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Revenues (Details) - USD ($)
$ in Millions
1 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disaggregation of Revenue [Line Items]          
Revenue, Performance Obligation, Payment Terms     20 days    
Golden State Water Company [Member]          
Disaggregation of Revenue [Line Items]          
Cost of Reimbursable Expense     $ 3.6 $ 3.6 $ 3.5
Period within which Expected Additional Revenue Collection is Recorded Subject to Undercollection of Revenue     24 months    
Contracted Services [Member] | American States Utility Services [Member]          
Disaggregation of Revenue [Line Items]          
Period of Fixed Price Contracts to Operate and Maintain Water Systems at Various Military Bases 50 years   50 years    
Sales [Member] | Water Service Utility Operations [Member] | Golden State Water Company [Member]          
Disaggregation of Revenue [Line Items]          
Percentage of total revenues     90.00% 90.00% 90.00%
Sales [Member] | Electric Service Utility Operations [Member] | Golden State Water Company [Member]          
Disaggregation of Revenue [Line Items]          
Percentage of total revenues   90.00%