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	24,007			24,007
Common stock dividends declared	(11,701)			(11,701)
Ending balance, shares at Mar. 31, 2019		34,668
Ending balance, value at Mar. 31, 2019	828,950	$ 34,668	316,268	478,014	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	26,037			26,037
Common stock dividends declared	(12,221)			(12,221)
Ending balance, shares at Mar. 31, 2020		34,668
Ending balance, value at Mar. 31, 2020	$ 869,492	$ 34,668	$ 316,268	$ 518,556	$ 0