Schedule I - Condensed Parent Company Finanical Statements (Details-Comprehensive Income Statement) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Expenses:
Other operations and maintenance									$ 193,322	$ 177,823	$ 177,740
Total Operating Expenses	$ 119,064	$ 99,460	$ 102,364	$ 137,057	$ 116,089	$ 97,997	$ 100,031	$ 131,444	457,945	445,561	438,474
Operating Income (Loss)	21,877	38,738	19,783	30,512	23,990	39,798	24,231	26,188	110,910	114,207	124,625
Equity earnings of investments									9,889	8,821	10,125
Income before income taxes									106,658	111,653	119,700
Income tax provision	(3,116)	(7,454)	(3,505)	(5,709)	(5,642)	(9,597)	(5,828)	(6,367)	(19,784)	(27,434)	(22,094)	[1]
Net Income	$ 16,662	$ 30,657	$ 15,548	$ 24,007	$ 16,361	$ 29,506	$ 18,351	$ 20,001	86,874	84,219	97,606
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Unrealized gain (loss) on available for sale securities, net of tax									0	0	175
Comprehensive Income									86,874	84,219	97,781
MGE Energy [Member]
Operating Expenses:
Other operations and maintenance									815	913	880
Total Operating Expenses									815	913	880
Operating Income (Loss)									(815)	(913)	(880)
Equity earnings of investments									87,728	85,220	99,246
Other income/(loss), net									(1,500)	(1,966)	(2,165)
Interest income, net									1,224	1,489	605
Income before income taxes									86,637	83,830	96,806
Income tax provision									237	389	800
Net Income									86,874	84,219	97,606
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Unrealized gain (loss) on available for sale securities, net of tax									0	0	175
Comprehensive Income									$ 86,874	$ 84,219	$ 97,781

[1] In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act.