Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) customer registrant	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 14, 2022 USD ($)	Feb. 02, 2022 USD ($)	Jan. 26, 2022 USD ($)	Jul. 12, 2021 USD ($)
Nature of Operations:
Number of customers served | customer	1,000,000
Number of States in which Entity Operates	9
Number of registrants filing combined report | registrant	2
Related Party Transactions
Related Party Transaction, Amounts of Transaction	$ 5,200,000	$ 5,300,000	$ 4,900,000
Impairment of Long-Lived Assets
Asset Retirement Obligation, Legally Restricted Assets, Fair Value	0
Impairment of long-lived assets	0	0	$ 0
Goodwill
Goodwill arose from acquisition of subcontractor's business	$ 1,100,000	1,100,000
Advances for Construction and Contributions in aid of Constructions
Period for refund of advances for construction	40 years
Fair Value of Financial Instruments
Long-term debt-GSWC	$ 424,151,000
Total	(25,454,000)	(22,796,000)
Level 1
Fair Value of Financial Instruments
Long-term debt-GSWC	0
Level 3
Fair Value of Financial Instruments
Long-term debt-GSWC	0
Carrying Amount
Fair Value of Financial Instruments
Long-term debt-GSWC	450,373,000
Fair Value | Level 2
Fair Value of Financial Instruments
Long-term debt-GSWC	424,151,000
GSWC
Related Party Transactions
Intercompany note payable	$ 129,000,000	$ 49,280,000
Intercompany borrowings payment term	24 months
Property and Depreciation
Aggregate composite rate for depreciation (as a percent)	2.20%	2.20%	2.20%
Depreciation	$ 37,300,000	$ 35,500,000	$ 32,900,000
Depreciation on transportation equipment	$ 382,000	379,000	353,000
Estimated useful lives of utility plant, as authorized by the CPUC
Generation	40 years
Fair Value of Financial Instruments
Long-term debt-GSWC	$ 391,198,000
Water Utility Relief Funding For Overdue Water Bills Per Budget Act Of 2021							$ 1,000,000,000
Relief funding	9,500,000
Total	(26,574,000)	(24,082,000)
Regulatory Asset CEMA	3,500,000
GSWC | COVID-19 memorandum account
Fair Value of Financial Instruments
Total	3,478,000	1,663,000
GSWC | Level 1
Fair Value of Financial Instruments
Long-term debt-GSWC	0
GSWC | Level 3
Fair Value of Financial Instruments
Long-term debt-GSWC	0
GSWC | Carrying Amount
Fair Value of Financial Instruments
Long-term debt-GSWC	415,373,000	415,788,000
GSWC | Fair Value
Fair Value of Financial Instruments
Long-term debt-GSWC		490,852,000
GSWC | Fair Value | Level 2
Fair Value of Financial Instruments
Long-term debt-GSWC	$ 391,198,000
GSWC | Minimum
Estimated useful lives of utility plant, as authorized by the CPUC
Source of water supply	30 years
Pumping	25 years
Water treatment	20 years
Transmission and Distribution	25 years
Other plant	7 years
GSWC | Maximum
Estimated useful lives of utility plant, as authorized by the CPUC
Source of water supply	50 years
Pumping	40 years
Water treatment	35 years
Transmission and Distribution	55 years
Other plant	40 years
BVESI
Related Party Transactions
Related Party Transaction, Amounts of Transaction	$ 2,700,000	2,800,000	1,300,000
Interest
Public Utilities, Allowance for Funds Used During Construction, Additions	$ 106,000	$ 216,000	$ 200,000
Fair Value of Financial Instruments
Relief funding				$ 152,000	$ 321,000	$ 9,500,000
Annual basis residential disconnections cap	2.50%
Regulatory Asset CEMA	$ 497,000
Water: | GSWC
Nature of Operations:
Number of customers served | customer	263,000
Electric: | BVESI
Nature of Operations:
Number of customers served | customer	24,700
Contracted services: | American States Utility Services
Nature of Operations:
Period of fixed price contracts to operate and maintain the water and/or wastewater systems at various military bases	50 years