Investment in ATC and ATC Holdco (Details-1) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	$ 2,444	$ 2,266
Dividends from investments	1,967	2,700
Capital contributions to investments	670	1,643
MGE Transco [Member] \| ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	2,420	2,266
Dividends from investments	1,967	2,391
Capital contributions to investments	$ 0	$ 178

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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