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	61,058			61,058
Other comprehensive income (loss)	(143)				(143)
Common stock dividends declared	(31,115)			(31,115)
Ending balance, shares at Sep. 30, 2016		34,668
Ending balance, value at Sep. 30, 2016	720,258	$ 34,668	316,268	369,108	214
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	61,472			61,472
Other comprehensive income (loss)	189				189
Common stock dividends declared	(32,502)			(32,502)
Ending balance, shares at Sep. 30, 2017		34,668
Ending balance, value at Sep. 30, 2017	$ 753,247	$ 34,668	$ 316,268	$ 401,920	$ 391