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, 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		29,000
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		29,000
Stock Issued During Period, Value, Dividend Reinvestment Plan	2,591	$ 29	2,562
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
Beginning balance, shares at Dec. 31, 2024		36,490,000
Beginning balance, value at Dec. 31, 2024	1,230,138	$ 36,490	429,515	764,133	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	112,587			112,587
Common stock dividends declared	$ (50,230)			(50,230)
Stock Issued During Period, Shares, Dividend Reinvestment Plan	40,995	41,000
Stock Issued During Period, Value, Dividend Reinvestment Plan	$ 3,750	$ 41	3,709
Equity-based compensation plans and other - Shares		11,000
Issuance of common stock, net	3,750
Equity-based compensation plans and other	1,408	$ 11	1,397
Ending balance, shares at Sep. 30, 2025		36,542,000
Ending balance, value at Sep. 30, 2025	1,297,653	$ 36,542	434,621	826,490	0
Beginning balance, shares at Jun. 30, 2025		36,542,000
Beginning balance, value at Jun. 30, 2025	1,269,973	$ 36,542	434,080	799,351	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	44,497			44,497
Common stock dividends declared	(17,358)			(17,358)
Equity-based compensation plans and other	541		541
Ending balance, shares at Sep. 30, 2025		36,542,000
Ending balance, value at Sep. 30, 2025	$ 1,297,653	$ 36,542	$ 434,621	$ 826,490	$ 0