Regulatory Matters: Alternative-Revenue Programs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Regulatory matters:
Regulatory assets	$ (1,213)		$ (1,213)		$ (2,450)
Water Revenue Adjustment Mechanism and Modified Cost Balancing Account
Regulatory matters:
Increase (decrease) in other regulatory assets			12,800
GOLDEN STATE WATER COMPANY
Regulatory matters:
Regulatory assets	(3,902)		$ (3,902)		(2,450)
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism and Modified Cost Balancing Account
Regulatory matters:
Commercial paper, term			90 days
Amount billed to customers as surcharges	4,400	$ 5,500	$ 10,500	$ 9,100
Regulatory assets	24,904		$ 24,904		$ 22,535
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism and Modified Cost Balancing Account | Minimum
Regulatory matters:
Regulatory Asset Recovery Periods			12 months
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism and Modified Cost Balancing Account | Maximum
Regulatory matters:
Regulatory Asset Recovery Periods			24 months
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism [Member]
Regulatory matters:
Regulatory assets	10,300		$ 10,300
GOLDEN STATE WATER COMPANY | Modified Cost Balancing Account
Regulatory matters:
Regulatory assets	$ 14,600		$ 14,600