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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

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