Property, Plant, and Equipment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property, plant, and equipment to be retired	[1]	$ 121,576	$ 133,268
In-service utility plant, net		2,149,138	2,018,121
Construction work in progress		138,208	110,091
Total property, plant, and equipment		2,287,346	2,128,212
Columbia Units [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment to be retired	[2]	121,576	133,268
Impairment of Long-Lived Assets
Impairment of long-lived assets		0
Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		2,702,143	2,506,329
Less: Accumulated depreciation and amortization		789,400	726,289
In-service utility plant, net		1,912,743	1,780,040
Construction work in progress	[3]	134,642	107,724
Electric [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[4]	1,945,748	1,769,559
Gas [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		634,819	603,502
Non Regulated Energy [Member] | Unregulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		326,574	321,951
Less: Accumulated depreciation and amortization		90,179	83,870
In-service utility plant, net		236,395	238,081
Construction work in progress		3,566	2,367
MGE [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment to be retired	[1]	121,576	133,268
In-service utility plant, net		2,149,165	2,018,149
Construction work in progress		138,208	110,091
Total property, plant, and equipment		2,287,373	2,128,240
MGE [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		2,702,170	2,506,357
Less: Accumulated depreciation and amortization		789,400	726,289
In-service utility plant, net		1,912,770	1,780,068
Construction work in progress	[3]	134,642	107,724
MGE [Member] | Electric [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[4]	1,945,764	1,769,576
MGE [Member] | Gas [Member] | Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		634,830	603,513
MGE [Member] | Non Regulated Energy [Member] | Unregulated Operation [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		326,574	321,951
Less: Accumulated depreciation and amortization		90,179	83,870
In-service utility plant, net		236,395	238,081
Construction work in progress		$ 3,566	$ 2,367

[1] 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. In the second quarter of 2021, the operator of Columbia received approval from MISO to retire Columbia Units 1 and 2. The co-owners intend to retire Unit 1 and Unit 2 by the end of 2029. Final timing and retirement dates are subject to change depending on operational, regulatory, capacity needs, and other factors impacting one or more of the Columbia co-owners. As of December 31, 2024, early retirement of Columbia was probable. "Plant anticipated to be retired early" in table above is the net book value of these generating units. Assets for Columbia Unit 1 and Unit 2 are currently included in rate base, and MGE continues to depreciate them on a straight-line basis using the composite depreciation rates approved by the PSCW that included retirement dates of 2029 for Unit 1 and Unit 2. If it becomes probable that regulators will disallow full recovery or a return on the remaining net book value of a generating unit that is either abandoned or probable of being abandoned, an impairment loss would be required. An impairment loss would be recorded to the extent that the remaining net book value of the generating unit exceeds the present value of the amount expected to be recovered from ratepayers. No impairment was recorded as of December 31, 2024.

[2] MGE and the other co-owners announced plans to retire Columbia, a two unit coal-fired generation facility located in Portage, Wisconsin. The co-owners intend to retire Unit 1 and Unit 2 by 2029. Final timing and retirement dates are subject to change depending on operational, regulatory, capacity needs, and other factors impacting one or more of the Columbia co-owners. As of December 31, 2024 and 2023, early retirement of Columbia was probable. See Footnote 4 for further information.

[3] Includes Paris (battery), Darien (solar and battery), and Koshkonong (solar and battery) projects. See Footnote 6 for further information on renewable projects.

[4] Includes Paris Solar placed in service in December 2024. See Footnote 6 for further information on Paris Solar.