equity Funds |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Actual Allocation |  |  | 46.00% | 49.00% | 54.00%
Pension Plans | Fixed Income Securities |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Actual Allocation |  |  | 37.00% | 36.00% | 32.00%
Pension Plans | Equity And Debt Securities |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Actual Allocation | [1] |  | 6.00% | 5.00% | 5.00%
Pension Plans | Other |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Actual Allocation | [2] |  | 0.00% | 0.00% | 8.00%
Other Postretirement Benefit Plans, Defined Benefit |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Actual Allocation |  |  | 100.00% | 100.00% | 100.00%
Other Postretirement Benefit Plans, Defined Benefit | Equity Funds |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Actual Allocation |  |  | 53.00% | 56.00% | 57.00%
Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Actual Allocation |  |  | 47.00% | 44.00% | 43.00%
Scenario Forecast | Pension Plans | Equity Funds |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Target Allocation |  | 47.00% |  |  |
Scenario Forecast | Pension Plans | Fixed Income Securities |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Target Allocation |  | 37.00% |  |  |
Scenario Forecast | Pension Plans | Equity And Debt Securities |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Target Allocation | [1] | 6.00% |  |  |
Scenario Forecast | Pension Plans | Other |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Target Allocation | [2] | 0.00% |  |  |
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Equity Funds |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Target Allocation |  | 55.00% |  |  |
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Target Allocation |  | 45.00% |  |  |
Real Estate Funds | Pension Plans |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Actual Allocation |  |  | 11.00% | 10.00% | 1.00%
Real Estate Funds | Scenario Forecast | Pension Plans |  |  |  |  |
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] |  |  |  |  |
Target Allocation |  | 10.00% |  |  |
[1] | Represents investments in an asset allocation fund. This fund invests in both equity and debt securities.
[2] | Represents investments being held in cash equivalents as of December 31, 2013 pending transfer into a Real Estate Fund.

X
- Definition Target allocation of investments of this type to total plan assets presented on a weighted average basis. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items] + References No definition available. + Details
Name: | utl_ScheduleOfDefinedBenefitPlanAssetAllocationTargetsLineItems
Namespace Prefix: | utl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=utl_EquityAndDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=utl_OtherFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_RealEstateFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |