Joint Plant Ownership (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2025 USD ($) MW	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($) MW	Jun. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Property, plant, and equipment, net		$ 2,238,086		$ 2,238,086		$ 2,149,138
MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Property, plant, and equipment, net		2,238,114		2,238,114		$ 2,149,165
Paris Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[2],[3]	25,000		25,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[2],[3]	$ 23,400		$ 23,400
Paris Units [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)				100.00%
Paris Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[3]	10.00%		10.00%
Paris Units [Member] | Battery storage | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[3]	11		11
Darien Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[2],[4]	$ 63,000		$ 63,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[2],[4]	$ 46,300		$ 46,300
Darien Units [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)				100.00%
Darien Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[4]	10.00%		10.00%
Darien Units [Member] | Solar | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[4]	25		25
Darien Units [Member] | Battery storage | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[4]	7.5		7.5
Koshkonong Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[2],[5]	$ 104,000		$ 104,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[2],[5]	$ 24,800		$ 24,800
Koshkonong Units [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)				100.00%
Koshkonong Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[5]	10.00%		10.00%
Koshkonong Units [Member] | Solar | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[5]	30		30
Koshkonong Units [Member] | Battery storage | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[5]	16.5		16.5
High Noon [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[2],[6]	$ 99,000		$ 99,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[2],[6]	$ 17,800		$ 17,800
High Noon [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)				100.00%
High Noon [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[6]	10.00%		10.00%
High Noon [Member] | Solar | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[6]	30		30
High Noon [Member] | Battery storage | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[6]	16.5		16.5
Columbia Energy Dome [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[2],[7]	$ 17,000		$ 17,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[2],[7]	$ 700		$ 700
Columbia Energy Dome [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)				100.00%
Columbia Energy Dome [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[7]	19.00%		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	[7]	3		3
Paris, Darien, Koshkonong, High Noon, and Columbia Energy Dome Units [Member]
Allowance for Funds Used During Construction
AFUDC		$ 500	$ 1,500	$ 2,100	$ 2,700

[1] 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.

[2] Excluding AFUDC.

[3] Paris Solar-Battery Park is located in the Town of Paris in Kenosha County, Wisconsin.

[4] Darien Solar Energy Center is located in Walworth and Rock Counties in southern Wisconsin.

[5] Koshkonong Solar Energy Center is located in the Towns of Christiana and Deerfield in Dane County, Wisconsin.

[6] High Noon Solar Project is located in Columbia County, Wisconsin.

[7] Columbia Energy Dome is located in Columbia County, Wisconsin.