Summary of Significant Accounting Policies (Details) customer in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) customer registrant	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Oct. 27, 2015 USD ($)
Summary of significant accounting policies
Deferred Finance Costs, Net	$ 4,271,000	$ 4,641,000
Related Party Transaction, Amounts of Transaction	$ 3,900,000	2,600,000	$ 2,700,000
Basis of Presentation:
Number of registrants filing combined report | registrant	2
Impairment of Long-Lived Assets
Impairment of long-lived assets	$ 0	0	0
Goodwill
Goodwill arose from acquisition of subcontractor's business	1,100,000	1,100,000
Sales and Use Taxes:
Non-income tax assessments accounted on a gross basis	$ 16,801,000	16,636,000	$ 16,722,000
Military Utility Privatization Subsidiaries
Summary of significant accounting policies
Period of Fixed Price Contracts to Maintain Water Systems at Various Military Bases	50 years
GSWC
Summary of significant accounting policies
Deferred Finance Costs, Net	$ 4,271,000	$ 4,641,000
Property and Depreciation
Aggregate composite rate for depreciation (as a percent)	2.90%	3.20%	3.20%
Depreciation on transportation equipment	$ 259,000	$ 641,000	$ 678,000
Estimated useful lives of utility plant, as authorized by the CPUC
Generation	40 years
Interest
Amount recorded in AFUDC	$ 101,000	694,000	24,000
Alternative-Revenue Programs
Number of months within which expected additional revenue collection is recorded	24 months
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	$ 423,124,000
Sales and Use Taxes:
Franchise fees billed to customers and recorded as operating revenue	3,500,000	3,800,000	3,700,000
Non-income tax assessments accounted on a gross basis	15,444,000	15,244,000	15,221,000
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	325,582,000	325,853,000
GSWC | Fair Value
Fair Value of Financial Instruments
Long-term debt-GSWC		403,844,000
GSWC | Fair Value | Level 2
Fair Value of Financial Instruments
Long-term debt-GSWC	$ 423,124,000
GSWC | Minimum [Member]
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 [Member]
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
GSWC | Notes Payable, Other Payables [Member]
Related Party Transactions
Debt Instrument, Face Amount						$ 40,000,000
Debt Instrument, Maximum Borrowing Capacity						40,000,000
GSWC | Purchase, production, distribution and sale of water
Nature of Operations:
Number of customers served | customer	261
Interest
Weighted cost of capital (as a percent)	8.34%
GSWC | Electric
Nature of Operations:
Number of customers served | customer	24
Sales and Use Taxes:
Cost Of Debt Percent	6.96%
American States Utility Services [Member]
Sales and Use Taxes:
Non-income tax assessments accounted on a gross basis	$ 309,000	367,000	$ 490,000
American States Utility Services [Member] | Notes Payable, Other Payables [Member]
Related Party Transactions
Debt Instrument, Face Amount						10,000,000
Debt Instrument, Maximum Borrowing Capacity						$ 10,000,000
American States Utility Services [Member] | Military Utility Privatization Subsidiaries
Nature of Operations:
Period of fixed price contracts to operate and maintain the water and/or wastewater systems at various military bases	50 years
AWR
Related Party Transactions
Maximum borrowing capacity on line of credit				$ 150,000,000	$ 100,000,000.0
Notes Receivable | GSWC | Notes Payable, Other Payables [Member]
Related Party Transactions
Notes Receivable, Related Parties, Current	$ 0
Notes Receivable | AWR | Notes Payable, Other Payables [Member]
Related Party Transactions
Notes Receivable, Related Parties, Current		$ 0			$ 0
Sales [Member] | GSWC | Purchase, production, distribution and sale of water
Nature of Operations:
Percentage of total revenues	90.00%	90.00%	90.00%
Syndicated revolving credit facility | AWR | Syndicated revolving credit facility
Related Party Transactions
Maximum borrowing capacity on line of credit	$ 150,000,000