Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 182,716	$ 161,782	$ 493,795	$ 452,361
GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Total operating revenues	132,323	124,043	354,023	324,732
Water: | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	132,961	121,356	354,393	304,791
Total operating revenues	132,323	124,043	354,023	324,732
Electric: | BVES
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	12,984	8,919	39,924	30,561
Total operating revenues	13,332	9,040	41,262	29,948
Contracted services: | ASUS
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	37,061	28,699	98,510	97,681
Tariff-based revenues | Water: | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	130,229	119,716	347,800	300,442
Tariff-based revenues | Electric: | BVES
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	11,823	8,892	37,336	30,431
CPUC-approved surcharges (cost-recovery activities) | Water: | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	2,052	946	4,613	2,405
CPUC-approved surcharges (cost-recovery activities) | Electric: | BVES
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	1,161	27	2,588	130
Other | Water: | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	680	694	1,980	1,944
Alternative revenues program | Water: | GOLDEN STATE WATER COMPANY
Disaggregation of Revenue [Line Items]
Alternative revenue programs, net	(638)	2,687	(370)	19,941
Alternative revenues program | Electric: | BVES
Disaggregation of Revenue [Line Items]
Alternative revenue programs, net	348	121	1,338	(613)
Water | Contracted services: | ASUS
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	20,992	14,651	52,002	57,821
Wastewater | Contracted services: | ASUS
Disaggregation of Revenue [Line Items]
Revenue from contract with customer, excluding assessed tax	$ 16,069	$ 14,048	$ 46,508	$ 39,860