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] 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, 2018			34,668	17,348
Beginning balance, value at Dec. 31, 2018		$ 689,810		$ 17,348	$ 192,417	$ 338,591	$ 0	$ 141,454
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	$ 70,212	64,764				48,039		16,725
Capital contributions from parent		0
Distributions to parent from noncontrolling interest		(17,000)						(17,000)
Ending balance, shares at Sep. 30, 2019			34,668	17,348
Ending balance, value at Sep. 30, 2019		737,574		$ 17,348	192,417	386,630	0	141,179
Beginning balance, shares at Jun. 30, 2019			34,668	17,348
Beginning balance, value at Jun. 30, 2019		714,323		$ 17,348	192,417	363,493	0	141,065
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	30,657	28,751				23,137		5,614
Distributions to parent from noncontrolling interest		(5,500)						(5,500)
Ending balance, shares at Sep. 30, 2019			34,668	17,348
Ending balance, value at Sep. 30, 2019		737,574		$ 17,348	192,417	386,630	0	141,179
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	76,622	71,191				54,437		16,754
Capital contributions from parent		30,000			30,000
Distributions to parent from noncontrolling interest		(16,000)						(16,000)
Ending balance, shares at Sep. 30, 2020			36,163	17,348
Ending balance, value at Sep. 30, 2020		862,780		$ 17,348	252,917	451,458	0	141,057
Beginning balance, shares at Jun. 30, 2020			36,163	17,348
Beginning balance, value at Jun. 30, 2020		840,047		$ 17,348	252,917	426,718	0	143,064
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	$ 31,794	30,233				24,740		5,493
Distributions to parent from noncontrolling interest		(7,500)						(7,500)
Ending balance, shares at Sep. 30, 2020			36,163	17,348
Ending balance, value at Sep. 30, 2020		$ 862,780		$ 17,348	$ 252,917	$ 451,458	$ 0	$ 141,057