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v3.3.1.900

Details on Long Term Debt (Detail) - USD ($) $ in Millions | Mar. 31, 2016 | Dec. 31, 2015 | Mar. 31, 2015
--- | --- | --- | ---
Debt Instrument [Line Items] |  |  |
Total Long-Term Debt | $ 325.3 | $ 325.5 | $ 332.7
Less: Unamortized Debt Issuance Costs | 2.8 | 2.9 | 3.1
Long-Term Debt | 322.5 | 322.6 | 329.6
Less: Current Portion | 17.1 | 17.1 | 3.7
Total Long-term Debt, Less Current Portion | 305.4 | 305.5 | 325.9
6.33% Notes, Due May 1, 2022 |  |  |
Debt Instrument [Line Items] |  |  |
Senior Notes | 20.0 | 20.0 | 20.0
Unitil Energy Systems Inc | First Mortgage Bonds 5.24% Series, Due March 2, 2020 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 15.0 | 15.0 | 15.0
Unitil Energy Systems Inc | First Mortgage Bonds 8.49% Series, Due October 14, 2024 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 12.0 | 12.0 | 15.0
Unitil Energy Systems Inc | First Mortgage Bonds 6.96% Series, Due September 1, 2028 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 20.0 | 20.0 | 20.0
Unitil Energy Systems Inc | First Mortgage Bonds 8.00% Series, Due May 1, 2031 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 15.0 | 15.0 | 15.0
Unitil Energy Systems Inc | First Mortgage Bonds 6.32% Series, Due September 15, 2036 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 15.0 | 15.0 | 15.0
Fitchburg Gas and Electric Light Company | 6.75% Notes, Due November 30, 2023 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 11.4 | 11.4 | 15.2
Fitchburg Gas and Electric Light Company | 7.37% Notes, Due January 15, 2029 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 12.0 | 12.0 | 12.0
Fitchburg Gas and Electric Light Company | 7.98% Notes, Due June 1, 2031 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 14.0 | 14.0 | 14.0
Fitchburg Gas and Electric Light Company | 6.79% Notes, Due October 15, 2025 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 10.0 | 10.0 | 10.0
Fitchburg Gas and Electric Light Company | 5.90% Notes, Due December 15, 2030 |  |  |
Debt Instrument [Line Items] |  |  |
Long-Term Debt | 15.0 | 15.0 | 15.0
Northern Utilities Inc | 6.95% Senior Notes, Series A, Due December 3, 2018 |  |  |
Debt Instrument [Line Items] |  |  |
Senior Notes | 30.0 | 30.0 | 30.0
Northern Utilities Inc | 5.29% Senior Notes, Due March 2, 2020 |  |  |
Debt Instrument [Line Items] |  |  |
Senior Notes | 25.0 | 25.0 | 25.0
Northern Utilities Inc | 7.72% Senior Notes, Series B, Due December 3, 2038 |  |  |
Debt Instrument [Line Items] |  |  |
Senior Notes | 50.0 | 50.0 | 50.0
Northern Utilities Inc | 4.42% Senior Notes, Due October 15, 2044 |  |  |
Debt Instrument [Line Items] |  |  |
Senior Notes | 50.0 | 50.0 | 50.0
Granite State Gas Transmission Inc | 7.15% Senior Notes, Due December 15, 2018 |  |  |
Debt Instrument [Line Items] |  |  |
Senior Notes | 10.0 | 10.0 | 10.0
Unitil Realty Corp | 8.00% Senior Secured Notes, Due August 1, 2017 |  |  |
Debt Instrument [Line Items] |  |  |
Senior Secured Notes | $ 0.9 | $ 1.1 | $ 1.5

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- Definition Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 + Details
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