Derivative and Hedging Instruments (Details-1)		12 Months Ended
		Dec. 31, 2019 USD ($) Dth MWh MW	Dec. 31, 2018 USD ($) Dth MWh MW		Dec. 31, 2017 USD ($)
Derivative Fair Values [Abstract]
Collateral posted against derivative positions		$ 1,500,000
Other Current Assets [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		1,100,000	$ 377,000		$ 806,000
Commodity Contracts and Financial Transimission Rights [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		$ (1,400,000)	$ 700,000
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh		417,840	386,440
Notional amount, decatherm measure (in Dth) | Dth		6,605,000	5,260,000
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		$ 230,000	$ 801,000
Liability Derivatives, fair value, gross basis		1,738,000	342,000
Collateral posted against derivative positions		1,546,000	0
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		100,000	727,000	[1]
Liability Derivatives, fair value, gross basis	[1]		270,000
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]		74,000
Liability Derivatives, fair value, gross basis	[1]		72,000
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	157,000
Liability Derivatives, fair value, gross basis	[1],[2]	1,521,000
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	73,000
Liability Derivatives, fair value, gross basis	[1],[2]	217,000
Commodity Derivative Contracts [Member] | Cash Flow Hedging [Member]
Derivative Fair Values [Abstract]
Derivative, right to reclaim collateral (receivable)			$ 0
Collateral posted against derivative positions		$ 1,500,000
Energy Related Commodity Contract [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Maximum term of derivative hedging contract		4 years
Financial Transmission Rights [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		2,750	2,252
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		$ 73,000	$ 241,000
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		73,000	241,000
Liability Derivatives, fair value, gross basis		$ 0	$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		1,450	2,050
Derivative Fair Values [Abstract]
Derivative fair value, net		$ 25,400,000	$ 32,500,000
Liability Derivatives, fair value, gross basis		25,440,000	32,530,000
Collateral posted against derivative positions		0	0
PPA [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		10,100,000	8,550,000
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		$ 15,340,000	$ 23,980,000

[1] As of December 31, 2019, collateral of $1.5 million was posted against and netted with derivative liability positions on the consolidated balance sheets. No collateral was posted against derivative positions as of December 31, 2018.

[2] As of December 31, 2019, MGE posted $0.1 million as other current assets on the consolidated balance sheets.