Fair Value of Financial Instruments (Details-5) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	[1]	$ 0	$ 0	$ 0	$ 0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in earnings	[1]	(492,000)	26,000	(1,928,000)	(434,000)
Purchased Power Expense [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in earnings	[1]	(409,000)	26,000	(1,658,000)	(637,000)
Cost Of Gas Sold Expense [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in earnings	[1]	$ (83,000)	$ 0	$ (270,000)	$ 203,000

[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.