Madison Gas and Electric Company Consolidated Statements of Equity - 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]
Increase (Decrease) in Equity [Roll Forward]
Cumulative effect of new accounting principle	$ (142)	$ (142)					$ (142)	$ (142)
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
Beginning balance, value - Adjusted at Dec. 31, 2014	659,259	612,118					$ 307,865	276,520
Increase (Decrease) in Equity [Roll Forward]
Net Income		71,465						45,368			26,097
Other comprehensive income (loss)	(101)	(121)							$ (101)	(121)
Cash dividends paid to parent by MGE		(30,000)						(30,000)
Dividend in kind to parent		0
Equity contribution received by noncontrolling interest		3,230									3,230
Distributions to parent from noncontrolling interest		(14,708)									(14,708)
Ending balance, shares at Dec. 31, 2015				34,668	17,348
Ending balance, value at Dec. 31, 2015		641,984			$ 17,348	192,417		291,888		23	140,308
Increase (Decrease) in Equity [Roll Forward]
Net Income		74,592						51,234			23,358
Other comprehensive income (loss)	(155)	(4)							(155)	(4)
Cash dividends paid to parent by MGE		(50,000)	[1]					(50,000)
Dividend in kind to parent		(15,822)						(15,822)
Equity contribution received by noncontrolling interest		1,598									1,598
Distributions to parent from noncontrolling interest		(24,113)									(24,113)
Deconsolidation of noncontrolling interest		(25,486)									(25,486)
Ending balance, shares at Dec. 31, 2016				34,668	17,348
Ending balance, value at Dec. 31, 2016		602,749			$ 17,348	192,417		277,300		19	115,665
Increase (Decrease) in Equity [Roll Forward]
Net Income		93,072						49,835			43,237
Other comprehensive income (loss)	$ 175	(47)							$ 175	(47)
Cash dividends paid to parent by MGE		(45,000)						(45,000)
Dividend in kind to parent		0
Distributions to parent from noncontrolling interest		(18,000)									(18,000)
Ending balance, shares at Dec. 31, 2017				34,668	17,348
Ending balance, value at Dec. 31, 2017		$ 632,774			$ 17,348	$ 192,417		$ 282,135		$ (28)	$ 140,902

[1] Excludes $15.8 million dividend in kind to MGE Energy from MGE in 2016 .