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Derivative Instruments (Details) - GOLDEN STATE WATER COMPANY $ in Thousands | 1 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Dec. 31, 2014 USD ($) | Sep. 30, 2016 USD ($) MWh quote | Sep. 30, 2015 USD ($) | Sep. 30, 2016 USD ($) quote | Sep. 30, 2015 USD ($)
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |
Description of derivative activity volume | MWh |  | 396,000 |  |  |
Commodity Contract |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |
Number of broker quotes received to determine fair value of derivative instrument | quote |  | 1 |  | 1 |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value at beginning of the period |  | $ (4,933) | $ (5,662) | $ (7,053) | $ (3,339)
Unrealized gain (loss) on purchased power contracts |  | (648) | (1,584) | 1,472 | (3,907)
Fair value at end of the period | $ (3,339) | $ (5,581) | $ (7,246) | $ (5,581) | $ (7,246)
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 |  |  |  |

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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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