Common Equity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares
Class of Stock [Line Items]
Common stock dividends declared | $	$ 57,500	$ 54,788	$ 51,729
Common stock dividends declared (in dollars per share) | $ / shares	$ 1.59	$ 1.52	$ 1.45
Common stock issued during period under the stock plan | shares	0	0
Dilutive securities | shares	10,949
MGE [Member]
Class of Stock [Line Items]
Cash dividends paid to parent by MGE | $	$ 33,500	$ 5,000
MGE [Member] | Minimum [Member]
Class of Stock [Line Items]
Dividend restrictions, common equity ratio	0.55