Derivative and Hedging Instruments (Details-1) $ in Thousands		12 Months Ended
		Dec. 31, 2018 USD ($) Dth MWh MW		Dec. 31, 2017 USD ($) Dth MWh MW	Dec. 31, 2016 USD ($)
Derivative Fair Values [Abstract]
Derivative, right to reclaim collateral (receivable)		$ 0		$ 100
Other Current Assets [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		377		806	$ 230
Commodity Contracts and Financial Transimission Rights [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		$ 700		$ 200
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh		386,440		552,310
Notional amount, decatherm measure (in Dth) | Dth		5,260,000		5,460,000
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		$ 801		$ 676
Liability Derivatives, fair value, gross basis		342		793
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	727
Liability Derivatives, fair value, gross basis		270	[1]	100
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	74
Liability Derivatives, fair value, gross basis	[1]	$ 72
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1],[2]			566
Liability Derivatives, fair value, gross basis	[1],[2]			603
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]			110
Liability Derivatives, fair value, gross basis	[1]			$ 190
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		2,252		2,226
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		$ 241		$ 329
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		241		329
Liability Derivatives, fair value, gross basis		$ 0		$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		2,050		2,650
Derivative Fair Values [Abstract]
Derivative fair value, net		$ (32,500)		$ (42,200)
Liability Derivatives, fair value, gross basis		32,530		42,170
PPA [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		8,550		8,180
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		$ 23,980		$ 33,990

[1] As of December 31, 2017 , collateral of $ 0.1 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, 2017 , MGE presented $ 0.1 million as other current assets on the consolidated balance sheets.