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General - Additional Information (Details) (USD $)
In Thousands, unless otherwise specified
 0 Months Ended 12 Months Ended 9 Months Ended
Apr. 01, 2015
Mar. 27, 2015
Dec. 31, 2014
Dec. 31, 2015
Mar. 26, 2015
Jan. 05, 2015
Regulatory Liabilities [Line Items]            
Water reduction target goal (percent)     20.00%sjw_WaterReductionTargetGoalPercentage      
Mandatory Water Reduction, Percentage 25.00%sjw_MandatoryWaterReductionPercentage          
Authorized Regulatory Surcharge, Gross   $ 1,876sjw_AuthorizedRegulatorySurchargeGross        
Memorandum Account, Recovery Request         $ 9,567sjw_MemorandumAccountRecoveryRequest $ 976sjw_MemorandumAccountRecoveryRequest
Scenario, Forecast [Member]            
Regulatory Liabilities [Line Items]            
Water reduction target goal (percent)       30.00%sjw_WaterReductionTargetGoalPercentage
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember