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v2.4.1.9

Summary of Changes in the Fair Value of the Pension Plan Level 3 Assets (Detail) (SEI Core Property Collective Investment Trust Fund, USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Actual Return on Investments: |  |  |  |
Plan Assets at End of Year | $ 8,172,378 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets | [1] | $ 1,125,000 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets | [1]
Fair Value, Inputs, Level 3 |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Plan Assets at Beginning of Year | 1,125,000 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = utl_SeiCorePropertyCollectiveInvestmentTrustFundMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  |  |
Actual Return on Investments: |  |  |  |
Related to Investments Held at Year-End | 672,378 us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = utl_SeiCorePropertyCollectiveInvestmentTrustFundMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  |  |
Related to Investments Sold During the Year | 0 us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = utl_SeiCorePropertyCollectiveInvestmentTrustFundMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 0 us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = utl_SeiCorePropertyCollectiveInvestmentTrustFundMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Total Return on Investments | 672,378 us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = utl_SeiCorePropertyCollectiveInvestmentTrustFundMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  |  |
Purchases, Sales and Settlements | 6,375,000 us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = utl_SeiCorePropertyCollectiveInvestmentTrustFundMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 1,125,000 us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = utl_SeiCorePropertyCollectiveInvestmentTrustFundMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Plan Assets at End of Year | $ 8,172,378 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = utl_SeiCorePropertyCollectiveInvestmentTrustFundMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | $ 1,125,000 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = utl_SeiCorePropertyCollectiveInvestmentTrustFundMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
[1] | The SEI Core Property Collective Investment Trust Fund, through the SEI Core Property Fund, seeks both current income and long-term capital appreciation through investing in underlying funds that acquire, manage, and dispose of commercial real estate properties.

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- Definition The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost) -URI http://asc.fasb.org/extlink&oid=6504192 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Actual Return on Plan Assets (Component of Net Periodic Pension Cost) -URI http://asc.fasb.org/extlink&oid=6504226 + Details
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- Definition Actual return on plan assets, separately identifying the amount related to assets sold during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920 + Details
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- Definition Actual return on plan assets, separately identifying the amount related to assets still held at the reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920 + Details
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- Definition Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=29635418&loc=d3e12355-114930 + Details
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- Definition Amount of increase (decrease) in plan assets from purchases, sales and settlement of plan obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(B) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(iv)(02)(B) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920 + Details
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