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Regulatory Matters - Additional Information (Detail)																1 Months Ended	3 Months Ended	6 Months Ended
	Jul. 28, 2022 USD ($)	Jul. 20, 2022 USD ($)	Jul. 15, 2022 USD ($)	Jun. 30, 2022 USD ($)	Jun. 08, 2022 USD ($)	May 12, 2022 USD ($)	May 03, 2022 USD ($)	May 01, 2022 USD ($)	Jan. 31, 2022 USD ($)	Aug. 24, 2021 USD ($)	Mar. 01, 2021 USD ($)	Nov. 30, 2020 USD ($)	Mar. 26, 2020 USD ($)	Feb. 28, 2020 USD ($)	Jul. 01, 2018 MW	Mar. 31, 2020 USD ($)	Mar. 31, 2022 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2027 MW	Dec. 31, 2022 MW	May 27, 2022 USD ($)	May 01, 2021 USD ($)	Mar. 10, 2021 MW	May 31, 2019 MW	Aug. 09, 2018 MW	Jul. 31, 2018 Bcf MW	Jun. 30, 2017 MW
Regulatory Assets [Line Items]
Approved annual increase in rates													$ 3,600,000			$ 4,600,000
Increase in annual base rate													3.60%
Requested annual increase in rates								$ 1,500,000
Approved annual increase in rates																$ 3,700,000
Approved Recover Amount In COVID Nineteen Related Costs Relating To Expenses As Per Authorization Provided In Order				$ 386,957
Second Solicitation [Member]
Regulatory Assets [Line Items]
Power generation capacity | MW															800
Second Rate Step Adjustments
Regulatory Assets [Line Items]
Power generation capacity | MW															800
Other Restructuring
Regulatory Assets [Line Items]
Cost recovery period, years																		2 years
Offshore Wind Energy
Regulatory Assets [Line Items]
Power generation facility | MW																			1,600
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							$ 6,300,000
Public utilities approved increase amount of annual revenue to recover eligible capital investments	$ 1,300,000
Approved Recover Amount In COVID Nineteen Related Costs Relating To Expenses As Per Authorization Provided In Order				68,061
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						$ 5,900,000
Northern Utilities Inc | ME
Regulatory Assets [Line Items]
Percentage of approved return on equity													9.48%
Percentage of approved return on equity, reflecting on equity													50.00%
Percentage of approved return on equity, reflecting on debt													50.00%
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
Threshold amount that will be allowed to adjust distribution rates upward or downward during the term of stay out period			$ 200,000
Northern Utilities Inc | New Hampshire | Settlement Agreement [Member]
Regulatory Assets [Line Items]
Approved annual increase in rates		$ 6,100,000
Fitchburg Gas and Electric Light Company
Regulatory Assets [Line Items]
Percentage of approved return on equity									9.70%
Percentage of approved return on equity, reflecting on equity									52.45%
Percentage of approved return on equity, reflecting on debt									47.55%
Revenue impact threshold									$ 100,000
Fitchburg Gas and Electric Light Company | Offshore Wind Energy
Regulatory Assets [Line Items]
Power generation facility | Bcf																										400
Remuneration Percentage																										2.75%	2.75%
Fitchburg Gas and Electric Light Company | Offshore Wind Energy | First Solicitation [Member]
Regulatory Assets [Line Items]
Power generation facility | MW																									1,600
Fitchburg Gas and Electric Light Company | Offshore Wind Energy | Second Solicitation [Member]
Regulatory Assets [Line Items]
Power generation facility | MW																							1,600	1,600
Fitchburg Gas and Electric Light Company | Qualified Clean Energy
Regulatory Assets [Line Items]
Power generation capacity | MW																										9,554,940
Fitchburg Gas and Electric Light Company | Minimum [Member] | Offshore Wind Energy
Regulatory Assets [Line Items]
Power generation facility | MW																											400
Fitchburg Gas and Electric Light Company | Scenario Forecast
Regulatory Assets [Line Items]
Power generation capacity | MW																				9,450,000
Fitchburg Gas Company
Regulatory Assets [Line Items]
Percentage of approved return on equity														9.70%
Percentage of approved return on equity, reflecting on equity														52.45%
Percentage of approved return on equity, reflecting on debt														47.55%
Regulatory assets approved increase in revenue due to be recovered																					$ 400,000	$ 2,200,000
Approved annual increase in rates									$ 1,100,000		$ 900,000
Approved annual increase in rates																	$ 900,000
Apporved annual decrease in rates																	$ 200,000
Revenue impact threshold														$ 40,000
Granite State
Regulatory Assets [Line Items]
Increase (decrease) in annual revenue	$ 300,000									$ 100,000		$ 1,300,000
Spending cap				$ 14,600,000														$ 14,600,000

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