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 (Loss)/Income [Member]	Accumulated Other Comprehensive (Loss)/Income [Member] MGE [Member]	Noncontrolling Interest [Member] MGE [Member]
Beginning balance, shares at Dec. 31, 2013			34,668	17,348
Beginning balance, value at Dec. 31, 2013		$ 576,454		$ 17,348	$ 192,417		$ 247,534		$ 192	$ 118,963
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		65,255					45,471			19,784
Other comprehensive income (loss)	$ 56	(54)						$ 56	(54)
Cash dividends paid to parent by MGE		(26,500)					(26,500)
Equity contribution received by noncontrolling interest		1,420								1,420
Distributions to parent from noncontrolling interest		(17,778)								(17,778)
Ending balance, shares at Sep. 30, 2014			34,668	17,348
Ending balance, value at Sep. 30, 2014		598,797		$ 17,348	192,417		266,505		138	122,389
Beginning balance, shares at Dec. 31, 2014			34,668	17,348
Beginning balance, value at Dec. 31, 2014		612,260		$ 17,348	192,417		276,662		144	125,689
Cumulative effect of new accounting principle (See Footnote 4) at Dec. 31, 2014	(142)	(142)				$ (142)	(142)
Beginning balance, value - Adjusted at Dec. 31, 2014		612,118					276,520
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		60,240					40,428			19,812
Other comprehensive income (loss)	$ (180)	(137)						$ (180)	(137)
Cash dividends paid to parent by MGE		(20,000)					(20,000)
Equity contribution received by noncontrolling interest		3,053								3,053
Distributions to parent from noncontrolling interest		(12,007)								(12,007)
Ending balance, shares at Sep. 30, 2015			34,668	17,348
Ending balance, value at Sep. 30, 2015		$ 643,267		$ 17,348	$ 192,417		$ 296,948		$ 7	$ 136,547