Revenue from Contract with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 133,688	$ 134,496	$ 364,043	$ 360,876
GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Total operating revenues	98,701	107,245	275,846	278,145
Water Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	98,822	91,505	248,022	229,930
Total operating revenues	98,701	95,249	257,199	248,112
Electric Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax		9,780		28,841
Total operating revenues		11,996		30,033
Electric Service Utility Operations | Bear Valley Electric Service, Inc.
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	8,719
Total operating revenues	8,288
Electric Service Utility Operations | Golden State Water Company and Bear Valley Electric Service Inc.
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax			26,572
Total operating revenues			26,935
Contracted Services | ASUS
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	26,699	27,251	79,909	82,731
Tariff-based Revenues | Water Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	97,036	89,050	243,553	225,501
Tariff-based Revenues | Electric Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax		9,729		28,693
Tariff-based Revenues | Electric Service Utility Operations | Bear Valley Electric Service, Inc.
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	8,531
Tariff-based Revenues | Electric Service Utility Operations | Golden State Water Company and Bear Valley Electric Service Inc.
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax			25,948
Surcharges (Cost-recovery Activities) | Water Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	1,217	1,900	2,913	2,954
Surcharges (Cost-recovery Activities) | Electric Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax		51		148
Surcharges (Cost-recovery Activities) | Electric Service Utility Operations | Bear Valley Electric Service, Inc.
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	188
Surcharges (Cost-recovery Activities) | Electric Service Utility Operations | Golden State Water Company and Bear Valley Electric Service Inc.
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax			624
Other Products and Services | Water Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	569	555	1,556	1,475
Alternative revenues program [Member] | Water Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Alternative revenue program	(121)	(3,744)	(9,177)	(18,182)
Alternative revenues program [Member] | Electric Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Alternative revenue program		(2,216)		(1,192)
Alternative revenues program [Member] | Electric Service Utility Operations | Bear Valley Electric Service, Inc.
Disaggregation of Revenue [Line Items]
Alternative revenue program	(431)
Alternative revenues program [Member] | Electric Service Utility Operations | Golden State Water Company and Bear Valley Electric Service Inc.
Disaggregation of Revenue [Line Items]
Alternative revenue program			(363)
Water | Contracted Services | ASUS
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	17,143	13,797	45,316	41,772
Wastewater | Contracted Services | ASUS
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	$ 9,556	$ 13,454	$ 34,593	$ 40,959