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v3.19.3.a.u2

Common Equity (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 $ / shares | Sep. 30, 2019 $ / shares | Jun. 30, 2019 $ / shares | Mar. 31, 2019 $ / shares | Dec. 31, 2018 $ / shares | Sep. 30, 2018 $ / shares | Jun. 30, 2018 $ / shares | Mar. 31, 2018 $ / shares | Dec. 31, 2019 USD ($) $ / shares | Dec. 31, 2018 USD ($) $ / shares | Dec. 31, 2017 USD ($) $ / shares
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Common stock dividends declared |  |  |  |  |  |  |  |  | $ 47,842,000 | $ 45,762,000 | $ 43,682,000
Common stock dividends declared (in dollars per share) | $ / shares | $ 0.353 | $ 0.353 | $ 0.338 | $ 0.338 | $ 0.338 | $ 0.338 | $ 0.323 | $ 0.323 | $ 1.38 | $ 1.32 | $ 1.26
MGE [Member] |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Cash dividends paid to parent by MGE |  |  |  |  |  |  |  |  | $ 0 | $ 0 | $ 45,000,000
MGE [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Dividend restrictions, common equity ratio |  |  |  |  |  |  |  |  | 0.55 |  |

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