Fair Value of Financial Instruments (Details-5) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities		$ 0	$ 0	$ 0	$ 0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in earnings	[1]	1,710	792	3,163	1,436
Purchased Power Expense [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in earnings		1,663	693	2,847	1,249
Cost Of Gas Sold Expense [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in earnings		$ 47	$ 99	$ 316	$ 187

[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.