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Derivative Instruments (Details) MWh in Thousands, $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 USD ($) MWh | Dec. 31, 2018 USD ($)
Purchase power contract |  |
Changes in the fair value of the derivative |  |
Balance, at end of the period | $ (3,200) |
GSWC |  |
Derivative instruments |  |
Derivative Activity Volume | MWh | 638 |
GSWC | Purchase power contract |  |
Changes in the fair value of the derivative |  |
Balance, at beginning of the period | $ 311 | $ 2,941
Unrealized (loss) gain on purchased power contracts | (2,860) | 2,630
Balance, at end of the period | $ (3,171) | $ 311
Minimum | GSWC | Purchase power contract |  |
Derivative instruments |  |
Derivative, Term of Contract | 3 years |
Maximum | GSWC | Purchase power contract |  |
Derivative instruments |  |
Derivative, Term of Contract | 5 years |

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- Definition Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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