Revenue from Contract with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 128,414	$ 121,278	$ 245,474	$ 230,355
GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Total operating revenues	91,633	94,753	166,662	177,145
Water Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	88,185	78,717	163,524	149,200
Total operating revenues	91,633	87,074	166,662	158,498
Electric Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax		7,562		17,852
Total operating revenues		7,679		18,647
Electric Service Utility Operations | Bear Valley Electric Service, Inc.
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	8,374
Total operating revenues	8,108
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			20,253
Total operating revenues			19,647
Contracted Services | ASUS
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	28,673	26,525	59,165	53,210
Tariff-based Revenues | Water Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	86,687	77,264	160,975	146,518
Tariff-based Revenues | Electric Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax		7,384		17,416
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	8,330		20,007
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			20,007
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	975	962	1,509	1,696
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		178		436
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	44		246
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			246
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	523	491	1,040	986
Alternative revenues program [Member] | Water Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Alternative revenue program	3,448	(8,357)	(3,138)	(9,298)
Alternative revenues program [Member] | Electric Service Utility Operations | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Alternative revenue program		(117)	606	(795)
Alternative revenues program [Member] | Electric Service Utility Operations | Bear Valley Electric Service, Inc.
Disaggregation of Revenue [Line Items]
Alternative revenue program	(266)
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			606
Water | Contracted Services | ASUS
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	18,765	13,472	37,648	28,173
Wastewater | Contracted Services | ASUS
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	$ 9,908	$ 13,053	$ 21,517	$ 25,037