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]
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		32,333					21,548			10,785
Other comprehensive income (loss)	$ 129	(31)						$ 129	(31)
Cash dividends paid to parent by MGE		(25,000)					(25,000)
Distributions to parent from noncontrolling interest		(10,000)								(10,000)
Ending balance, shares at Jun. 30, 2017			34,668	17,348
Ending balance, value at Jun. 30, 2017		600,051		$ 17,348	192,417		273,848		(12)	116,450
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
Cumulative effect of new accounting principle at Dec. 31, 2017	0	0				$ 377	(28)	(377)	28
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		34,859					23,548			11,311
Distributions to parent from noncontrolling interest		(13,500)								(13,500)
Ending balance, shares at Jun. 30, 2018			34,668	17,348
Ending balance, value at Jun. 30, 2018		$ 654,133		$ 17,348	$ 192,417		$ 305,655		$ 0	$ 138,713