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	41,804			41,804
Other comprehensive income (loss)	(39)				(39)
Common stock dividends declared	(18,840)			(18,840)
Cash in lieu of fractional shares related to stock split	(80)			(80)
Ending balance, shares at Jun. 30, 2014		34,668
Ending balance, value at Jun. 30, 2014	640,355	$ 34,668	316,268	289,081	338
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	31,757			31,757
Other comprehensive income (loss)	(95)				(95)
Common stock dividends declared	(19,589)			(19,589)
Ending balance, shares at Jun. 30, 2015		34,668
Ending balance, value at Jun. 30, 2015	$ 671,332	$ 34,668	$ 316,268	$ 320,033	$ 363