MGE Energy Inc Consolidated Statements of Common Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]
Beginning balance, shares at Dec. 31, 2018		34,668,000
Beginning balance, value at Dec. 31, 2018	$ 816,644	$ 34,668	$ 316,268	$ 465,708	$ 0
Increase (Decrease) in Equity [Roll Forward]
Net Income	86,874			86,874
Common stock dividends declared	(47,842)			(47,842)
Issuance of common stock, net	0
Ending balance, shares at Dec. 31, 2019		34,668,000
Ending balance, value at Dec. 31, 2019	855,676	$ 34,668	316,268	504,740	0
Increase (Decrease) in Equity [Roll Forward]
Net Income	92,418			92,418
Common stock dividends declared	$ (51,729)			(51,729)
Common stock issued during period	1,500,000	1,495,000
Issuance of common stock, net	$ 79,635	$ 1,495	78,140
Ending balance, shares at Dec. 31, 2020		36,163,000
Ending balance, value at Dec. 31, 2020	976,000	$ 36,163	394,408	545,429	0
Increase (Decrease) in Equity [Roll Forward]
Net Income	105,761			105,761
Common stock dividends declared	(54,788)			54,788
Issuance of common stock, net	0
Equity-based compensation plans and other	495		495
Ending balance, shares at Dec. 31, 2021		36,163,000
Ending balance, value at Dec. 31, 2021	$ 1,027,468	$ 36,163	$ 394,903	$ 596,402	$ 0