Madison Gas and Electric Company Consolidated Statements of Common Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	MGE [Member]	Common Stock [Member]	Common Stock [Member] MGE [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] MGE [Member]	Retained Earnings [Member] MGE [Member]	Accumulated Other Comprehensive Income/(Loss) [Member] MGE [Member]	Noncontrolling Interest [Member] MGE [Member]
Beginning balance, shares at Dec. 31, 2019			34,668	17,348
Beginning balance, value at Dec. 31, 2019		$ 777,589		$ 17,348		$ 222,917	$ 397,021	$ 0	$ 140,303
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	$ 26,037	24,557					19,064		5,493
Distributions to parent from noncontrolling interest		(7,000)							(7,000)
Ending balance, shares at Mar. 31, 2020			34,668	17,348
Ending balance, value at Mar. 31, 2020		795,146		$ 17,348		222,917	416,085	0	138,796
Beginning balance, shares at Dec. 31, 2020			36,163	17,348
Beginning balance, value at Dec. 31, 2020		871,612		$ 17,348		252,917	460,151	0	141,196
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	34,933	33,774					28,273		5,501
Distributions to parent from noncontrolling interest		(5,000)							(5,000)
Equity-based compensation plans and other	$ 158				$ 158
Ending balance, shares at Mar. 31, 2021			36,163	17,348
Ending balance, value at Mar. 31, 2021		$ 900,386		$ 17,348		$ 252,917	$ 488,424	$ 0	$ 141,697