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Income Taxes - Additional Information (Detail) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013
Operating Loss Carryforwards [Line Items] |  |
Alternative Minimum tax credit carryforwards | 2,139,000 us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax | $ 1,538,000 us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax
Internal Revenue Service (IRS) |  |
Operating Loss Carryforwards [Line Items] |  |
NOL carryforward assets expiration date | 2029 |
Federal |  |
Operating Loss Carryforwards [Line Items] |  |
Tax examination description | The Company remains subject to examination by Federal, Maine, Massachusetts, and New Hampshire tax authorities for the tax periods ended December 31, 2011; December 31, 2012; and December 31, 2013. |
Federal and State |  |
Operating Loss Carryforwards [Line Items] |  |
Net Operating Loss carryforward assets | 13,100,000 utl_NetOperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = utl_FederalAndStateMember |
State and Local Jurisdiction |  |
Operating Loss Carryforwards [Line Items] |  |
Net Operating Loss carryforward assets | 1,000,000 utl_NetOperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |
NOL carryforward assets expiration date | 2019 |
Net Operating Loss carryforward assets utilized | 2,700,000 utl_NetOperatingLossCarryforwardsUtilized / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |
Federal Tax |  |
Operating Loss Carryforwards [Line Items] |  |
Net Operating Loss carryforward assets utilized | 3,200,000 utl_NetOperatingLossCarryforwardsUtilized / us-gaap_IncomeTaxAuthorityAxis = utl_FederalTaxMember |
Federal Tax | Internal Revenue Service (IRS) |  |
Operating Loss Carryforwards [Line Items] |  |
Net Operating Loss carryforward assets | 600,000 utl_NetOperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = utl_FederalTaxMember / us-gaap_IncomeTaxAuthorityNameAxis = us-gaap_InternalRevenueServiceIRSMember |

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