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 at Dec. 31, 2014	$ 659,401	$ 34,668	$ 316,268	$ 308,007	$ 458
Cumulative effect of new accounting principle 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	18,278			18,278
Other comprehensive loss	(85)				(85)
Common stock dividends declared	(9,794)			(9,794)
Ending balance, shares at Mar. 31, 2015		34,668
Ending balance, value at Mar. 31, 2015	667,658	$ 34,668	316,268	316,349	373
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	17,028			17,028
Other comprehensive loss	(164)				(164)
Common stock dividends declared	(10,227)			(10,227)
Ending balance, shares at Mar. 31, 2016		34,668
Ending balance, value at Mar. 31, 2016	$ 697,095	$ 34,668	$ 316,268	$ 345,966	$ 193