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]	Accumulated Other Comprehensive Income/(Loss) [Member]
Beginning balance, shares at Dec. 31, 2018		34,668
Beginning balance, value at Dec. 31, 2018	$ 816,644	$ 34,668	$ 316,268	$ 465,708	$ 0
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	39,554			39,554
Common stock dividends declared	(23,401)			(23,401)
Issuance of common stock, net	0
Ending balance, shares at Jun. 30, 2019		34,668
Ending balance, value at Jun. 30, 2019	832,797	$ 34,668	316,268	481,861	0
Beginning balance, shares at Mar. 31, 2019		34,668
Beginning balance, value at Mar. 31, 2019	828,950	$ 34,668	316,268	478,014	0
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	15,548			15,548
Common stock dividends declared	(11,701)			(11,701)
Ending balance, shares at Jun. 30, 2019		34,668
Ending balance, value at Jun. 30, 2019	832,797	$ 34,668	316,268	481,861	0
Beginning balance, shares at Dec. 31, 2019		34,668
Beginning balance, value at Dec. 31, 2019	855,676	$ 34,668	316,268	504,740	0
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	44,828			44,828
Common stock dividends declared	$ (24,968)			(24,968)
Common stock issued during period	1,500	1,495
Issuance of common stock, net	$ 79,635	$ 1,495	78,140
Ending balance, shares at Jun. 30, 2020		36,163
Ending balance, value at Jun. 30, 2020	955,171	$ 36,163	394,408	524,600	0
Beginning balance, shares at Mar. 31, 2020		34,668
Beginning balance, value at Mar. 31, 2020	869,492	$ 34,668	316,268	518,556	0
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	18,791			18,791
Common stock dividends declared	(12,747)			(12,747)
Common stock issued during period		1,495
Issuance of common stock, net	79,635	$ 1,495	78,140
Ending balance, shares at Jun. 30, 2020		36,163
Ending balance, value at Jun. 30, 2020	$ 955,171	$ 36,163	$ 394,408	$ 524,600	$ 0