Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance		$ (26,456)	$ (32,002)	$ (42,026)
Realized and unrealized gains (losses):
Included in regulatory asset		12,402	5,545	10,024
Included in other comprehensive income		0	0	0
Included in earnings	[1]	(6,439)	(3,765)	132
Included in current assets		(87)	(70)	(47)
Purchases		22,232	22,974	23,643
Sales		0	0	0
Issuances		0	0	0
Settlements		(15,707)	(19,138)	(23,728)
Transfers in and/or out of Level 3		0	0	0
Ending balance		$ (14,055)	$ (26,456)	$ (32,002)

[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.