Investment in ATC and ATC Holdco (Details-1) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 2019
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC		$ 2,266	$ 2,218
Dividends from ATC		2,700	2,012
Capital contributions to investments		1,643	740
MGE Transco [Member] \| ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC		2,266	2,218
Dividends from ATC		2,391	2,012
Capital contributions to investments		$ 178	$ 178
MGE Transco [Member] \| ATC [Member] \| Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments	$ 400

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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