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Property, Plant, and Equipment | 12 Months Ended
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Dec. 31, 2025
Property, Plant and Equipment [Abstract] |
Property, Plant and Equipment | Property, Plant, and Equipment - MGE Energy and MGE. Property, plant, and equipment consisted of the following as of December 31:
|  | MGE Energy |  |  | MGE |
(In thousands) |  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Utility: |  |  |  |  |  |  |  |  |  |  |  |
Electric(a)(b) |  | $ | 2,420,281 |  |  | $ | 2,244,796 |  |  | $ | 2,420,298 |  |  | $ | 2,244,812 |
Gas |  |  | 670,271 |  |  |  | 634,819 |  |  |  | 670,282 |  |  |  | 634,830 |
Utility property, plant, and equipment, gross |  |  | 3,090,552 |  |  |  | 2,879,615 |  |  |  | 3,090,580 |  |  |  | 2,879,642 |
Less: Accumulated depreciation and amortization(b) |  |  | 1,047,683 |  |  |  | 966,872 |  |  |  | 1,047,683 |  |  |  | 966,872 |
Utility property, plant, and equipment, net |  |  | 2,042,869 |  |  |  | 1,912,743 |  |  |  | 2,042,897 |  |  |  | 1,912,770 |
Nonregulated: |  |  |  |  |  |  |  |  |  |  |  |
Nonregulated |  |  | 335,005 |  |  |  | 326,574 |  |  |  | 335,005 |  |  |  | 326,574 |
Less: Accumulated depreciation and amortization |  |  | 97,975 |  |  |  | 90,179 |  |  |  | 97,975 |  |  |  | 90,179 |
Nonregulated property, plant, and equipment, net |  |  | 237,030 |  |  |  | 236,395 |  |  |  | 237,030 |  |  |  | 236,395 |
Construction work in progress: |  |  |  |  |  |  |  |  |  |  |  |
Utility construction work in progress(c) |  |  | 288,310 |  |  |  | 134,642 |  |  |  | 288,310 |  |  |  | 134,642 |
Nonregulated construction work in progress |  |  | 4,659 |  |  |  | 3,566 |  |  |  | 4,659 |  |  |  | 3,566 |
Total property, plant, and equipment |  | $ | 2,572,868 |  |  | $ | 2,287,346 |  |  | $ | 2,572,896 |  |  | $ | 2,287,373 |
(a) Includes Paris Battery and Darien Solar placed in service in 2025. See Footnote 6 for further information on Paris and Darien. (b) An asset that will be retired in the near future and substantially in advance of its previously expected retirement date is subject to abandonment accounting. As of December 31, 2024, coal operations at Columbia Units 1 and 2 were expected to conclude by the end of 2029, and therefore met the criteria to be considered probable of abandonment. The related net book value of $121,576 (in thousands) was presented separately in the 2024 Form 10-K. As a minority owner, MGE and the other Columbia co-owners currently plan to continue coal operations at least through 2029. Final timing and retirement dates continue to be evaluated, and depend upon operational regulatory considerations, capacity needs, and availability. As of December 31, 2025, early retirement of Columbia Unit 1 and 2 was no longer probable. (c) Includes Koshkonong (solar and battery), High Noon (solar and battery), Sunnyside (solar and battery), and Saratoga (solar and battery) projects. See Footnote 6 for further information on renewable projects. As of December 31, 2025, MGE's utility plant was subject to a lien with respect to its Indenture of Mortgage and Deed of Trust. In January 2026, MGE completed a redemption of all outstanding first mortgage bonds, and delivered to the Trustee a satisfaction and discharge which, pursuant to the terms of the Indenture, effectively discharged the Indenture. See Footnote 14 for further discussion of the mortgage indenture.

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