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v3.25.2

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands |  | 6 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 31, 2025 USD ($) | Jun. 30, 2025 USD ($) Subsidiary mi | Dec. 31, 2024 USD ($) Megawatts | Jul. 08, 2025 USD ($) | Mar. 31, 2025 USD ($) | Jun. 30, 2024 USD ($)
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Number of Subsidiaries | Entity | Subsidiary |  | 3 |  |  |  |
Length of Pipeline | mi |  | 85 |  |  |  |
Cost of removal obligation |  | $ 147,400 | $ 139,200 |  |  | $ 134,900
Investments in trading securities |  | 6,100 | $ 6,300 |  |  | 5,800
Goodwill |  | 1,600 |  |  |  |
Deductible portion of goodwill |  | $ 400 |  |  |  |
Amortization period |  | 15 years |  |  |  |
Long Term Renewable Contracts |  |  | 30.00% |  |  |
Business Acquisition Liabilities Assumed |  |  |  |  | $ 30,000 |
Energy Storage Systems 1 | Megawatts |  |  | 5,000 |  |  |
Mid Duration Storage | Megawatts |  |  | 1,500 |  |  |
Cash And Cash Equivalents Acquired |  | $ 70,000 |  |  |  |
Asset Acquisition Consideration Transferred |  | 100,000 |  |  |  |
Net Utility Plant |  | 1,644,400 | $ 1,539,600 |  |  | 1,454,800
Allowance for doubtful accounts |  | 1,900 | 2,400 |  |  | 2,200
Regulatory assets |  | 99,200 | 112,000 |  |  | 114,100
Regulatory Liabilities |  | 73,500 | 64,000 |  |  | 57,800
Cash Paid for Acquisition |  | 86,000 |  |  |  |
Loan commitment to fund an acquisition |  | 86,000 |  |  |  |
Electric And Gas Division [Member] |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Business Combination Price Of Acquisition Expected | $ 71,400 |  |  |  |  |
Other Deferred Charges [Member] |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Regulatory assets |  | 14,700 | 14,100 |  |  | 13,100
Unbilled Revenues [member] |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for doubtful accounts |  | 100 | 100 |  |  | 100
Accounts Receivable [member] |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for doubtful accounts |  | $ 1,900 | $ 2,300 |  |  | 2,200
Utilities |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Number of Subsidiaries | Entity | Subsidiary |  | 3 |  |  |  |
Fitchburg Gas And Electric Light Company [Member] |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Energy Storage Systems 1 | Megawatts |  |  | 5,000 |  |  |
Mid Duration Storage | Megawatts |  |  | 1,500 |  |  |
Fitchburg Gas And Electric Light Company [Member] | Other Deferred Charges [Member] | Electric And Gas Division [Member] |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Hardship accounts in regulatory assets |  | $ 8,300 | $ 7,900 |  |  | 7,200
Bangor Natural Gas |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Goodwill |  | 1,600 |  |  |  |
Net Utility Plant |  | 66,700 |  |  |  |
Working Capital |  | 3,800 |  |  |  |
Noncurrent assets |  | 200 |  |  |  |
Regulatory Liabilities |  | 900 |  |  |  |
Subsequent Event [Member] | Bangor Natural Gas |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  | $ 32,000 |  |
Environmental and Rate Case Costs and Other Expenditures | Recovered over the next seven years |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Regulatory assets |  | 7,800 |  |  |  |
ISO-NE Obligations |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Cash Deposits |  | $ 6,000 | 5,000 |  |  | 2,300
Maximum |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Lease term |  | 12 months |  |  |  |
Deferred Compensation Plan [Member] |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Investments in trading securities |  | $ 2,900 | $ 2,200 |  |  | $ 1,900

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