MGE Energy Inc Consolidated Statements of Common Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance, value at Dec. 31, 2013	$ 617,510	$ 34,668	$ 316,268	$ 266,197	$ 377
Beginning balance, shares at Dec. 31, 2013		34,668
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	27,717			27,717
Other comprehensive income (loss)	7				7
Common stock dividends declared	(9,420)			(9,420)
Cash in lieu of fractional shares related to stock split	(80)			(80)
Ending balance, value at Mar. 31, 2014	635,734	34,668	316,268	284,414	384
Ending balance, shares at Mar. 31, 2014		34,668
Beginning balance, value at Dec. 31, 2014	659,401	34,668	316,268	308,007	458
Beginning balance, shares at Dec. 31, 2014		34,668
Beginning balance, value - Adjusted at Dec. 31, 2014	659,259			307,865
Cumulative effect of new accounting principle (See Footnote 4) at Dec. 31, 2014	(142)			(142)
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	18,278			18,278
Other comprehensive income (loss)	(85)				(85)
Common stock dividends declared	(9,794)			(9,794)
Ending balance, value at Mar. 31, 2015	$ 667,658	$ 34,668	$ 316,268	$ 316,349	$ 373
Ending balance, shares at Mar. 31, 2015		34,668