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Regulatory Matters - Additional Information (Detail) - USD ($) $ in Millions | May 01, 2024 | Nov. 27, 2023 | Nov. 01, 2023 | Sep. 20, 2023 | Aug. 17, 2023 | Jul. 27, 2023 | Jul. 26, 2023 | May 31, 2023 | Aug. 19, 2022 | Jul. 28, 2022 | Jul. 20, 2022 | Jun. 08, 2022 | May 12, 2022 | May 03, 2022 | Aug. 24, 2021 | Nov. 30, 2020 | Apr. 15, 2024 | Oct. 31, 2023 | Oct. 31, 2022
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Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested annual increase in rates | $ 2.4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Northern Utilities Inc |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of approved return on equity |  |  |  |  |  |  |  |  |  |  |  |  | 9.20% |  |  |  |  |  |
Percentage of approved return on equity, reflecting on equity |  |  |  |  |  |  |  |  |  |  |  |  | 52.00% |  |  |  |  |  |
Percentage of approved return on equity, reflecting on debt |  |  |  |  |  |  |  |  |  |  |  |  | 48.00% |  |  |  |  |  |
Approved annual increase in rates |  |  |  | $ 7.6 |  |  |  |  |  |  |  |  |  | $ 6.3 |  |  |  |  |
Return on equity |  |  |  | 9.35% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity ratio |  |  |  | 52.01% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average cost of capital |  |  |  | 7.22% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities approved increase amount of annual revenue to recover eligible capital investments |  |  |  |  |  |  |  | $ 1.2 |  | $ 1.3 |  |  |  |  |  |  |  |  |
Northern Utilities Inc | Settlement Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved annual increase in rates |  |  |  |  |  |  |  |  |  |  | $ 6.1 |  |  |  |  |  |  |  |
Northern Utilities Inc | Arrearage Management Program [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expenses associated with the program excluded from the revenue requirement as per order and adjusted increase amount will result in reasonable rates |  |  |  |  |  |  |  |  |  |  |  |  | $ 5.9 |  |  |  |  |  |
Northern Utilities Inc | New Hampshire |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of approved return on equity |  |  |  |  |  |  |  |  |  |  | 9.30% |  |  |  |  |  |  |  |
Percentage of approved return on equity, reflecting on equity |  |  |  |  |  |  |  |  |  |  | 52.00% |  |  |  |  |  |  |  |
Percentage of approved return on equity, reflecting on debt |  |  |  |  |  |  |  |  |  |  | 48.00% |  |  |  |  |  |  |  |
Requested annual increase in rates |  |  |  |  |  |  |  |  |  |  |  | $ 1.6 |  |  |  |  |  |  |
Fitchburg Gas and Electric Light Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual revenue |  | $ 3.5 | $ 3.6 |  |  |  | $ 3.1 |  |  |  |  |  |  |  |  |  |  |  |
Transfer revenue amount |  |  |  |  | $ 2.7 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved annual increase in rates |  |  |  |  | 4.1 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fitchburg Gas and Electric Light Company | July 1, 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved annual increase in rates |  |  |  |  | 6.8 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fitchburg Gas Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual revenue |  |  |  |  | 4.2 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets approved increase in revenue due to be recovered |  |  |  |  | $ 6.7 |  |  |  |  |  |  |  |  |  |  |  |  | $ 6.4 | $ 4.5
Granite State |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual revenue |  |  |  |  |  | $ 1.0 |  |  | $ 0.3 |  |  |  |  |  | $ 0.1 | $ 1.3 |  |  |
Fitchburg - Grid Modernization |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets approved increase in revenue due to be recovered |  |  |  |  |  |  |  | $ 1.0 |  |  |  |  |  |  |  |  | $ 1.3 |  |

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- Definition The increase (decrease) during the reporting period in unrecovered fuel costs for a regulated utility company. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (a) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-28 + Details
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- 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
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- Definition Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481878/980-340-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 55 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481849/980-340-55-2 + Details
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- Definition Expenses associated with the program excluded from the revenue requirement as per order and adjusted increase amount will result in reasonable rates + References No definition available. + Details
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