Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance		$ (32,002)	$ (42,026)	$ (50,306)
Realized and unrealized gains (losses):
Included in regulatory liabilities		5,545	10,024	8,281
Included in other comprehensive income		0	0	0
Included in earnings	[1]	(3,765)	132	(3,718)
Included in current assets		(70)	(47)	(9)
Purchases		22,974	23,643	24,181
Sales		0	0	0
Issuances		0	0	0
Settlements		(19,138)	(23,728)	(20,455)
Transfers in and/or out of Level 3		0	0	0
Ending balance		$ (26,456)	$ (32,002)	$ (42,026)

[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.