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Property, Plant, and Equipment (Tables) | 12 Months Ended
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Dec. 31, 2025
Property, Plant and Equipment [Abstract] |
Schedule of Property, Plant, and Equipment | 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.

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- Definition Tabular disclosure of physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, balances by class of assets, depreciation and depletion expense and method used, including composite depreciation, and accumulated deprecation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -SubTopic 10 -Topic 360 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482099/360-10-50-1 + Details
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