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Fair Value Measurements - Level 3 Quantitative Information (Details) $ in Thousands | Dec. 31, 2018 USD ($) $ / MWh | Dec. 31, 2017 USD ($) $ / MWh
--- | --- | ---
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | $ 1,113 | $ 1,982
Forward Contracts | Electricity forward contracts | Minimum |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | $ / MWh | 17.88 | 18.51
Forward Contracts | Electricity forward contracts | Maximum |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | $ / MWh | 37.03 | 38.75
Forward Contracts | Electricity forward contracts | Weighted-Average |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | $ / MWh | 26.10 | 27.89
Forward Contracts | Natural gas forward contracts | Minimum |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | $ / MWh | 1.79 | 2.33
Forward Contracts | Natural gas forward contracts | Maximum |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | $ / MWh | 2.92 | 3.11
Forward Contracts | Natural gas forward contracts | Weighted-Average |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | $ / MWh | 2.48 | 2.71
Forward Contracts | Significant Unobservable Inputs (Level 3) |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | $ 2 | $ 1,036
Liabilities | 8,216 | 19,292
Forward Contracts | Significant Unobservable Inputs (Level 3) | Electricity forward contracts |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | 0 | 21
Liabilities | 2,456 | 15,485
Forward Contracts | Significant Unobservable Inputs (Level 3) | Natural gas forward contracts |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | 2 | 1,015
Liabilities | $ 5,760 | $ 3,807

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