Regulatory Matters: (Details) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Regulatory matters:
Regulatory asset not accruing carrying costs	$ (42,800)			$ (42,800)
Water Revenue Adjustment Mechanism and Modified Cost Balancing Account
Regulatory matters:
Increase (Decrease) in Other Regulatory Assets				13,000
Pension and other post-retirement obligations
Regulatory matters:
Regulatory asset not accruing carrying costs	(42,200)			(42,200)
GOLDEN STATE WATER COMPANY
Regulatory matters:
Regulatory assets	(6,036)			(6,036)		$ 2,450
GOLDEN STATE WATER COMPANY | Various refunds to customers
Regulatory matters:
Regulatory assets	6,722			6,722		8,478
GOLDEN STATE WATER COMPANY | Catastrophic Event Memo Account (CEMA) [Member]
Regulatory matters:
Regulatory assets	$ (669)			$ (669)
GOLDEN STATE WATER COMPANY | Cost of Capital, Proceeding for Water Regions [Member]
Regulatory matters:
Return on Equity Percentage	8.90%			8.90%
Weighted Cost of Capital Percent	7.91%			7.91%
Extend filing term		1 year
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism and Modified Cost Balancing Account
Regulatory matters:
Amount billed to customers as surcharges	$ 3,800		$ 832	$ 6,100	$ 3,600
Regulatory assets	(29,495)			(29,495)		(22,535)
GOLDEN STATE WATER COMPANY | Costs deferred for future recovery on Aerojet case
Regulatory matters:
Regulatory assets	(7,745)			(7,745)		(8,292)
GOLDEN STATE WATER COMPANY | Pension and other post-retirement obligations
Regulatory matters:
Regulatory assets	(40,850)			(40,850)		(40,693)
GOLDEN STATE WATER COMPANY | Derivative [Member]
Regulatory matters:
Regulatory asset not accruing carrying costs	(3,800)			(3,800)
GOLDEN STATE WATER COMPANY | Derivative unrealized loss
Regulatory matters:
Regulatory assets	(3,827)			(3,827)		(3,171)
GOLDEN STATE WATER COMPANY | General Rate Case Memorandum Accounts
Regulatory matters:
Regulatory assets	(2,035)			(2,035)		(4,820)
GOLDEN STATE WATER COMPANY | Deferred Income Tax Charge
Regulatory matters:
Regulatory asset not accruing carrying costs	(79,200)			(79,200)
Regulatory assets	79,158			79,158		79,886
GOLDEN STATE WATER COMPANY | Flow-through taxes, net
Regulatory matters:
Regulatory asset not accruing carrying costs	(11,800)			(11,800)
Regulatory assets	11,788			11,788		12,439
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism [Member]
Regulatory matters:
Regulatory assets	(15,700)			(15,700)
GOLDEN STATE WATER COMPANY | Other Regulatory Assets Net [Member]
Regulatory matters:
Regulatory assets	$ (19,752)			$ (19,752)		$ (18,842)
Water Service Utility Operations [Member]
Regulatory matters:
Number of parties	3			3
Maximum [Member] | GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism and Modified Cost Balancing Account
Regulatory matters:
Regulatory Asset Recovery Periods				24 months
Minimum [Member] | GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism and Modified Cost Balancing Account
Regulatory matters:
Regulatory Asset Recovery Periods				12 months