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Derivative Instruments (Details) - GOLDEN STATE WATER COMPANY $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2019 | Jun. 30, 2019 USD ($) | Jun. 30, 2018 USD ($) | Jun. 30, 2019 USD ($) MWh | Jun. 30, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |  |
Description of derivative activity volume | MWh |  |  |  | 44,064 |  |  |
Commodity Contract |  |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |  |
Term of derivative contract |  |  |  |  |  | 3 years |
Number of broker quotes received to determine fair value of derivative instrument |  | 1 |  | 1 |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |
Fair value at beginning of the period |  | $ (336) | $ (2,625) | $ (311) | $ (2,941) |  |
Unrealized gain on purchased power contracts |  | 69 | 915 | 44 | 1,231 |  |
Fair value at end of the period |  | $ (267) | $ (1,710) | $ (267) | $ (1,710) | $ (2,941) |
Minimum | Commodity Contract |  |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |  |
Term of derivative contract |  |  |  |  |  |  | 3 years
Maximum | Commodity Contract |  |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |  |
Term of derivative contract |  |  |  |  |  |  | 5 years
Subsequent Event [Member] | Commodity Contract |  |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |  |
Term of derivative contract | 5 years |  |  |  |  |  |

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