Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance,		$ (25,647)	$ (31,283)	$ (26,456)	$ (32,002)
Realized and unrealized gains (losses):
Included in regulatory assets		4,624	(2,054)	5,434	(1,335)
Included in other comprehensive income		0	0	0	0
Included in earnings	[1]	1,710	792	3,163	1,436
Included in current assets		(311)	(376)	(64)	(203)
Purchases		5,317	5,858	10,331	11,623
Sales		0	0	0	0
Issuances		0	0	0	0
Settlements		(3,296)	(4,690)	(7,105)	(9,984)
Transfers in and/or out of level 3		0	0	0	0
Ending balance,		$ (21,023)	$ (33,337)	$ (21,023)	$ (33,337)

[1] MGE's exchange-traded derivative contracts, over-the-counter party transactions, purchased power agreement, and FTRs are subject to regulatory deferral. These derivatives are therefore marked to fair value and are offset in the financial statements with a corresponding regulatory asset or liability.