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, 2014		34,668
Beginning balance, value before adjustments at Dec. 31, 2014	$ 659,401			$ 308,007
Cumulative effect of new accounting principle at Dec. 31, 2014	(142)			(142)
Beginning balance, value at Dec. 31, 2014	659,259	$ 34,668	$ 316,268	307,865	$ 458
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	60,111			60,111
Other comprehensive 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
Beginning balance, shares at Dec. 31, 2015		34,668
Beginning balance, value at Dec. 31, 2015	690,458	$ 34,668	316,268	339,165	357
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	61,058			61,058
Other comprehensive loss	(143)				(143)
Common stock dividends declared	(31,115)			(31,115)
Ending balance, shares at Sep. 30, 2016		34,668
Ending balance, value at Sep. 30, 2016	$ 720,258	$ 34,668	$ 316,268	$ 369,108	$ 214