XML 53 R38.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Details on Long Term Debt (Detail) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017
--- | --- | --- | ---
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | $ 396.0 | $ 409.4 | $ 336.2
Less: Unamortized Debt Issuance Costs | 3.1 | 3.3 | 2.8
Long-Term Debt | 392.9 | 406.1 | 333.4
Less: Current Portion | 31.8 | 29.8 | 29.8
Total Long-term Debt, Less Current Portion | 361.1 | 376.3 | 303.6
Long-Term Debt | 392.9 | 406.1 | 333.4
6.33% Senior Notes, Due May 1, 2022 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 20.0 | 20.0 | 20.0
3.70% Senior Notes, Due August 1, 2026 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 30.0 | 30.0 | 30.0
Unitil Energy Systems Inc | First Mortgage Bonds 5.24% Senior Secured Notes, Due March 2, 2020 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 10.0 | 15.0 | 15.0
Unitil Energy Systems Inc | First Mortgage Bonds 8.49% Senior Secured Notes, Due October 14, 2024 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 7.5 | 7.5 | 9.0
Unitil Energy Systems Inc | First Mortgage Bonds 6.96% Senior Secured Notes, Due September 1, 2028 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 20.0 | 20.0 | 20.0
Unitil Energy Systems Inc | First Mortgage Bonds 8.00% Senior Secured Notes, Due May 1, 2031 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 15.0 | 15.0 | 15.0
Unitil Energy Systems Inc | First Mortgage Bonds 6.32% Senior Secured Notes, Due September 15, 2036 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 15.0 | 15.0 | 15.0
Fitchburg Gas and Electric Light Company | 6.75% Senior Notes, Due November 30, 2023 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 7.6 | 7.6 | 9.5
Fitchburg Gas and Electric Light Company | 6.79% Senior Notes, Due October 15, 2025 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 10.0 | 10.0 | 10.0
Fitchburg Gas and Electric Light Company | 3.52% Senior Notes, Due November 1, 2027 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 10.0 | 10.0 |
Fitchburg Gas and Electric Light Company | 7.37% Notes, Due January 15, 2029 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 12.0 | 12.0 | 12.0
Fitchburg Gas and Electric Light Company | 5.90% Notes, Due December 15, 2030 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 15.0 | 15.0 | 15.0
Fitchburg Gas and Electric Light Company | 7.98% Notes, Due June 1, 2031 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 14.0 | 14.0 | 14.0
Fitchburg Gas and Electric Light Company | 4.32% Senior Notes, Due November 1, 2047 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 15.0 | 15.0 |
Northern Utilities Inc | 3.52% Senior Notes, Due November 1, 2027 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 20.0 | 20.0 |
Northern Utilities Inc | 4.32% Senior Notes, Due November 1, 2047 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 30.0 | 30.0 |
Northern Utilities Inc | 6.95% Senior Notes, Due December 3, 2018 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 10.0 | 10.0 | 20.0
Northern Utilities Inc | 5.29% Senior Notes, Due March 2, 2020 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 16.6 | 25.0 | 25.0
Northern Utilities Inc | 7.72% Senior Notes, Due December 3, 2038 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 50.0 | 50.0 | 50.0
Northern Utilities Inc | 4.42% Senior Notes, Due October 15, 2044 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 50.0 | 50.0 | 50.0
Granite State Gas Transmission Inc | 7.15% Senior Notes, Due December 15, 2018 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | 3.3 | 3.3 | $ 6.7
Granite State Gas Transmission Inc | 3.72% Senior Notes, Due November 1, 2027 |  |  |
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | $ 15.0 | $ 15.0 |

X
- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_LongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19,20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_LongTermDebtCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_LongTermDebtNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_UnamortizedDebtIssuanceExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesSixPointThreeThreePercentDueMayOneTwentyTwentyTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorUnsecuredNotesThreePointSevenZeroPercentDueAugustOneTwentyTwentySixMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_FirstMortgageBondsFivePointTwoFourPercentSeniorSecuredNotesDueMarchTwoTwentyTwentyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_FirstMortgageBondsEightPointFourNinePercentSeniorSecuredNotesDueOctoberFourteenTwentyTwentyFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_FirstMortgageBondsSixPointNineSixPercentSeniorSecuredNotesDueSeptemberOneTwentyTwentyEightMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_FirstMortgageBondsEightPointZeroZeroPercentSeniorSecuredNotesDueMayOneTwentyThirtyOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_FirstMortgageBondsSixPointThreeTwoPercentSeniorSecuredNotesDueSeptemberFifteenTwentyThirtySixMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesSixPointSevenFivePercentDueNovemberThirtyTwentyTwentyThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesSixPointSevenNinePercentDueOctoberFifteenTwentyTwentyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesThreePointFiveTwoPercentDueNovemberOneTwentyTwentySevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesSevenPointThreeSevenPercentDueJanuaryFifteenTwentyTwentyNineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesFivePointNineZeroPercentDueDecemberFifteenTwentyThirtyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesSevenPointNineEightPercentDueJuneOneTwentyThirtyOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesFourPointThreeTwoPercentDueNovemberOneTwentyFortySevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesSixPointNineFivePercentDueDecemberThreeTwentyEighteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesFivePointTwoNinePercentDueMarchTwoTwentyTwentyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesSevenPointSevenTwoPercentDueDecemberThreeTwentyThirtyEightMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesFourPointFourTwoPercentDueOctoberFifteenTwentyFortyFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesSevenPointOneFivePercentDueDecemberFifteenTwentyEighteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=utl_SeniorNotesThreePointSevenTwoPercentDueNovemberOneTwentyTwentySevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |