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Joint Plant Ownership (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2025
USD ($)
MW
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Columbia Units [Member]      
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [1] $ 301,705 $ 299,048  
Accumulated depreciation [1] (202,111) (177,472)  
Construction work in progress [1] $ 4,665 1,724  
Columbia Units [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [1] 211    
Jointly owned utility plant, ownership interest [1] 19.00%    
Jointly owned utility plant, fuel, operating, and maintenance expense [1] $ 37,684 29,815 $ 30,103
Elm Road Units [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, fuel, operating, and maintenance expense [2] $ 23,809 21,511 21,072
Elm Road Units [Member] | MGE Power Elm Road [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [2] 106    
Jointly owned utility plant, ownership interest [2] 8.33%    
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [2] $ 209,502 207,070  
Accumulated depreciation [2] (51,850) (47,494)  
Construction work in progress [2] 485 514  
West Campus [Member] | UW [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, fuel, operating, and maintenance expense [3] $ 8,400 7,000 6,700
West Campus [Member] | MGE Power West Campus [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4] 157    
Jointly owned utility plant, ownership interest [4] 55.00%    
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [4] $ 124,316 118,317  
Accumulated depreciation [4] (45,346) (41,939)  
Construction work in progress [4] 4,174 3,052  
West Riverside Energy Center [Member]      
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [5] 56,394 54,996  
Accumulated depreciation [5] (9,331) (7,421)  
Construction work in progress [5] $ 342 404  
West Riverside Energy Center [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [5] 50    
Jointly owned utility plant, ownership interest [5] 6.90%    
Jointly owned utility plant, fuel, operating, and maintenance expense [5] $ 1,826 5,954 3,214
Forward Wind [Member]      
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [6] 34,348 34,363  
Accumulated depreciation [6] (19,123) (18,069)  
Construction work in progress [6] $ 3,954 0  
Forward Wind [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [6] 18    
Jointly owned utility plant, ownership interest [6] 12.80%    
Jointly owned utility plant, fuel, operating, and maintenance expense [6] $ 596 755 677
Two Creeks [Member]      
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [7] 68,003 67,999  
Accumulated depreciation [7] (12,357) (9,951)  
Construction work in progress [7] $ 37 0  
Two Creeks [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [7] 50    
Jointly owned utility plant, ownership interest [7] 33.00%    
Jointly owned utility plant, fuel, operating, and maintenance expense [7] $ 1,137 961 1,087
Badger Hollow I and II [Member]      
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [8] 161,432 160,954  
Accumulated depreciation [8] (16,276) (10,639)  
Construction work in progress [8] $ 0 368  
Badger Hollow I and II [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [8] 100    
Jointly owned utility plant, ownership interest [8] 33.00%    
Jointly owned utility plant, fuel, operating, and maintenance expense [8] $ 1,804 1,494 751
Red Barn Units [Member]      
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [9] 16,750 16,484  
Accumulated depreciation [9] (1,391) (872)  
Construction work in progress [9] $ 22 0  
Red Barn Units [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [9] 9.16    
Jointly owned utility plant, ownership interest [9] 10.00%    
Jointly owned utility plant, fuel, operating, and maintenance expense [9] $ 209 213 $ 143
Paris Units [Member]      
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [10] 27,549 40,565  
Accumulated depreciation [10] (586) 0  
Construction work in progress [10] $ 0 0  
Paris Units [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [10] 10.00%    
Jointly owned utility plant, fuel, operating, and maintenance expense [10] $ 441 $ 23  
Paris Units [Member] | MGE [Member] | Solar Generation Source [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [10] 20    
Paris Units [Member] | MGE [Member] | Battery Storage For Renewable Energy [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [10] 11    
Darien Units [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected Renewable Project Costs [11],[12],[13] $ 18,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [11] 7,400    
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]      
Plant [14] 1,998    
Accumulated depreciation [14] (44)    
Construction work in progress [14] $ 0    
Darien Units [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [11],[14] 10.00%    
Jointly owned utility plant, fuel, operating, and maintenance expense [14] $ 295    
Darien Units [Member] | MGE [Member] | Solar Generation Source [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [14] 25    
Darien Units [Member] | MGE [Member] | Battery Storage For Renewable Energy [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [11] 7.5    
Koshkonong Units [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected Renewable Project Costs [12],[13],[15] $ 93,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [15] $ 64,700    
Koshkonong Units [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [15] 10.00%    
Koshkonong Units [Member] | MGE [Member] | Solar Generation Source [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [15] 30    
Koshkonong Units [Member] | MGE [Member] | Battery Storage For Renewable Energy [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [15] 16.5    
High Noon [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected Renewable Project Costs [13],[16] $ 99,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [16] $ 59,500    
High Noon [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [16] 10.00%    
High Noon [Member] | MGE [Member] | Solar Generation Source [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [16] 30    
High Noon [Member] | MGE [Member] | Battery Storage For Renewable Energy [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [16] 16.5    
Columbia Energy Dome [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected Renewable Project Costs [13],[17] $ 22,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [17] $ 2,700    
Columbia Energy Dome [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [17] 19.00%    
Columbia Energy Dome [Member] | MGE [Member] | Storage for Renewable Energy [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [17] 3    
Badger Hollow [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected Renewable Project Costs [13],[18] $ 36,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [18] $ 5,600    
Badger Hollow [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [18] 10.00%    
Badger Hollow [Member] | MGE [Member] | Wind Generation Source [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [18] 11.2    
Whitetail [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected Renewable Project Costs [13],[19] $ 23,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [19] $ 1,200    
Whitetail [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [19] 10.00%    
Whitetail [Member] | MGE [Member] | Wind Generation Source [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [19] 6.7    
Ursa [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected Renewable Project Costs [13],[20] $ 46,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [20] $ 6,400    
Ursa [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [20] 10.00%    
Ursa [Member] | MGE [Member] | Solar Generation Source [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [20] 20    
Saratoga [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected Renewable Project Costs [13],[21] $ 46,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [21] $ 10,200    
Saratoga [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [21] 10.00%    
Saratoga [Member] | MGE [Member] | Solar Generation Source [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [21] 15    
Saratoga [Member] | MGE [Member] | Battery Storage For Renewable Energy [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [21] 5    
[1] As of December 31, 2024, coal operations were expected to conclude at Columbia Units 1 and 2 by the end of 2029, and thus at that time Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. 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. See Footnote 4 for further information.
[2] Two coal-fired generating units in Oak Creek, Wisconsin. In October 2025, MGE, along with the plant co-owners, filed a joint application with the PSCW to end the use of coal as a primary fuel at the Elm Road Units and transition the plant to natural gas. By the end of 2030, coal is expected to be used only as a backup fuel at the Elm Road Units. By the end of 2032, MGE expects that the Elm Road Units will be fully transitioned away from coal.
[3] Operating charges are allocated to the UW based on formulas contained in the operating agreement. Under the provisions of this arrangement, the UW is required to reimburse MGE for their allocated portion of fuel and operating expenses. For the years ended December 31, 2025, 2024, and 2023, the UW's allocated share of fuel and operating costs was $8.4 million, $7.0 million, and $6.7 million, respectively.
[4] MGE Power West Campus and the UW jointly own the West Campus Cogeneration Facility (WCCF) located on the UW campus in Madison, Wisconsin. The UW owns a controlling interest in the chilled-water and steam plants, which are used to meet the needs for air-conditioning and steam-heat capacity for the UW campus. MGE Power West Campus owns a controlling interest in the electric generation plant, which is leased and operated by MGE.
[5] In March 2023, MGE purchased an ownership interest in West Riverside, a natural gas-fired facility located in Beloit, WI, from WPL, operator and co-owner of the plant. West Riverside was placed in-service in 2020. In June 2024, MGE purchased an additional ownership interest in West Riverside, increasing its interest to 6.9%.
[6] The Forward Wind Energy Center (Forward Wind) consists of 86 wind turbines located near Brownsville, Wisconsin.
[7] The Two Creeks solar generation array is located in the Town of Two Creeks and the City of Two Rivers in Manitowoc and Kewaunee Counties, Wisconsin. Date of commercial operation of the solar array was November 2020.
[8] The Badger Hollow I and II solar farm is located in southwestern Wisconsin in Iowa County, near the villages of Montfort and Cobb. Date of commercial operation of Badger Hollow I was November 2021 and December 2023 for Badger Hollow II.
[9] The Red Barn Wind Farm is located in the Towns of Wingville and Clifton in Grant County, Wisconsin. MGE purchased its share of Red Barn in 2023.
[10] The Paris Solar-Battery Park is located in the Town of Paris in Kenosha County, Wisconsin. Date of commercial operation of the solar array was December 2024. Date of commercial operation of battery was June 2025.
[11] Darien Solar Energy Center is located in Walworth and Rock Counties in southern Wisconsin.
[12] Estimated costs are expected to exceed PSCW previously approved Certificate of Authority (CA) levels. Notifications are provided to the PSCW when costs increase above CA levels. MGE has and will continue to request recovery of the updates in its rate case proceedings.
[13] Excluding AFUDC.
[14] The Darien Solar Energy Center is located in Walworth and Rock Counties in southern Wisconsin. Date of commercial operation of the solar array was March 2025.
[15] Koshkonong Solar Energy Center is located in the Towns of Christiana and Deerfield in Dane County, Wisconsin.
[16] High Noon Solar Project is located in Columbia County, Wisconsin.
[17] Columbia Energy Dome is located in Columbia County, Wisconsin.
[18] Badger Hollow Wind is located in Iowa and Grant Counties, Wisconsin.
[19] Whitetail Wind is located in Grant County, Wisconsin.
[20] Ursa Solar Park is located in Columbia County, Wisconsin.
[21] Saratoga Solar Energy Center is located in Wood County, Wisconsin.