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Revenue from Contract with Customer - Contract Assets and Contract Liabilities (Details) - American States Utility Services - USD ($)
$ in Thousands
 9 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]    
Receivable from the U.S. government $ 54,968 $ 40,150
Contract assets 19,043 30,388
Contract liabilities $ 8,942 $ 3,911
Minimum    
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]    
Performance obligation fulfillment period 36 years  
Maximum    
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]    
Performance obligation fulfillment period 50 years  
Contracted Services    
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]    
Period of fixed price contracts to operate and maintain the water and/or wastewater systems at various military bases 50 years