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Investments (Details-2) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |
Equity earnings of investments | $ 9,889 | $ 8,821 |  | $ 10,125 |
Dividends from investment | 7,347 | 6,958 |  | 8,803 |
Capital contributions to investments | 7,813 | 5,926 |  | 11,081 |
MGE Energy [Member] |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |
Equity earnings of investments | 87,728 | 85,220 |  | 99,246 |
MGE Transco [Member] | ATC [Member] |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |
Equity earnings of investments | 9,889 | 8,821 |  | 10,125 |
Dividends from investment | 7,347 | 4,611 | [1] | 9,078 | [1]
Capital contributions to investments | $ 3,018 | $ 2,841 |  | 3,551 |
Ownership interest in equity-method investee | 3.60% | 3.60% |  |  |
Dividend receivable from ATC |  |  |  | 2,300 |
MGEE Transco [Member] | ATC Holdco [Member] |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |
Capital contributions to investments | $ 100 | $ 300 |  | $ 2,900 |
Ownership interest in equity-method investee | 4.40% | 4.40% |  |  |
[1] | MGE Transco recorded a $2.3 million dividend receivable from ATC as of December 31, 2017. A cash dividend was received in January of 2018.

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