Derivative and Hedging Instruments (Details-1) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2020 USD ($) Dth MWh MW	Dec. 31, 2019 USD ($) Dth MWh MW	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Derivative fair values [Abstract]
Collateral posted against derivative positions		$ 1,700	$ 1,500
Other Current Assets [Member]
Derivative fair values [Abstract]
Derivative fair value, net		430	1,100	$ 259	$ 377
Commodity Contracts And Financial Transimission Rights [Member]
Derivative fair values [Abstract]
Derivative fair value, net		$ (1,700)	$ (1,400)
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh		498,960	417,840
Notional amount, decatherm measure (in Dth) | Dth		4,650,000	6,605,000
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		$ 673	$ 230
Liability Derivatives, fair value, gross basis		2,399	1,738
Collateral posted against derivative positions		1,747	1,546
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		300	100
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	599	157
Liability Derivatives, fair value, gross basis	[1],[2]	2,159	1,521
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	74	73
Liability Derivatives, fair value, gross basis	[1]	240	217
Commodity Derivative Contracts [Member] | Cash Flow Hedging [Member]
Derivative fair values [Abstract]
Collateral posted against derivative positions		$ 1,700	$ 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		1,108	2,750
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		$ 9	$ 73
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		9	73
Liability Derivatives, fair value, gross basis		$ 0	$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		1,300	1,450
Derivative fair values [Abstract]
Derivative fair value, net		$ (23,600)	$ (25,400)
Liability Derivatives, fair value, gross basis		23,610	25,440
Collateral posted against derivative positions		0	0
PPA [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		10,740	10,100
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		$ 12,870	$ 15,340

[1] As of March 31, 2020, and December 31, 2019, collateral of $1.7 million and $1.5 million, respectively, was posted against and netted with derivative liability positions on the consolidated balance sheets.

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