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Regulatory Matters - Additional Information (Detail) - USD ($)	Jul. 01, 2025	May 01, 2025	Feb. 28, 2025	Dec. 09, 2024	Nov. 26, 2024	Nov. 01, 2024	Oct. 04, 2024	Sep. 11, 2024	Jul. 18, 2024	Jun. 28, 2024	May 01, 2024	Sep. 20, 2023	Aug. 17, 2023	Jul. 26, 2023	Jul. 20, 2022	Jun. 08, 2022	Oct. 31, 2025	Apr. 15, 2025	Oct. 31, 2024	May 31, 2024	May 31, 2023
Regulatory Assets [Line Items]
Requested annual increase in rates											$ 2,100,000
Northern Utilities Inc
Regulatory Assets [Line Items]
Approved annual increase in rates												$ 7,600,000
Return on equity												9.35%
Equity ratio												52.01%
Weighted average cost of capital												7.22%
Northern Utilities Inc | Settlement Agreement [Member]
Regulatory Assets [Line Items]
Approved annual increase in rates															$ 6,100,000
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																$ 1,600,000
Unitil Energy Systems Inc
Regulatory Assets [Line Items]
percent above present rates	3.70%	7.30%
Approved annual increase in rates		$ 18,500,000
Public utilities approved increase amount of annual revenue to recover eligible capital investments	$ 7,800,000
Fitchburg Gas and Electric Light Company
Regulatory Assets [Line Items]
Increase (decrease) in annual revenue						$ 500,000		$ 3,500,000						$ 3,100,000
Percentage of approved return on equity										9.40%
Percentage of approved return on equity, reflecting on equity										52.00%
Percentage of approved return on equity, reflecting on debt										48.00%
Increase in cost										$ 2,200,000
Accumulated deferred income taxes				$ 1,400,000	$ 100,000				$ 1,400,000
Fitchburg Gas and Electric Light Company | July 1, 2024
Regulatory Assets [Line Items]
Approved annual increase in rates										$ 4,700,000			$ 6,800,000
Fitchburg Gas Company
Regulatory Assets [Line Items]
Increase (decrease) in annual revenue													4,200,000
Percentage of approved return on equity										9.40%
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										$ 10,100,000
Increase in cost										$ 4,900,000
Accumulated deferred income taxes				1,400,000					$ 1,400,000
Fitchburg Gas Company | Maximum
Regulatory Assets [Line Items]
Increase (decrease) in annual revenue													$ 6,700,000
Granite State
Regulatory Assets [Line Items]
Increase (decrease) in annual revenue							$ 3,000,000
Fitchburg - Grid Modernization
Regulatory Assets [Line Items]
Regulatory assets approved increase in revenue due to be recovered																		$ 1,400,000		$ 1,300,000	$ 1,000,000
Fitchburg Performance Base Rate Adjustment Electric
Regulatory Assets [Line Items]
Increase (decrease) in annual revenue			$ 1,600,000
Fitchburg Performance Base Rate Adjustment Gas
Regulatory Assets [Line Items]
Increase (decrease) in annual revenue			$ 700,000
Fitchburg Gas System Enhancement Program
Regulatory Assets [Line Items]
Regulatory assets approved increase in revenue due to be recovered																	$ 5,400,000		$ 3,500,000
Gas Division [Member]
Regulatory Assets [Line Items]
Accumulated deferred income taxes				(600,000)
Gas Division [Member] | Fitchburg Gas and Electric Light Company
Regulatory Assets [Line Items]
Accumulated deferred income taxes				(600,000)
Electric Division [Member]
Regulatory Assets [Line Items]
Accumulated deferred income taxes				(800,000)
Electric Division [Member] | Fitchburg Gas and Electric Light Company
Regulatory Assets [Line Items]
Accumulated deferred income taxes				$ (800,000)

X

- Definition

The increase (decrease) during the reporting period in the account that represents the temporary difference that results from Income or Loss that is recognized for accounting purposes but not for tax purposes and vice versa.

+ References

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- Definition

The increase (decrease) during the reporting period in unrecovered fuel costs for a regulated utility company.

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Percentage of public utility's approved debt to capital, including debt and equity.

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Percentage of public utility's requested equity to capital, including debt and equity.

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Amount of public utility's requested rate increase (decrease) with regulatory agency.

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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.

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Public Utility Rate Change Percentage

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Weighted Average Cost Of Capital

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