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Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2017
Income Taxes [Line Items]
Corporate federal income tax		21.00%	21.00%
Regulatory liability, expected flow back to customers					$ 47.1
Regulatory liability, expected pass back to ratepayers				$ 0.7
Net Operating Loss Carryforwards Utilized For Income Taxes					$ 7.7
Deferred tax assets, operating loss carryforwards, federal				$ 3.6
Percentage of employment retention credit		50.00%
Employment retention duties capacity		100.00%
Consolidated Appropriations Act 2021 [Member]
Income Taxes [Line Items]
Percentage of employment retention credit	70.00%
Employment retention duties capacity	100.00%
Minimum
Income Taxes [Line Items]
Average Rate Assumption Method estimated flow back period		15 years
Maximum
Income Taxes [Line Items]
Average Rate Assumption Method estimated flow back period		20 years
Gas Ratepayers | Massachusetts And Maine [Member]
Income Taxes [Line Items]
Regulatory liability, expected flow back to customers		$ 3.6
Tax Year 2018
Income Taxes [Line Items]
Corporate federal income tax		21.00%			21.00%	21.00%

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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