MGE Energy Inc Consolidated Statements of Common Equity (Unaudited) - USD ($) shares in Thousands, $ 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, 2020		36,163
Beginning balance, value at Dec. 31, 2020	$ 976,000	$ 36,163	$ 394,408	$ 545,429	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	57,784			57,784
Common stock dividends declared	(26,761)			(26,761)
Equity-based compensation plans and other	278		278
Ending balance, shares at Jun. 30, 2021		36,163
Ending balance, value at Jun. 30, 2021	1,007,301	$ 36,163	394,686	576,452	0
Beginning balance, shares at Mar. 31, 2021		36,163
Beginning balance, value at Mar. 31, 2021	997,711	$ 36,163	394,566	566,982	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	22,851			22,851
Common stock dividends declared	(13,381)			(13,381)
Equity-based compensation plans and other	120		120
Ending balance, shares at Jun. 30, 2021		36,163
Ending balance, value at Jun. 30, 2021	1,007,301	$ 36,163	394,686	576,452	0
Beginning balance, shares at Dec. 31, 2021		36,163
Beginning balance, value at Dec. 31, 2021	1,027,468	$ 36,163	394,903	596,402	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	56,181			56,181
Common stock dividends declared	(28,027)			(28,027)
Equity-based compensation plans and other	435		435
Ending balance, shares at Jun. 30, 2022		36,163
Ending balance, value at Jun. 30, 2022	1,056,057	$ 36,163	395,338	624,556	0
Beginning balance, shares at Mar. 31, 2022		36,163
Beginning balance, value at Mar. 31, 2022	1,048,153	$ 36,163	395,181	616,809	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	21,761			21,761
Common stock dividends declared	(14,014)			(14,014)
Equity-based compensation plans and other	157		157
Ending balance, shares at Jun. 30, 2022		36,163
Ending balance, value at Jun. 30, 2022	$ 1,056,057	$ 36,163	$ 395,338	$ 624,556	$ 0