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Summary of Significant Accounting Policies (Revenue, Balancing and Memorandum Accounts) (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Revenue from External Customer [Line Items]      
Regulated operating revenue, water surcharge $ 3,872sjw_RegulatedOperatingRevenueWaterSurcharge $ 3,741sjw_RegulatedOperatingRevenueWaterSurcharge $ 3,862sjw_RegulatedOperatingRevenueWaterSurcharge
San Jose Water Company [Member]      
Revenue from External Customer [Line Items]      
Nonregulated operating revenue $ 6,175us-gaap_UnregulatedOperatingRevenue
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 $ 5,882us-gaap_UnregulatedOperatingRevenue
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 $ 5,523us-gaap_UnregulatedOperatingRevenue
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember