Regulatory Matters: (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Regulatory matters:
Regulatory asset not accruing carrying costs	$ 59,400			$ 59,400
Other Liabilities, Current	$ 13,262			$ 13,262		$ 15,109
Cost of Capital, Proceeding for Water Regions [Member]
Regulatory matters:
Return on Equity Percentage	9.40%			9.40%
Weighted Cost of Capital Percent	8.30%			8.30%
Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account
Regulatory matters:
Increase (Decrease) in Other Regulatory Assets				$ 9,900
Pension and other post-retirement obligations
Regulatory matters:
Regulatory asset not accruing carrying costs	$ 33,900			33,900
Derivative unrealized loss
Regulatory matters:
Regulatory asset not accruing carrying costs	1,710			1,710
Revenue Subject to Refund [Member]
Regulatory matters:
Decrease in revenues requirement to reflect the newly adopted Cost of Capital for GSWC				952
GOLDEN STATE WATER COMPANY
Regulatory matters:
Regulatory assets	(10,799)			(10,799)		2,042
Other Liabilities, Current	12,383			12,383		14,705
GOLDEN STATE WATER COMPANY | Modified Cost Balancing Account [Member]
Regulatory matters:
Regulatory assets	$ 23,000			$ 23,000
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	7.90%			7.90%
GOLDEN STATE WATER COMPANY | Revenue Subject to Refund [Member]
Regulatory matters:
Adjustments recorded to revalue deferred taxes as a result of the tax cut and job act of 2017 impact	$ 3,700			$ 6,400
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account
Regulatory matters:
Investment Term				90 days
Regulatory Asset Amount Billed to Customers as Surcharges	5,600		$ 9,500	$ 9,800	$ 13,400
Regulatory assets	29,604			29,604		29,556
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism [Member]
Regulatory matters:
Regulatory assets	6,600			6,600
GOLDEN STATE WATER COMPANY | Costs deferred for future recovery on Aerojet case
Regulatory matters:
Regulatory assets	10,272			10,272		10,656
GOLDEN STATE WATER COMPANY | Pension and other post-retirement obligations
Regulatory matters:
Regulatory assets	31,705			31,705		33,019
GOLDEN STATE WATER COMPANY | Derivative unrealized loss
Regulatory matters:
Regulatory assets						2,941
GOLDEN STATE WATER COMPANY | Flow-through taxes, net
Regulatory matters:
Regulatory assets	(16,508)			(16,508)		(17,716)
GOLDEN STATE WATER COMPANY | Low income rate assistance balancing accounts
Regulatory matters:
Regulatory assets	4,982			4,982		5,972
GOLDEN STATE WATER COMPANY | General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Regulatory assets	8,241			8,241		10,522
GOLDEN STATE WATER COMPANY | Deferred Income Tax Charge [Member]
Regulatory matters:
Regulatory assets	82,128			82,128		(83,231)
GOLDEN STATE WATER COMPANY | Other regulatory assets
Regulatory matters:
Regulatory assets	15,677			15,677		14,875
GOLDEN STATE WATER COMPANY | Revenue Subject to Refund [Member]
Regulatory matters:
Regulatory assets	(14,354)			(14,354)		$ (4,552)
Decrease in revenues requirement to reflect the newly adopted Cost of Capital for GSWC				3,600
Electric Service Utility Operations [Member] | Revenue Subject to Refund [Member]
Regulatory matters:
Adjustments recorded to revalue deferred taxes as a result of the tax cut and job act of 2017 impact	$ 356			$ 723
Maximum | GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account
Regulatory matters:
Regulatory Asset Recovery Periods		24 months
Recovery Period for under Collection, Balances Greater than 15 Percent of Adopted Annual Revenues				24 years
Minimum [Member] | GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account
Regulatory matters:
Recovery Period for under Collection, Balances Greater than 15 Percent of Adopted Annual Revenues				12 months