Fair Value of Financial Instruments (Details-4) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance,		$ (33,337,000)	$ (37,332,000)	$ (32,002,000)	$ (42,026,000)
Realized and unrealized gains (losses):
Included in regulatory assets		4,317,000	2,018,000	2,982,000	6,711,000
Included in other comprehensive income		0	0	0	0
Included in earnings	[1]	(492,000)	26,000	(1,928,000)	(434,000)
Included in current assets		4,000	(25,000)	(198,000)	(496,000)
Purchases		5,205,000	5,736,000	16,827,000	17,602,000
Sales		0	0	0	0
Issuances		0	0	0	0
Settlements		(4,717,000)	(5,737,000)	(14,701,000)	(16,671,000)
Transfers in and/or out of level 3		0	0	0	0
Ending balance,		$ (29,020,000)	$ (35,314,000)	$ (29,020,000)	$ (35,314,000)

[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.