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		18,256					12,450			5,806
Distributions to parent from noncontrolling interest		(7,500)								(7,500)
Ending balance, shares at Mar. 31, 2018			34,668	17,348
Ending balance, value at Mar. 31, 2018		643,530		$ 17,348	192,417		294,557		0	139,208
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		22,070					16,580			5,490
Distributions to parent from noncontrolling interest		(7,500)								(7,500)
Ending balance, shares at Mar. 31, 2019			34,668	17,348
Ending balance, value at Mar. 31, 2019		$ 704,380		$ 17,348	$ 192,417		$ 355,171		$ 0	$ 139,444