XML 21 R25.htm IDEA: XBRL DOCUMENT
v3.2.0.727

Summary of Significant Accounting Policies - Additional Information (Detail) | 6 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2015 USD ($) Subsidiary mi Bcf | Dec. 31, 2014 USD ($) Bcf | Jun. 30, 2014 USD ($) Bcf
Significant Accounting Policies [Line Items] |  |  |
Length Of Pipeline | mi | 86 |  |
Cost of Removal Obligations | $ 68,100,000 | $ 63,800,000 | $ 60,800,000
Number of Natural Gas Storage Outstanding | Bcf | 2.9 | 2.4 | 2.3
Maximum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Cash equivalents maturity period | 3 months |  |
ISO-NE Obligations |  |  |
Significant Accounting Policies [Line Items] |  |  |
Cash Deposits | $ 700,000 | $ 6,300,000 | $ 8,800,000
Natural Gas Hedging Program |  |  |
Significant Accounting Policies [Line Items] |  |  |
Cash Deposits | $ 100,000 | $ 0 | $ 0
Utilities |  |  |
Significant Accounting Policies [Line Items] |  |  |
Number of Subsidiaries | Subsidiary | 3 |  |
Other Subsidiaries |  |  |
Significant Accounting Policies [Line Items] |  |  |
Number of Subsidiaries | Subsidiary | 3 |  |

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 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 Significant Accounting Policies [Line Items] + References No definition available. + Details
Name: | utl_SignificantAccountingPoliciesLineItems
Namespace Prefix: | utl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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