MGE Energy Inc Consolidated Statements of Common Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss)/ 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 Common Equity [Roll Forward]
Net Income	80,319			80,319
Other comprehensive income (loss)	81				81
Common stock dividends declared	(38,429)			(38,429)
Cash in lieu of fractional shares related to stock split	(80)			(80)
Ending balance, shares at Dec. 31, 2014		34,668
Ending balance, value at Dec. 31, 2014	659,401	$ 34,668	316,268	308,007	458
Increase (Decrease) in Common Equity [Roll Forward]
Cumulative effect of new accounting principle	(142)			(142)
Beginning balance, value - Adjusted at Dec. 31, 2014	659,259			307,865
Increase (Decrease) in Common Equity [Roll Forward]
Net Income	71,343			71,343
Other comprehensive income (loss)	(101)				(101)
Common stock dividends declared	(40,043)			(40,043)
Ending balance, shares at Dec. 31, 2015		34,668
Ending balance, value at Dec. 31, 2015	690,458	$ 34,668	316,268	339,165	357
Increase (Decrease) in Common Equity [Roll Forward]
Net Income	75,560			75,560
Other comprehensive income (loss)	(155)				(155)
Common stock dividends declared	(41,775)			(41,775)
Ending balance, shares at Dec. 31, 2016		34,668
Ending balance, value at Dec. 31, 2016	$ 724,088	$ 34,668	$ 316,268	$ 372,950	$ 202