Madison Gas and Electric Company Consolidated Statements of Common Equity (Unaudited) - USD ($) shares 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				$ 377,000	$ (28,000)	$ (377,000)	$ 28,000
Beginning balance, shares at Dec. 31, 2017			34,668	17,348
Beginning balance, value at Dec. 31, 2017		632,774,000		$ 17,348,000	$ 192,417,000		282,135,000		(28,000)	$ 140,902,000
Beginning balance, value - Adjusted at Dec. 31, 2017	$ 778,187,000	632,774,000				$ 427,251,000	282,107,000	$ 0	0
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		34,859,000					23,548,000			11,311,000
Distributions to parent from noncontrolling interest		(13,500,000)								(13,500,000)
Ending balance, shares at Jun. 30, 2018			34,668	17,348
Ending balance, value at Jun. 30, 2018		654,133,000		$ 17,348,000	192,417,000		305,655,000		0	138,713,000
Beginning balance, shares at Mar. 31, 2018			34,668	17,348
Beginning balance, value at Mar. 31, 2018		643,530,000		$ 17,348,000	192,417,000		294,557,000		0	139,208,000
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		16,603,000					11,098,000			5,505,000
Distributions to parent from noncontrolling interest		(6,000,000)								(6,000,000)
Ending balance, shares at Jun. 30, 2018			34,668	17,348
Ending balance, value at Jun. 30, 2018		654,133,000		$ 17,348,000	192,417,000		305,655,000		0	138,713,000
Beginning balance, shares at Dec. 31, 2018			34,668	17,348
Beginning balance, value at Dec. 31, 2018		689,810,000		$ 17,348,000	192,417,000		338,591,000		0	141,454,000
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		36,013,000					24,902,000			11,111,000
Distributions to parent from noncontrolling interest		(11,500,000)								(11,500,000)
Ending balance, shares at Jun. 30, 2019			34,668	17,348
Ending balance, value at Jun. 30, 2019		714,323,000		$ 17,348,000	192,417,000		363,493,000		0	141,065,000
Beginning balance, shares at Mar. 31, 2019			34,668	17,348
Beginning balance, value at Mar. 31, 2019		704,380,000		$ 17,348,000	192,417,000		355,171,000		0	139,444,000
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		13,943,000					8,322,000			5,621,000
Distributions to parent from noncontrolling interest		(4,000,000)								(4,000,000)
Ending balance, shares at Jun. 30, 2019			34,668	17,348
Ending balance, value at Jun. 30, 2019		$ 714,323,000		$ 17,348,000	$ 192,417,000		$ 363,493,000		$ 0	$ 141,065,000