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Summary of Significant Accounting Policies (Details-2) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Supplemental Cash Flow Information [Abstract] |  |  |  |  |
Interest paid |  | $ 35,755 | $ 34,306 | $ 29,526 |
US Federal | [1] | (3,970) | (16,238) | 4,000 |
Accrued capital expenditures | [2] | 55,283 | 22,734 | 17,247 |
Cash, Cash Equivalents, And Restricted Cash [Abstract] |  |  |  |  |
Cash and cash equivalents |  | 5,666 | 21,302 |  |
Restricted cash |  | 952 | 1,113 |  |
Receivable - margin account |  | 2,118 | 2,081 |  |
Cash, cash equivalents, and restricted cash |  | 8,736 | 24,496 | 15,026 | $ 17,968
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member] |  |  |  |  |
Effects of The Inflation Reduction Act [Abstract] |  |  |  |  |
Guarantor Obligations, Liquidation Proceeds, Monetary Amount |  | 10,900 | 18,500 |  |
Wisconsin |  |  |  |  |
Supplemental Cash Flow Information [Abstract] |  |  |  |  |
US State and Local |  | 10,250 | 3,100 | 5,800 |
US State and Local - Other |  |  |  |  |
Supplemental Cash Flow Information [Abstract] |  |  |  |  |
US State and Local |  | 66 | 36 | 0 |
MGE [Member] |  |  |  |  |
Supplemental Cash Flow Information [Abstract] |  |  |  |  |
Interest paid | [3] | 35,755 | 34,306 | 29,526 |
US Federal | [1] | (5,750) | (18,658) | 3,450 |
Accrued capital expenditures | [2],[3] | 55,283 | 22,734 | 17,247 |
Cash, Cash Equivalents, And Restricted Cash [Abstract] |  |  |  |  |
Cash and cash equivalents |  | 2,248 | 16,865 |  |
Restricted cash |  | 952 | 1,113 |  |
Receivable - margin account |  | 2,118 | 2,081 |  |
Cash, cash equivalents, and restricted cash |  | 5,318 | 20,059 | 6,705 | $ 10,500
MGE [Member] | Wisconsin |  |  |  |  |
Supplemental Cash Flow Information [Abstract] |  |  |  |  |
US State and Local |  | 9,650 | 2,450 | 5,990 |
MGE [Member] | US State and Local - Other |  |  |  |  |
Supplemental Cash Flow Information [Abstract] |  |  |  |  |
US State and Local |  | $ 0 | $ 0 | $ 0 |
[1] | During the years ended December 31, 2025 and December 31, 2024, federal tax payments and receipts included proceeds from the transfer of PTCs under Internal Revenue Code Section 6418. Cash received for income taxes in 2025 includes $10.9 million related to PTCs generated in 2025 that were sold to a third party. Cash received for income taxes in 2024 includes $18.5 million related to PTCs generated in 2024 and 2023 that were sold to a third party.
[2] | Includes a $2.0 million unsecured promissory note, for an acquisition of land, issued to the seller, with all principal and interest paid in January 2026.
[3] | MGE Energy files a consolidated federal income tax return with its subsidiaries. While taxes are filed on a consolidated basis, MGE calculates its respective share of tax liability and makes intercompany tax payments to or from its parent company.

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