Fair Value of Financial Instruments: (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
GOLDEN STATE WATER COMPANY \| Reported Value Measurement
Fair value of financial instruments
Long-term Debt, Fair Value	$ 284,607	$ 284,699
GOLDEN STATE WATER COMPANY \| Estimate of Fair Value Measurement
Fair value of financial instruments
Long-term Debt, Fair Value	357,174	$ 376,467
Mutual Funds \| Fair Value, Inputs, Level 1
Financial liabilities:
Long-term debt-GSWC	$ 19,100

Includes other investments and securities that are not at fair value as of the balance sheet date and those that are not accounted for under the equity method.

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