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Fair Value Measurement (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt $ 384,802us-gaap_LongTermDebt $ 384,949us-gaap_LongTermDebt
Quoted Prices in Active Markets for Identical Assets    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investment in California Water Service Group 6,352us-gaap_AvailableForSaleSecurities
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6,378us-gaap_AvailableForSaleSecurities
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Significant Observable Inputs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, fair value $ 489,650us-gaap_LongTermDebtFairValue
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$ 460,171us-gaap_LongTermDebtFairValue
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