MGE Energy Inc Consolidated Statements of Common Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance, shares at Dec. 31, 2013		34,668
Beginning balance, value at Dec. 31, 2013	$ 617,510	$ 34,668	$ 316,268	$ 266,197	$ 377
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	65,133			65,133
Other comprehensive income (loss)	56				56
Common stock dividends declared	(28,634)			(28,634)
Cash in lieu of fractional shares related to stock split	(80)			(80)
Ending balance, shares at Sep. 30, 2014		34,668
Ending balance, value at Sep. 30, 2014	653,985	$ 34,668	316,268	302,616	433
Beginning balance, shares at Dec. 31, 2014		34,668
Beginning balance, value at Dec. 31, 2014	659,401	$ 34,668	316,268	308,007	458
Cumulative effect of new accounting principle (See Footnote 4) at Dec. 31, 2014	(142)			(142)
Beginning balance, value - Adjusted at Dec. 31, 2014	659,259			307,865
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	60,111			60,111
Other comprehensive income (loss)	(180)				(180)
Common stock dividends declared	(29,816)			(29,816)
Ending balance, shares at Sep. 30, 2015		34,668
Ending balance, value at Sep. 30, 2015	$ 689,374	$ 34,668	$ 316,268	$ 338,160	$ 278