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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.

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