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Revenue from Contract with Customer (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Disaggregation of Revenue [Line Items]        
Contract liability revenue recognized $ 3.4   $ 3.7  
Performance obligation remaining 0.0   $ 0.0  
Registration payment arrangement period     20 days  
Golden State Water Company        
Disaggregation of Revenue [Line Items]        
Reimbursement Revenue $ 1.0 $ 1.0 $ 2.8 $ 2.8
Contracted Services | American States Utility Services        
Disaggregation of Revenue [Line Items]        
Period of fixed price contracts to operate and maintain the water and/or wastewater systems at various military bases     50 years  
Sales | Water Service Utility Operations | Golden State Water Company        
Disaggregation of Revenue [Line Items]        
Percentage of concentration risk     90.00%  
Sales | Electric Service Utility Operations | Golden State Water Company        
Disaggregation of Revenue [Line Items]        
Percentage of concentration risk     90.00%  
Minimum | American States Utility Services        
Disaggregation of Revenue [Line Items]        
Performance obligation fulfillment period     36 years  
Maximum | American States Utility Services        
Disaggregation of Revenue [Line Items]        
Performance obligation fulfillment period     50 years