Property, Plant, and Equipment (Details) - USD ($) $ in Thousands		Dec. 31, 2025	Dec. 31, 2024
Property, Plant and Equipment [Line Items]
In-service utility plant, net		$ 2,279,899	$ 2,149,138
Construction work in progress		292,969	138,208
Total property, plant, and equipment		2,572,868	2,287,346
Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		3,090,552	2,879,615
Less: Accumulated depreciation and amortization		1,047,683	966,872
In-service utility plant, net		2,042,869	1,912,743
Construction work in progress	[1]	288,310	134,642
Electric [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[2],[3]	2,420,281	2,244,796
Gas [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		670,271	634,819
Non Regulated Energy [Member] | Unregulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		335,005	326,574
Less: Accumulated depreciation and amortization		97,975	90,179
In-service utility plant, net		237,030	236,395
Construction work in progress		4,659	3,566
MGE [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, net		2,279,927	2,149,165
Construction work in progress		292,969	138,208
Total property, plant, and equipment		2,572,896	2,287,373
MGE [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		3,090,580	2,879,642
Less: Accumulated depreciation and amortization		1,047,683	966,872
In-service utility plant, net		2,042,897	1,912,770
Construction work in progress	[1]	288,310	134,642
MGE [Member] | Electric [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[2],[3]	2,420,298	2,244,812
MGE [Member] | Gas [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		670,282	634,830
MGE [Member] | Non Regulated Energy [Member] | Unregulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		335,005	326,574
Less: Accumulated depreciation and amortization		97,975	90,179
In-service utility plant, net		237,030	236,395
Construction work in progress		$ 4,659	$ 3,566

[1] 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.

[2] 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.

[3] Includes Paris Battery and Darien Solar placed in service in 2025. See Footnote 6 for further information on Paris and Darien.