Joint Plant Ownership (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2023 USD ($) MW	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) MW	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Property, plant, and equipment, net		$ 1,902,032		$ 1,902,032		$ 1,865,352
MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Property, plant, and equipment, net		1,902,060		1,902,060		$ 1,865,380
Red Barn Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[2]	18,000		18,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[1],[2]	$ 16,500		$ 16,500
Red Barn Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[2]	10.00%		10.00%
Red Barn Units [Member] | Wind | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[2]	9.16		9.16
Badger Hollow II Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[3],[4]	$ 86,000		$ 86,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[1],[4],[5]	$ 58,900		$ 58,900
Badger Hollow II Units [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)				100.00%
Badger Hollow II Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[4]	33.00%		33.00%
Badger Hollow II Units [Member] | Solar | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[4]	50		50
Paris Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[3],[6]	$ 61,000		$ 61,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[1],[6]	$ 34,500		$ 34,500
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	[6]	10.00%		10.00%
Paris Units [Member] | Solar | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[6]	20		20
Paris Units [Member] | Battery storage | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[6]	11		11
Darien Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[3],[7],[8]	$ 46,000		$ 46,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[1],[8]	$ 21,900		$ 21,900
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	[8]	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	[8]	25		25
West Riverside Energy Center [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1]	$ 25,000		$ 25,000
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[1]	$ 24,700		$ 24,700
West Riverside Energy Center [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest		3.40%		3.40%
West Riverside Energy Center [Member] | Natural gas | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW		25		25
Badger Hollow II, Paris, and Darien Units [Member]
Allowance for Funds Used During Construction
AFUDC		$ 1,900	$ 1,100	$ 4,800	$ 2,100

[1] Excluding AFUDC.

[2] The Red Barn Wind Farm is located in the Towns of Wingville and Clifton in Grant County, Wisconsin.

[3] Estimated costs are expected to exceed PSCW previously approved 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.

[4] The Badger Hollow II solar farm is located in southwestern Wisconsin in Iowa County, near the villages of Montfort and Cobb.

[5] Includes an allocation of common facilities at Badger Hollow placed in service in November 2021.

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

[7] As part of its order, the PSCW approved battery capacity with this project, which is no longer included in the current estimate. We will continue to evaluate timing, cost, and feasibility of the installation of batteries.

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