XML 57 R35.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Regulatory Assets Liabilities and Reclassification from Regulatory Assets Liabilities into Cost of Gas Sales (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013
Natural Gas Future/Options Contract |  |  |  |
Regulatory Assets [Line Items] |  |  |  |
Loss/(Gain) recognized in Regulatory Assets(Liabilities) | $ (0.7)utl_DerivativeInstrumentsGainLossRecognizedInRegulatoryAssets / us-gaap_RegulatoryAssetAxis = utl_NaturalGasPurchaseContractMember |  | $ 0.3 utl_DerivativeInstrumentsGainLossRecognizedInRegulatoryAssets / us-gaap_RegulatoryAssetAxis = utl_NaturalGasPurchaseContractMember |
Gas Purchase Costs |  |  |  |
Regulatory Assets [Line Items] |  |  |  |
Loss/(Gain) Reclassified into unaudited Consolidated Statement of Earnings | $ (0.8)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLoss / us-gaap_RegulatoryAssetAxis = utl_GasPurchaseCostsMember | [1] | $ 1.2 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLoss / us-gaap_RegulatoryAssetAxis = utl_GasPurchaseCostsMember | [1]
[1] | These amounts are offset in the Consolidated Statements of Earnings with Accrued Revenue and therefore there is no effect on earnings.

X
- Definition Amount of realized and unrealized loss of derivative instruments not designated or qualifying as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959 + Details
Name: | us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RegulatoryAssetLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Gains and Losses from hedging program recognized in regulatory assets. + References No definition available. + Details
Name: | utl_DerivativeInstrumentsGainLossRecognizedInRegulatoryAssets
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RegulatoryAssetAxis=utl_GasPurchaseCostsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryAssetAxis=utl_NaturalGasPurchaseContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |