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
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