Regulatory Matters: (Details) $ in Thousands	3 Months Ended			9 Months Ended
	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2018
Regulatory matters:
Regulatory asset not accruing carrying costs	$ (42,700)
Water Revenue Adjustment Mechanism and Modified Cost Balancing Account
Regulatory matters:
Increase (Decrease) in Other Regulatory Assets				$ 4,700
Pension and other post-retirement obligations
Regulatory matters:
Regulatory asset not accruing carrying costs	(42,900)
GOLDEN STATE WATER COMPANY
Regulatory matters:
Regulatory assets	(1,867)				$ 2,450
GOLDEN STATE WATER COMPANY | Various refunds to customers
Regulatory matters:
Regulatory assets	$ 7,319				8,478
GOLDEN STATE WATER COMPANY | Cost of Capital, Proceeding for Water Regions [Member]
Regulatory matters:
Return on Equity Percentage	8.90%
Weighted Cost of Capital Percent	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		$ 2,200	$ 2,800
Regulatory assets	$ (25,011)				(22,535)
GOLDEN STATE WATER COMPANY | Costs deferred for future recovery on Aerojet case
Regulatory matters:
Regulatory assets	(8,097)				(8,292)
GOLDEN STATE WATER COMPANY | Pension and other post-retirement obligations
Regulatory matters:
Regulatory assets	(40,170)				(40,693)
GOLDEN STATE WATER COMPANY | Derivative [Member]
Regulatory matters:
Regulatory asset not accruing carrying costs	(4,300)
GOLDEN STATE WATER COMPANY | Derivative unrealized loss
Regulatory matters:
Regulatory assets	(4,280)				(3,171)
GOLDEN STATE WATER COMPANY | General Rate Case Memorandum Accounts
Regulatory matters:
Regulatory assets	(3,551)				(4,820)
GOLDEN STATE WATER COMPANY | Deferred Income Tax Charge
Regulatory matters:
Regulatory asset not accruing carrying costs	(79,500)
Regulatory assets	79,522				79,886
GOLDEN STATE WATER COMPANY | Flow-through taxes, net
Regulatory matters:
Regulatory asset not accruing carrying costs	(12,200)
Regulatory assets	12,246				12,439
GOLDEN STATE WATER COMPANY | Other Regulatory Assets Net [Member]
Regulatory matters:
Regulatory assets	(19,845)				$ (18,842)
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism [Member]
Regulatory matters:
Regulatory assets	$ (11,200)
Water Service Utility Operations [Member]
Regulatory matters:
Number of parties						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