Regulatory Matters: (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Regulatory matters:
Regulatory asset not accruing carrying costs	$ 59,100
Pension and other post-retirement obligations
Regulatory matters:
Regulatory asset not accruing carrying costs	34,200
GOLDEN STATE WATER COMPANY
Regulatory matters:
Regulatory assets	(4,728)		$ 2,042
GOLDEN STATE WATER COMPANY | Revenue Subject to Refund
Regulatory matters:
Regulatory assets	(9,592)		(4,552)
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account
Regulatory matters:
Amount billed to customers as surcharges	4,200	$ 4,000
Regulatory assets	29,011		29,556
GOLDEN STATE WATER COMPANY | Costs deferred for future recovery on Aerojet case
Regulatory matters:
Regulatory assets	10,510		10,656
GOLDEN STATE WATER COMPANY | Pension and other post-retirement obligations
Regulatory matters:
Regulatory assets	32,178		33,019
GOLDEN STATE WATER COMPANY | Derivative unrealized loss
Regulatory matters:
Regulatory assets	2,625		2,941
GOLDEN STATE WATER COMPANY | Low income rate assistance balancing accounts
Regulatory matters:
Regulatory assets	5,640		5,972
GOLDEN STATE WATER COMPANY | General Rate Case Memorandum Accounts
Regulatory matters:
Regulatory assets	9,264		10,522
GOLDEN STATE WATER COMPANY | Deferred Income Tax Charge
Regulatory matters:
Regulatory assets	(82,680)		(83,231)
GOLDEN STATE WATER COMPANY | Flow-through taxes, net
Regulatory matters:
Regulatory assets	(17,133)		(17,716)
GOLDEN STATE WATER COMPANY | Other Regulatory Assets Net [Member]
Regulatory matters:
Regulatory assets	$ 15,449		$ 14,875