MGE Energy Inc Consolidated Statements of Common Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]
Beginning balance, shares at Dec. 31, 2022		36,163,000
Beginning balance, value at Dec. 31, 2022	$ 1,081,674	$ 36,163	$ 395,657	$ 649,854	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	97,616			97,616
Common stock dividends declared	(44,933)			(44,933)
Issuance of common stock, net	0
Equity-based compensation plans and other	896		896
Ending balance, shares at Sep. 30, 2023		36,163,000
Ending balance, value at Sep. 30, 2023	1,135,253	$ 36,163	396,553	702,537	0
Beginning balance, shares at Jun. 30, 2023		36,163,000
Beginning balance, value at Jun. 30, 2023	1,112,584	$ 36,163	396,281	680,140	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	37,857			37,857
Common stock dividends declared	(15,460)			(15,460)
Equity-based compensation plans and other	272		272
Ending balance, shares at Sep. 30, 2023		36,163,000
Ending balance, value at Sep. 30, 2023	1,135,253	$ 36,163	396,553	702,537	0
Beginning balance, shares at Dec. 31, 2023		36,163,000
Beginning balance, value at Dec. 31, 2023	1,140,073	$ 36,163	396,750	707,160	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	98,547			98,547
Common stock dividends declared	$ (47,210)			(47,210)
Stock Issued During Period, Shares, Dividend Reinvestment Plan	29,176	29,000
Stock Issued During Period, Value, Dividend Reinvestment Plan	$ 2,591	$ 29	2,562
Equity-based compensation plans and other - Shares		13,000
Issuance of common stock, net	2,591
Equity-based compensation plans and other	1,264	$ 13	1,251
Ending balance, shares at Sep. 30, 2024		36,205,000
Ending balance, value at Sep. 30, 2024	1,195,265	$ 36,205	400,563	758,497	0
Beginning balance, shares at Jun. 30, 2024		36,176,000
Beginning balance, value at Jun. 30, 2024	1,167,628	$ 36,176	397,614	733,838	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	40,939			40,939
Common stock dividends declared	$ (16,280)			(16,280)
Stock Issued During Period, Shares, Dividend Reinvestment Plan	29,176	29,000
Stock Issued During Period, Value, Dividend Reinvestment Plan	$ 2,591	$ 29	2,562
Issuance of common stock, net	2,600
Equity-based compensation plans and other	387		387
Ending balance, shares at Sep. 30, 2024		36,205,000
Ending balance, value at Sep. 30, 2024	$ 1,195,265	$ 36,205	$ 400,563	$ 758,497	$ 0