Investment in ATC and ATC Holdco (Details-1) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment			$ 7,440	$ 7,780
Dividends from investments			5,842	6,929
Capital contributions to investments			4,227	4,007
MGE Transco [Member] \| ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	$ 2,500	$ 2,319	7,333	7,724
Dividends from investments	1,942	2,349	5,842	6,620
Capital contributions to investments	$ 0	$ 359	$ 0	$ 892

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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