Investments (Details-2) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
Jan. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments		$ 9,270	$ 10,221	$ 9,889
Dividends from investment		7,832	8,998	7,347
Capital contributions to investments		4,027	5,601	7,813
MGE Energy [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments		107,883	92,922	87,728
MGE Transco [Member] \| ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments		9,774	10,167	9,889
Dividends from investment		7,832	8,633	7,347
Capital contributions to investments		$ 0	$ 1,249	3,018
Ownership interest in equity-method investee		3.60%	3.60%
MGE Transco [Member] \| ATC [Member] \| Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments	$ 1,200
MGEE Transco [Member] \| ATC Holdco [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments		$ 0	$ 300	$ 100
Ownership interest in equity-method investee		4.40%	4.40%

Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

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