Derivative and Hedging Instruments (Details-1) $ in Thousands		3 Months Ended	6 Months Ended	12 Months Ended
		Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($) Dth MWh MW	Dec. 31, 2019 USD ($) Dth MWh MW	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Derivative fair values [Abstract]
Collateral posted against derivative positions		$ 300	$ 300	$ 1,500
Other Current Assets [Member]
Derivative fair values [Abstract]
Derivative fair value, net		940	940	1,100	$ 430	$ 878	$ 259	$ 377
Commodity Contracts And Financial Transimission Rights [Member]
Derivative fair values [Abstract]
Derivative fair value, net		(100)	$ (100)	$ (1,400)
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh			413,320	417,840
Notional amount, decatherm measure (in Dth) | Dth			7,280,000	6,605,000
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		1,433	$ 1,433	$ 230
Liability Derivatives, fair value, gross basis		1,495	1,495	1,738
Collateral posted against derivative positions		319	319	1,546
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		300	300	100
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	1,281	1,281	157
Liability Derivatives, fair value, gross basis	[1],[2]	1,407	1,407	1,521
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	152	152	73
Liability Derivatives, fair value, gross basis	[1]	88	88	217
Commodity Derivative Contracts [Member] | Cash Flow Hedging [Member]
Derivative fair values [Abstract]
Collateral posted against derivative positions		$ 300	$ 300	$ 1,500
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			6,286	2,750
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		$ 42	$ 42	$ 73
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		42	42	73
Liability Derivatives, fair value, gross basis		0	$ 0	$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW			1,150	1,450
Derivative fair values [Abstract]
Derivative fair value, net		(20,400)	$ (20,400)	$ (25,400)
Liability Derivatives, fair value, gross basis		20,380	20,380	25,440
Collateral posted against derivative positions		0	0	0
PPA [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		10,430	10,430	10,100
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		$ 9,950	$ 9,950	$ 15,340

[1] As of June 30, 2020, and December 31, 2019, collateral of $0.3 million and $1.5 million, respectively, was posted against and netted with derivative liability positions on the consolidated balance sheets.

[2] As of June 30, 2020, and December 31, 2019, MGE posted $0.3 million and $0.1 million, respectively, as other current assets on the consolidated balance sheets.