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/(Loss) [Member]
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	33,178			33,178
Other comprehensive income (loss)	(154)				(154)
Common stock dividends declared	(20,454)			(20,454)
Ending balance, shares at Jun. 30, 2016		34,668
Ending balance, value at Jun. 30, 2016	703,028	$ 34,668	316,268	351,889	203
Beginning balance, shares at Dec. 31, 2016		34,668
Beginning balance, value at Dec. 31, 2016	724,088	$ 34,668	316,268	372,950	202
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	34,843			34,843
Other comprehensive income (loss)	129				129
Common stock dividends declared	(21,321)			(21,321)
Ending balance, shares at Jun. 30, 2017		34,668
Ending balance, value at Jun. 30, 2017	$ 737,739	$ 34,668	$ 316,268	$ 386,472	$ 331