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Fair Value Measurements - Level 3 Quantitative Information (Details) - Forward Contracts $ in Thousands | Dec. 31, 2019 USD ($) $ / MWh | Dec. 31, 2018 USD ($) $ / MWh
--- | --- | ---
Electricity forward contracts | Minimum |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Significant Unobservable Input | $ / MWh | 22.18 | 17.88
Electricity forward contracts | Maximum |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Significant Unobservable Input | $ / MWh | 22.18 | 37.03
Electricity forward contracts | Weighted-Average |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Significant Unobservable Input | $ / MWh | 22.18 | 26.10
Natural gas forward contracts | Minimum |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Significant Unobservable Input | $ / MWh | 2.33 | 1.79
Natural gas forward contracts | Maximum |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Significant Unobservable Input | $ / MWh | 2.78 | 2.92
Natural gas forward contracts | Weighted-Average |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Significant Unobservable Input | $ / MWh | 2.49 | 2.48
(Level 3) |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | $ | $ 33 | $ 2
Financial and NonFinancial Liabilities, Fair Value Disclosure | $ | 3,429 | 8,216
(Level 3) | Electricity forward contracts |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | $ | 33 | 0
Financial and NonFinancial Liabilities, Fair Value Disclosure | $ | 819 | 2,456
(Level 3) | Natural gas forward contracts |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | $ | 0 | 2
Financial and NonFinancial Liabilities, Fair Value Disclosure | $ | $ 2,610 | $ 5,760

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