Pension Plans and Other Postretirement Benefits (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan, Deferred Pension and Other Postretirement Benefit Plan Costs Recovered [Abstract]
Deferred (recognized) pension and OPEB costs	$ (900)		$ 6,200
Pension Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	5,296	[1]	4,692	[1]	$ 5,723
Interest cost	12,210	[1]	14,302	[1]	12,859
Expected return on assets	(27,229)	[1]	(22,786)	[1]	(26,241)
Amortization of:
Transition obligation	0	[1]	0	[1]	0
Prior service (credit) cost	(114)	[1]	(117)	[1]	(44)
Actuarial loss	5,357	[1]	7,379	[1]	5,278
Net periodic benefit cost (credit)	(4,480)	[1]	3,470	[1]	(2,425)
Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	1,264	[1]	1,110	[1]	1,283
Interest cost	2,278	[1]	2,893	[1]	2,612
Expected return on assets	(3,154)	[1]	(2,723)	[1]	(3,232)
Amortization of:
Transition obligation	3	[1]	3	[1]	3
Prior service (credit) cost	(2,669)	[1]	(2,669)	[1]	(2,669)
Actuarial loss	217	[1]	401	[1]	488
Net periodic benefit cost (credit)	$ (2,061)	[1]	$ (985)	[1]	$ (1,515)

[1] During 2019, MGE deferred approximately $6.2 million of pension and other postretirement costs. During 2020, MGE collected approximately $0.9 million of pension and other postretirement costs, which reduced the amount deferred in 2019. The impact of the deferral has not been reflected in the table above. See Footnote 8 for further information.