Common Equity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2025 USD ($) $ / shares shares	Dec. 31, 2024 USD ($) $ / shares	Dec. 31, 2023 USD ($) $ / shares
Class of Stock [Line Items]
Common stock dividends declared	$ 67,587	$ 63,596	$ 60,393
Common stock dividends declared (in dollars per share) | $ / shares	$ 1.85	$ 1.76	$ 1.67
Stock Issued During Period, Shares, Dividend Reinvestment Plan | shares	41,000
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan	$ 3,800
Dilutive securities | shares	37,293
MGE [Member]
Class of Stock [Line Items]
Cash dividends paid to parent by MGE	$ 51,500	$ 34,500
MGE [Member] | Minimum [Member]
Class of Stock [Line Items]
Dividend restrictions, common equity ratio	0.55