XML 43 R28.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2014 Bcf | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 Bcf | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2014 Entity mi Bcf | Dec. 31, 2013 Bcf | Dec. 31, 2012 | Dec. 31, 2015
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of Subsidiaries |  |  |  |  |  |  |  |  | 3 utl_NumberOfSubsidiaries |  |  |
Length Of Pipeline |  |  |  |  |  |  |  |  | 86 utl_LengthOfPipeline |  |  |
Depreciation rate based on average depreciable property balance |  |  |  |  |  |  |  |  | 3.56%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService | 3.59%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService | 3.60%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService |
Common stock dividend paid per share | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid | $ 1.38 us-gaap_CommonStockDividendsPerShareCashPaid | $ 1.38 us-gaap_CommonStockDividendsPerShareCashPaid | $ 1.38 us-gaap_CommonStockDividendsPerShareCashPaid |
Average interest rates |  |  |  |  |  |  |  |  | 1.56%utl_AverageInterestRateOnDebt | 1.92%utl_AverageInterestRateOnDebt | 2.04%utl_AverageInterestRateOnDebt |
Cost of removal obligation | $ 63,800,000 us-gaap_AssetRetirementObligationsNoncurrent |  |  |  | $ 57,300,000 us-gaap_AssetRetirementObligationsNoncurrent |  |  |  | $ 63,800,000 us-gaap_AssetRetirementObligationsNoncurrent | $ 57,300,000 us-gaap_AssetRetirementObligationsNoncurrent |  |
Number of Natural Gas Storage Outstanding | 2.4 utl_NaturalGasAndOilProvedReservesMultiplierToCoverFairValueOfTransactionsOutstanding |  |  |  | 1.8 utl_NaturalGasAndOilProvedReservesMultiplierToCoverFairValueOfTransactionsOutstanding |  |  |  | 2.4 utl_NaturalGasAndOilProvedReservesMultiplierToCoverFairValueOfTransactionsOutstanding | 1.8 utl_NaturalGasAndOilProvedReservesMultiplierToCoverFairValueOfTransactionsOutstanding |  |
Intangible Assets, Purchase Adjustments |  |  |  |  |  |  |  |  | 9,700,000 us-gaap_IndefiniteLivedIntangibleAssetsTranslationAndPurchaseAccountingAdjustments |  |  |
Plant |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Intangible Asset Amortization Period |  |  |  |  |  |  |  |  | 10 years |  |  |
Bargain Purchase Adjustment |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Intangible Asset Amortization Period |  |  |  |  |  |  |  |  | 4 years |  |  |
Maximum |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Cash equivalents maturity period |  |  |  |  |  |  |  |  | 3 months |  |  |
ISO-NE Obligations |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Cash Deposits | 6,300,000 utl_CashDeposits / us-gaap_CashAndCashEquivalentsAxis = utl_NewEnglandMember |  |  |  | 7,300,000 utl_CashDeposits / us-gaap_CashAndCashEquivalentsAxis = utl_NewEnglandMember |  |  |  | 6,300,000 utl_CashDeposits / us-gaap_CashAndCashEquivalentsAxis = utl_NewEnglandMember | 7,300,000 utl_CashDeposits / us-gaap_CashAndCashEquivalentsAxis = utl_NewEnglandMember |  |
Natural Gas Hedging Program |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Cash Deposits | $ 0 utl_CashDeposits / us-gaap_CashAndCashEquivalentsAxis = utl_HedgingObligationsMember |  |  |  | $ 0 utl_CashDeposits / us-gaap_CashAndCashEquivalentsAxis = utl_HedgingObligationsMember |  |  |  | $ 0 utl_CashDeposits / us-gaap_CashAndCashEquivalentsAxis = utl_HedgingObligationsMember | $ 0 utl_CashDeposits / us-gaap_CashAndCashEquivalentsAxis = utl_HedgingObligationsMember |  |
Annual Electric Sales Volume |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of total sales volumes revenue subject to RDM |  |  |  |  |  |  |  |  |  |  |  | 27.00%utl_PercentageOfSalesVolume / us-gaap_ProductOrServiceAxis = utl_ProductTypeOneMember
Annual Natural Gas Sales Volume |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of total sales volumes revenue subject to RDM |  |  |  |  |  |  |  |  |  |  |  | 11.00%utl_PercentageOfSalesVolume / us-gaap_ProductOrServiceAxis = utl_ProductTypeTwoMember
Quarterly Dividends |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Common stock dividend paid per share |  |  |  |  |  |  |  |  | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid / utl_PeriodAxis = utl_QuarterlyPaymentMember | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid / utl_PeriodAxis = utl_QuarterlyPaymentMember | $ 0.345 us-gaap_CommonStockDividendsPerShareCashPaid / utl_PeriodAxis = utl_QuarterlyPaymentMember |
Utilities |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of Subsidiaries |  |  |  |  |  |  |  |  | 3 utl_NumberOfSubsidiaries / dei_LegalEntityAxis = utl_UtilitiesMember |  |  |
Other Subsidiaries |  |  |  |  |  |  |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of Subsidiaries |  |  |  |  |  |  |  |  | 3 utl_NumberOfSubsidiaries / dei_LegalEntityAxis = utl_OtherSubsidiariesMember |  |  |

X
- Definition Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
Name: | us-gaap_AssetRetirementObligationsNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Aggregate dividends paid during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
Name: | us-gaap_CommonStockDividendsPerShareCashPaid
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of increase (decrease) of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit, from foreign currency translation and purchase accounting adjustments. + References No definition available. + Details
Name: | us-gaap_IndefiniteLivedIntangibleAssetsTranslationAndPurchaseAccountingAdjustments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Composite depreciation rate for public utility plants in service. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Average Interest Rate On Debt + References No definition available. + Details
Name: | utl_AverageInterestRateOnDebt
Namespace Prefix: | utl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Cash Deposits + References No definition available. + Details
Name: | utl_CashDeposits
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Cash Equivalents, Maturity Period + References No definition available. + Details
Name: | utl_CashEquivalentsMaturityPeriod
Namespace Prefix: | utl_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Length of natural gas transmission pipeline. + References No definition available. + Details
Name: | utl_LengthOfPipeline
Namespace Prefix: | utl_
Data Type: | num:lengthItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of natural gas purchase contracts outstanding under hedging program. + References No definition available. + Details
Name: | utl_NaturalGasAndOilProvedReservesMultiplierToCoverFairValueOfTransactionsOutstanding
Namespace Prefix: | utl_
Data Type: | num:volumeItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of Subsidiaries. + References No definition available. + Details
Name: | utl_NumberOfSubsidiaries
Namespace Prefix: | utl_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage Of Sales Volume + References No definition available. + Details
Name: | utl_PercentageOfSalesVolume
Namespace Prefix: | utl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | utl_SignificantAccountingPoliciesLineItems
Namespace Prefix: | utl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=utl_OtherSubsidiariesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=utl_UtilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CashAndCashEquivalentsAxis=utl_HedgingObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CashAndCashEquivalentsAxis=utl_NewEnglandMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorPropertyClassAxis=utl_BargainPurchaseAdjustmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorPropertyClassAxis=utl_PlantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ProductOrServiceAxis=utl_ProductTypeOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ProductOrServiceAxis=utl_ProductTypeTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | utl_PeriodAxis=utl_QuarterlyPaymentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |