Regulatory Matters: (Details) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020 USD ($)	Mar. 31, 2020	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Regulatory matters:
Regulatory asset not accruing carrying costs	$ (44,900)			$ (44,900)
Regulatory assets	1,213			1,213		$ 2,450
Pension and other post-retirement obligations
Regulatory matters:
Regulatory asset not accruing carrying costs	(41,700)			(41,700)
Water Revenue Adjustment Mechanism Net of Modified Cost Balancing Account [Member]
Regulatory matters:
Increase (Decrease) in Other Regulatory Assets				12,800
Bear Valley Electric Service, Inc. | Derivative unrealized loss
Regulatory matters:
Regulatory assets	(2,518)			(2,518)		0
Bear Valley Electric Service, Inc. | Other Regulatory Assets Net [Member]
Regulatory matters:
Regulatory assets	(171)			(171)		0
Golden State Water Company
Regulatory matters:
Regulatory assets	3,902			3,902		2,450
Golden State Water Company | Revenue Subject to Refund [Member]
Regulatory matters:
Regulatory assets	$ 3,620			$ 3,620		8,478
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 | Costs deferred for future recovery on Aerojet case
Regulatory matters:
Regulatory assets	$ (7,169)			$ (7,169)		(8,292)
Golden State Water Company | Pension and other post-retirement obligations
Regulatory matters:
Regulatory assets	(40,606)			(40,606)		(40,693)
Golden State Water Company | Derivative [Member]
Regulatory matters:
Regulatory asset not accruing carrying costs	(2,500)			(2,500)
Golden State Water Company | Derivative unrealized loss
Regulatory matters:
Regulatory assets	0			0		(3,171)
Golden State Water Company | General Rate Case Memorandum Accounts
Regulatory matters:
Regulatory assets	(218)			(218)		(4,820)
Golden State Water Company | Deferred Income Tax Charge
Regulatory matters:
Regulatory asset not accruing carrying costs	(78,800)			(78,800)
Regulatory assets	74,597			74,597		79,886
Golden State Water Company | Flow-through taxes, net
Regulatory matters:
Regulatory asset not accruing carrying costs	(11,500)			(11,500)
Regulatory assets	10,809			10,809		12,439
Golden State Water Company | Water Revenue Adjustment Mechanism [Member]
Regulatory matters:
Regulatory assets	(10,300)			(10,300)
Golden State Water Company | Other Regulatory Assets Net [Member]
Regulatory matters:
Regulatory assets	(12,227)			(12,227)		(18,842)
Golden State Water Company | Water Revenue Adjustment Mechanism Net of Modified Cost Balancing Account [Member]
Regulatory matters:
Amount billed to customers as surcharges	4,400		$ 5,500	10,500	$ 9,100
Regulatory assets	$ (24,904)			$ (24,904)		$ (22,535)
Water Service Utility Operations [Member]
Regulatory matters:
Number of parties	3			3
Maximum [Member] | Golden State Water Company | Water Revenue Adjustment Mechanism Net of Modified Cost Balancing Account [Member]
Regulatory matters:
Regulatory Asset Recovery Periods				24 months
Minimum [Member] | Golden State Water Company | Water Revenue Adjustment Mechanism Net of Modified Cost Balancing Account [Member]
Regulatory matters:
Regulatory Asset Recovery Periods				12 months