Schedule I - Condensed Parent Company Finanical Statements (Details-Comprehensive Income Statement) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Expenses:
Other operations and maintenance									$ 186,430	$ 193,322	$ 177,823
Total Operating Expenses	$ 117,797	$ 96,886	$ 95,520	$ 118,433	$ 119,064	$ 99,460	$ 102,364	$ 137,057	428,636	457,945	445,561
Operating Income	18,712	38,325	21,520	31,440	21,877	38,738	19,783	30,512	109,997	110,910	114,207
Equity earnings of investments									10,221	9,889	8,821
Income before income taxes									111,841	106,658	111,653
Income tax provision	(3,370)	(7,300)	(3,740)	(5,013)	(3,116)	(7,454)	(3,505)	(5,709)	(19,423)	(19,784)	(27,434)
Net Income	$ 15,796	$ 31,794	$ 18,791	$ 26,037	$ 16,662	$ 30,657	$ 15,548	$ 24,007	92,418	86,874	84,219
MGE Energy [Member]
Operating Expenses:
Other operations and maintenance									882	815	913
Total Operating Expenses									882	815	913
Operating Income									(882)	(815)	(913)
Equity earnings of investments									92,922	87,728	85,220
Other income/(loss), net									94	(1,500)	(1,966)
Interest income, net									78	1,224	1,489
Income before income taxes									92,212	86,637	83,830
Income tax provision									206	237	389
Net Income									$ 92,418	$ 86,874	$ 84,219