v3.26.1
Joint Plant Ownership (Details)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
USD ($)
MW
Mar. 31, 2025
USD ($)
Dec. 31, 2025
USD ($)
Jointly Owned Utility Plant Interests [Line Items]      
Property, plant, and equipment, net $ 2,282,117   $ 2,279,899
Allowance for Funds Used During Construction      
AFUDC $ 3,100 $ 1,600  
Public Service Commission of Wisconsin [Member]      
Allowance for Funds Used During Construction      
Authorized AFUDC rate - Signficiant projects (100%) 100.00%    
MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Property, plant, and equipment, net $ 2,282,145   $ 2,279,927
Darien Units [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [1],[2],[3],[4] 18,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [1],[3],[4] $ 7,400    
Darien Units [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [1],[4] 10.00%    
Darien Units [Member] | Battery storage | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [1],[4] 7.5    
Koshkonong Units [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [2],[3],[4],[5] $ 93,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[4],[5] $ 65,900    
Koshkonong Units [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [4],[5] 10.00%    
Koshkonong Units [Member] | Solar | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[5] 30    
Koshkonong Units [Member] | Battery storage | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[5] 16.5    
High Noon [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [3],[4],[6] $ 99,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[4],[6] $ 60,100    
High Noon [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [4],[6] 10.00%    
High Noon [Member] | Solar | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[6] 30    
High Noon [Member] | Battery storage | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[6] 16.5    
Columbia Energy Dome [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [2],[3],[4],[6] $ 22,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[4],[6] $ 2,000    
Columbia Energy Dome [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [4],[6] 19.00%    
Columbia Energy Dome [Member] | Storage | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[6] 3    
Badger Hollow [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [3],[4],[7] $ 36,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[4],[7] $ 5,600    
Badger Hollow [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [4],[7] 10.00%    
Badger Hollow [Member] | Wind | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[7] 11.2    
Whitetail [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [3],[8] $ 23,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[8] $ 1,200    
Whitetail [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [8] 10.00%    
Whitetail [Member] | Wind | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [8] 6.7    
Dawn Harvest [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [4],[9] $ 34,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[4],[9] $ 1,400    
Dawn Harvest [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [4],[9] 10.00%    
Dawn Harvest [Member] | Solar | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[9] 15    
Ursa [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [2],[3],[4],[6] $ 46,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[4],[6] $ 6,500    
Ursa [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [4],[6] 10.00%    
Ursa [Member] | Solar | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[6] 20    
Saratoga [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [3],[4],[10] $ 46,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[4],[10] $ 11,900    
Saratoga [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [4],[10] 10.00%    
Saratoga [Member] | Solar | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[10] 15    
Saratoga [Member] | Battery storage | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[10] 5    
Good Oak [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [4],[6] $ 22,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[6] $ 1,700    
Good Oak [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [4],[6] 10.00%    
Good Oak [Member] | Solar | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[6] 9.8    
Gristmill [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Projected renewable project costs [4],[6] $ 15,000    
Public Utilities, Property, Plant and Equipment, Construction Work in Progress [3],[6] $ 1,600    
Gristmill [Member] | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, ownership interest [4],[6] 10.00%    
Gristmill [Member] | Solar | MGE [Member]      
Jointly Owned Utility Plant Interests [Line Items]      
Jointly owned utility plant, plant capacity (in MW) | MW [4],[6] 6.7    
[1] Darien Solar Energy Center is located in Walworth and Rock Counties in southern Wisconsin.
[2] 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.
[3] Excluding AFUDC.
[4] MGE received specific approval to recover 100% AFUDC. During the three months ended March 31, 2026, MGE recognized $3.1 million, after tax, in AFUDC for these projects compared to $1.6 million for the comparable period in 2025.
[5] Koshkonong Solar Energy Center is located in the Towns of Christiana and Deerfield in Dane County, Wisconsin.
[6] Located in Columbia County, Wisconsin.
[7] Badger Hollow Wind is located in Iowa and Grant Counties, Wisconsin.
[8] Whitetail Wind is located in Grant County, Wisconsin.
[9] Dawn Harvest Solar Energy Center is located in Rock County, Wisconsin.
[10] Saratoga Solar Energy Center is located in Wood County, Wisconsin.