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]	Retained Earnings [Member] MGE [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Accumulated Other Comprehensive Income/(Loss) [Member] MGE [Member]	Noncontrolling Interest [Member] MGE [Member]
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Cumulative effect of new accounting principle	$ 0	$ 0				$ 377	$ (28)	$ (377)	$ 28
Beginning balance, shares at Dec. 31, 2017			34,668	17,348
Beginning balance, value at Dec. 31, 2017		632,774		$ 17,348	$ 192,417		282,135		(28)	$ 140,902
Beginning balance, value - Adjusted at Dec. 31, 2017	778,187	632,774				$ 427,251	282,107	$ 0	0
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	67,858	62,775					45,835			16,940
Distributions to parent from noncontrolling interest		(19,000)								(19,000)
Ending balance, shares at Sep. 30, 2018			34,668	17,348
Ending balance, value at Sep. 30, 2018		676,549		$ 17,348	192,417		327,942		0	138,842
Beginning balance, shares at Jun. 30, 2018			34,668	17,348
Beginning balance, value at Jun. 30, 2018		654,133		$ 17,348	192,417		305,655		0	138,713
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	29,506	27,916					22,287			5,629
Distributions to parent from noncontrolling interest		(5,500)								(5,500)
Ending balance, shares at Sep. 30, 2018			34,668	17,348
Ending balance, value at Sep. 30, 2018		676,549		$ 17,348	192,417		327,942		0	138,842
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
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