Property, Plant, and Equipment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Plant anticipated to be retired early		$ 158,983	[1]	$ 0
In-service utility plant, net		1,828,171		1,630,286
Construction work in progress		50,603		139,099
Total property, plant, and equipment		1,878,774		1,769,385
Columbia Units [Member]
Property, Plant and Equipment [Line Items]
Plant anticipated to be retired early	[2]	158,983
Impairment of Long-Lived Assets
Impairment of long-lived assets		0
First Mortgage Bonds [Member] | 7.70%, 2028 Series [Member]
Plant related debt items
Long-term debt, gross	[3]	1,200		1,200
Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		2,221,906		2,105,108
Less: Accumulated depreciation and amortization	[1]	636,804		721,382
In-service utility plant, net		1,585,102		1,383,726
Construction work in progress	[4]	49,211		137,725
Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[1],[4]	1,516,533		1,608,658
Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		546,390		496,450
Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		317,881		320,691
Less: Accumulated depreciation and amortization		74,812		74,131
In-service utility plant, net		243,069		246,560
Construction work in progress		1,392		1,374
MGE [Member]
Property, Plant and Equipment [Line Items]
Plant anticipated to be retired early		158,983	[1]	0
In-service utility plant, net		1,828,199		1,630,314
Construction work in progress		50,603		139,099
Total property, plant, and equipment		1,878,802		1,769,413
MGE [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		2,221,934		2,105,136
Less: Accumulated depreciation and amortization	[1]	636,804		721,382
In-service utility plant, net		1,585,130		1,383,754
Construction work in progress	[4]	49,211		137,725
MGE [Member] | Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[1],[4]	1,516,550		1,608,675
MGE [Member] | Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		546,401		496,461
MGE [Member] | Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		317,881		320,691
Less: Accumulated depreciation and amortization		74,812		74,131
In-service utility plant, net		243,069		246,560
Construction work in progress		$ 1,392		$ 1,374

[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 by the end of 2023 and Unit 2 by the end of 2024. Final timing and retirement dates are subject to change depending on operational, regulatory, and other factors. As of December 31, 2021, 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 2038 for 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 for the difference of the remaining net book value of the generating unit that is greater than the present value of the amount expected to be recovered from ratepayers. No impairment was recorded as of December 31, 2021.

[2] In February 2021, 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 by the end of 2023 and Unit 2 by the end of 2024. Final timing and retirement dates are subject to change depending on operational, regulatory, and other factors. As of December 31, 2021, early retirement of Columbia was probable. See Footnote 4 for further information.

[3] MGE's utility plant is subject to the lien of its Indenture of Mortgage and Deed of Trust, under which its first mortgage bonds are issued. The Mortgage Indenture provides that dividends or any other distribution or purchase of MGE shares may not be made if the aggregate amount thereof since December 31, 1945, would exceed the earned surplus (retained earnings) accumulated subsequent to December 31, 1945. As of December 31, 2021, approximately $604.3 million was available for the payment of dividends under this covenant.

[4] Three major projects were placed in service in 2021. Electric only utility projects were O'Brien Solar Fields completed in May and Badger Hollow I completed in November. Implementation of a new Customer Information System, an electric and gas utility project, went live in September.