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]	Accumulated Other Comprehensive Income/(Loss) [Member] MGE [Member]	Noncontrolling Interest [Member] MGE [Member]
Beginning balance, shares at Dec. 31, 2015			34,668	17,348
Beginning balance, value at Dec. 31, 2015		$ 641,984		$ 17,348	$ 192,417	$ 291,888		$ 23	$ 140,308
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		60,949				43,050			17,899
Other comprehensive income (loss)	$ (143)	(31)					$ (143)	(31)
Cash dividends paid to parent by MGE		(40,000)				(40,000)
Equity contribution received by noncontrolling interest		1,598							1,598
Distributions to parent from noncontrolling interest		(18,113)							(18,113)
Deconsolidation of noncontrolling interest		(25,486)							(25,486)
Ending balance, shares at Sep. 30, 2016			34,668	17,348
Ending balance, value at Sep. 30, 2016		620,901		$ 17,348	192,417	294,938		(8)	116,206
Beginning balance, shares at Dec. 31, 2016			34,668	17,348
Beginning balance, value at Dec. 31, 2016		602,749		$ 17,348	192,417	277,300		19	115,665
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		57,686				41,462			16,224
Other comprehensive income (loss)	$ 189	(38)					$ 189	(38)
Cash dividends paid to parent by MGE		(35,000)				(35,000)
Distributions to parent from noncontrolling interest		(16,500)							(16,500)
Ending balance, shares at Sep. 30, 2017			34,668	17,348
Ending balance, value at Sep. 30, 2017		$ 608,897		$ 17,348	$ 192,417	$ 283,762		$ (19)	$ 115,389