Schedule I - Condensed Parent Company Finanical Statements (Details-Comprehensive Income Statement) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Operating Expenses:
Other operations and maintenance													$ 177,823	$ 177,740		$ 172,335
Total Operating Expenses	$ 116,089	$ 97,997	$ 100,031	$ 131,444	$ 115,077	[1]	$ 97,542	[1]	$ 100,868	[1]	$ 124,987	[1]	445,561	438,474		420,863
Operating Income (Loss)	23,990	39,798	24,231	26,188	25,197		41,997		25,595		31,836		114,207	124,625		123,882
Equity earnings of investments													8,821	10,125		8,428
Income before income taxes													111,653	119,700		118,073
Income tax provision	(5,642)	(9,597)	(5,828)	(6,367)	13,393	[2]	(15,584)	[2]	(8,736)	[2]	(11,167)	[2]	(27,434)	(22,094)	[2]	(42,513)
Net Income	$ 16,361	$ 29,506	$ 18,351	$ 20,001	$ 36,134		$ 26,629		$ 15,543		$ 19,300		84,219	97,606		75,560
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Unrealized gain (loss) on available for sale securities, net of tax													0	175		(155)
Comprehensive Income													84,219	97,781		75,405
MGE Energy [Member]
Operating Expenses:
Other operations and maintenance													913	880		720
Total Operating Expenses													913	880		720
Operating Income (Loss)													(913)	(880)		(720)
Equity earnings of investments													85,220	99,246		75,581
Other income/(loss), net													(1,966)	(2,165)		435
Interest income, net													1,489	605		176
Income before income taxes													83,830	96,806		75,472
Income tax provision													389	800		88
Net Income													84,219	97,606		75,560
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Unrealized gain (loss) on available for sale securities, net of tax													0	175		(155)
Comprehensive Income													$ 84,219	$ 97,781		$ 75,405

[1] Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for more information.

[2] In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information.