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Fair Value Measurement (Details) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt $ 433,515 $ 433,460
Significant Observable Inputs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, fair value 506,455 502,446
Quoted Prices in Active Markets for Identical Assets    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investment in California Water Service Group $ 3,585 $ 3,390