<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Version>2.4.1.9</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ContextCount>436</ContextCount>
  <ElementCount>517</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>118</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>18</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Document and Entity Information Document</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/DocumentAndEntityInformationDocument</Role>
      <ShortName>Document and Entity Information Document</ShortName>
    </Report>
    <Report>
      <IsDefault>true</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1001501 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/ConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002000 - Statement - Consolidated Statements of Income and Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/ConsolidatedStatementsOfIncomeAndComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Income and Comprehensive Income</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1002501 - Statement - Consolidated Statements of Comprehensive Income (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/ConsolidatedStatementsOfComprehensiveIncomeParenthetical</Role>
      <ShortName>Consolidated Statements of Comprehensive Income (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1003000 - Statement - Consolidated Statements of Changes in Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity</Role>
      <ShortName>Consolidated Statements of Changes in Shareholders' Equity</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1003501 - Statement - Consolidated Statements of Changes in Shareholders' Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/ConsolidatedStatementsOfChangesInShareholdersEquityParenthetical</Role>
      <ShortName>Consolidated Statements of Changes in Shareholders' Equity (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1004000 - Statement - Consolidated Statement of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/ConsolidatedStatementOfCashFlows</Role>
      <ShortName>Consolidated Statement of Cash Flows</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2103100 - Disclosure - Capitalization</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/Capitalization</Role>
      <ShortName>Capitalization</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2104100 - Disclosure - Lines of Credit</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/LinesOfCredit</Role>
      <ShortName>Lines of Credit</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2105100 - Disclosure - Long-Term Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/LongTermDebt</Role>
      <ShortName>Long-Term Debt</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2106100 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2107100 - Disclosure - Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IntangibleAssets</Role>
      <ShortName>Intangible Assets</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2108100 - Disclosure - Commitments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/Commitments</Role>
      <ShortName>Commitments</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/Contingencies</Role>
      <ShortName>Contingencies</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Partnership Interest</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/PartnershipInterest</Role>
      <ShortName>Partnership Interest</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2110100 - Disclosure - Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlans</Role>
      <ShortName>Benefit Plans</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2111100 - Disclosure - Equity Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/EquityPlans</Role>
      <ShortName>Equity Plans</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2112100 - Disclosure - Segment and Non-Tariffed Businesses Reporting</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SegmentAndNonTariffedBusinessesReporting</Role>
      <ShortName>Segment and Non-Tariffed Businesses Reporting</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2113100 - Disclosure - California Water Service Group Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/CaliforniaWaterServiceGroupStock</Role>
      <ShortName>California Water Service Group Stock</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2119100 - Disclosure - Unaudited Quarterly Financial Data</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/UnauditedQuarterlyFinancialData</Role>
      <ShortName>Unaudited Quarterly Financial Data</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2120100 - Schedule - Valuation and Qualifying Accounts and Reserves (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.sjwater.com/role/ValuationAndQualifyingAccountsAndReservesNotes</Role>
      <ShortName>Valuation and Qualifying Accounts and Reserves (Notes)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2202201 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2302302 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Long-Term Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/LongTermDebtTables</Role>
      <ShortName>Long-Term Debt (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2306301 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2307301 - Disclosure - Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IntangibleAssetsTables</Role>
      <ShortName>Intangible Assets (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2310301 - Disclosure - Benefit Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansTables</Role>
      <ShortName>Benefit Plans (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2311301 - Disclosure - Equity Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/EquityPlansTables</Role>
      <ShortName>Equity Plans (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2312301 - Disclosure - Segment and Non-Tariffed Businesses Reporting (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SegmentAndNonTariffedBusinessesReportingTables</Role>
      <ShortName>Segment and Non-Tariffed Businesses Reporting (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2319301 - Disclosure - Unaudited Quarterly Financial Data (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/UnauditedQuarterlyFinancialDataTables</Role>
      <ShortName>Unaudited Quarterly Financial Data (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2402403 - Disclosure - Summary of Significant Accounting Policies Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesNarrativeDetails</Role>
      <ShortName>Summary of Significant Accounting Policies Narrative (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2402404 - Disclosure - Summary of Significant Accounting Policies (Utility Plant) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesUtilityPlantDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Utility Plant) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2402405 - Disclosure - Summary of Significant Accounting Policies (Real Estate Investments) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesRealEstateInvestmentsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Real Estate Investments) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2402406 - Disclosure - Summary of Significant Accounting Policies (Regulatory Rate Filings) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesRegulatoryRateFilingsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Regulatory Rate Filings) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2402407 - Disclosure - Summary of Significant Accounting Policies Balancing and Memorandum Accounts (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesBalancingAndMemorandumAccountsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies Balancing and Memorandum Accounts (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2402408 - Disclosure - Summary of Significant Accounting Policies (Revenue, Balancing and Memorandum Accounts) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesRevenueBalancingAndMemorandumAccountsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Revenue, Balancing and Memorandum Accounts) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2402409 - Disclosure - Summary of Significant Accounting Policies (Advances for Construction and Contributions in Aid of Construction) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesAdvancesForConstructionAndContributionsInAidOfConstructionDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Advances for Construction and Contributions in Aid of Construction) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2402410 - Disclosure - Summary of Significant Accounting Policies (Asset Retirement Obligation) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesAssetRetirementObligationDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Asset Retirement Obligation) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2402411 - Disclosure - Summary of Significant Accounting Policies (Earnings per Share) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SummaryOfSignificantAccountingPoliciesEarningsPerShareDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Earnings per Share) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2403401 - Disclosure - Capitalization Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/CapitalizationNarrativeDetails</Role>
      <ShortName>Capitalization Narrative (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2404401 - Disclosure - Lines of Credit Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/LinesOfCreditNarrativeDetails</Role>
      <ShortName>Lines of Credit Narrative (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2405402 - Disclosure - Long-Term Debt Long-term Debt Schedule (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/LongTermDebtLongTermDebtScheduleDetails</Role>
      <ShortName>Long-Term Debt Long-term Debt Schedule (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2405403 - Disclosure - Long-Term Debt Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/LongTermDebtNarrativeDetails</Role>
      <ShortName>Long-Term Debt Narrative (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2405404 - Disclosure - Long-Term Debt Debt Maturity Schedule (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/LongTermDebtDebtMaturityScheduleDetails</Role>
      <ShortName>Long-Term Debt Debt Maturity Schedule (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2406402 - Disclosure - Income Taxes Components of Income Tax Expense (Benefit) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IncomeTaxesComponentsOfIncomeTaxExpenseBenefitDetails</Role>
      <ShortName>Income Taxes Components of Income Tax Expense (Benefit) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2406403 - Disclosure - Income Taxes Federal Statutory Rate Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IncomeTaxesFederalStatutoryRateReconciliationDetails</Role>
      <ShortName>Income Taxes Federal Statutory Rate Reconciliation (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2406404 - Disclosure - Income Taxes Components of Deferred Tax Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IncomeTaxesComponentsOfDeferredTaxAssetsAndLiabilitiesDetails</Role>
      <ShortName>Income Taxes Components of Deferred Tax Assets and Liabilities (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2406405 - Disclosure - Income Taxes Unrecognized Tax Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IncomeTaxesUnrecognizedTaxBenefitsDetails</Role>
      <ShortName>Income Taxes Unrecognized Tax Benefits (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2406406 - Disclosure - Income Taxes Tax Years Under Examination (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IncomeTaxesTaxYearsUnderExaminationDetails</Role>
      <ShortName>Income Taxes Tax Years Under Examination (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2407402 - Disclosure - Intangible Assets Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/IntangibleAssetsNarrativeDetails</Role>
      <ShortName>Intangible Assets Narrative (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2408401 - Disclosure - Commitments Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/CommitmentsNarrativeDetails</Role>
      <ShortName>Commitments Narrative (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2409401 - Disclosure - Partnership Interest Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/PartnershipInterestNarrativeDetails</Role>
      <ShortName>Partnership Interest Narrative (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2410402 - Disclosure - Benefit Plans Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansNarrativeDetails</Role>
      <ShortName>Benefit Plans Narrative (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2410403 - Disclosure - Benefit Plans Actuarial Calculation Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansActuarialCalculationAssumptionsDetails</Role>
      <ShortName>Benefit Plans Actuarial Calculation Assumptions (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2410404 - Disclosure - Benefit Plans Net Periodic Benefit Cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansNetPeriodicBenefitCostDetails</Role>
      <ShortName>Benefit Plans Net Periodic Benefit Cost (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2410405 - Disclosure - Benefit Plans Reconciliation of Funded Status (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansReconciliationOfFundedStatusDetails</Role>
      <ShortName>Benefit Plans Reconciliation of Funded Status (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2410406 - Disclosure - Benefit Plans Amounts Recognized in Balance Sheet (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansAmountsRecognizedInBalanceSheetDetails</Role>
      <ShortName>Benefit Plans Amounts Recognized in Balance Sheet (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2410407 - Disclosure - Benefit Plans Regulatory Asset (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansRegulatoryAssetDetails</Role>
      <ShortName>Benefit Plans Regulatory Asset (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2410408 - Disclosure - Benefit Plans Amortization (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansAmortizationDetails</Role>
      <ShortName>Benefit Plans Amortization (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2410409 - Disclosure - Benefit Plans Plan Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansPlanAssetsDetails</Role>
      <ShortName>Benefit Plans Plan Assets (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2410410 - Disclosure - Benefit Plans Fair Value of Plan Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansFairValueOfPlanAssetsDetails</Role>
      <ShortName>Benefit Plans Fair Value of Plan Assets (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2410411 - Disclosure - Benefit Plans Benefits Expected to be Paid in Next Five Years (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/BenefitPlansBenefitsExpectedToBePaidInNextFiveYearsDetails</Role>
      <ShortName>Benefit Plans Benefits Expected to be Paid in Next Five Years (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2411402 - Disclosure - Equity Plans Equity Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/EquityPlansEquityPlansDetails</Role>
      <ShortName>Equity Plans Equity Plans (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2411403 - Disclosure - Equity Plans Stock Option Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/EquityPlansStockOptionActivityDetails</Role>
      <ShortName>Equity Plans Stock Option Activity (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2411404 - Disclosure - Equity Plans Restricted Stock and Deferred Restricted Stock Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/EquityPlansRestrictedStockAndDeferredRestrictedStockActivityDetails</Role>
      <ShortName>Equity Plans Restricted Stock and Deferred Restricted Stock Activity (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2412402 - Disclosure - Segment and Non-Tariffed Business Reporting (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/SegmentAndNonTariffedBusinessReportingDetails</Role>
      <ShortName>Segment and Non-Tariffed Business Reporting (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2413401 - Disclosure - California Water Service Group Stock Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/CaliforniaWaterServiceGroupStockNarrativeDetails</Role>
      <ShortName>California Water Service Group Stock Narrative (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>2419402 - Disclosure - Unaudited Quarterly Financial Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/UnauditedQuarterlyFinancialInformationDetails</Role>
      <ShortName>Unaudited Quarterly Financial Information (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>2420401 - Schedule - Valuation and Qualifying Accounts and Reserves (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.sjwater.com/role/ValuationAndQualifyingAccountsAndReservesDetails</Role>
      <ShortName>Valuation and Qualifying Accounts and Reserves (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">Columns in Cash Flows statement 'Consolidated Statement of Cash Flows (USD $)' have maximum duration 365 days and at least 43 values. Shorter duration columns must have at least one fourth (10) as many values. Column '1/1/2013 - 3/31/2013' is shorter (89 days) and has only 2 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'Consolidated Statement of Cash Flows (USD $)' have maximum duration 365 days and at least 43 values. Shorter duration columns must have at least one fourth (10) as many values. Column '4/1/2013 - 6/30/2013' is shorter (90 days) and has only 1 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'Consolidated Statement of Cash Flows (USD $)' have maximum duration 365 days and at least 43 values. Shorter duration columns must have at least one fourth (10) as many values. Column '7/1/2013 - 9/30/2013' is shorter (91 days) and has only 1 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'Consolidated Statement of Cash Flows (USD $)' have maximum duration 365 days and at least 43 values. Shorter duration columns must have at least one fourth (10) as many values. Column '10/1/2013 - 12/31/2013' is shorter (91 days) and has only 2 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'Consolidated Statement of Cash Flows (USD $)' have maximum duration 365 days and at least 43 values. Shorter duration columns must have at least one fourth (10) as many values. Column '1/1/2014 - 3/31/2014' is shorter (89 days) and has only 2 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'Consolidated Statement of Cash Flows (USD $)' have maximum duration 365 days and at least 43 values. Shorter duration columns must have at least one fourth (10) as many values. Column '4/1/2014 - 6/30/2014' is shorter (90 days) and has only 1 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'Consolidated Statement of Cash Flows (USD $)' have maximum duration 365 days and at least 43 values. Shorter duration columns must have at least one fourth (10) as many values. Column '7/1/2014 - 9/30/2014' is shorter (91 days) and has only 1 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'Consolidated Statement of Cash Flows (USD $)' have maximum duration 365 days and at least 43 values. Shorter duration columns must have at least one fourth (10) as many values. Column '10/1/2014 - 12/31/2014' is shorter (91 days) and has only 2 values, so it is being removed.</Log>
    <Log type="Info">Columns in Cash Flows statement 'Consolidated Statement of Cash Flows (USD $)' have maximum duration 365 days and at least 43 values. Shorter duration columns must have at least one fourth (10) as many values. Column '6/30/2014 - 6/30/2014' is shorter (0 days) and has only 1 values, so it is being removed.</Log>
    <Log type="Info">'Monetary' elements on report '2402406 - Disclosure - Summary of Significant Accounting Policies (Regulatory Rate Filings) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2405403 - Disclosure - Long-Term Debt Narrative (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2405404 - Disclosure - Long-Term Debt Debt Maturity Schedule (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2410402 - Disclosure - Benefit Plans Narrative (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 1001000 - Statement - Consolidated Balance Sheets</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2011'</Log>
    <Log type="Info">Process Flow-Through: 1001501 - Statement - Consolidated Balance Sheets (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 1002000 - Statement - Consolidated Statements of Income and Comprehensive Income</Log>
    <Log type="Info">	Process Flow-Through: Removing column '0 Months Ended
Jun. 30, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2013'</Log>
    <Log type="Info">Process Flow-Through: 1002501 - Statement - Consolidated Statements of Comprehensive Income (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 1003501 - Statement - Consolidated Statements of Changes in Shareholders' Equity (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 1004000 - Statement - Consolidated Statement of Cash Flows</Log>
  </Logs>
  <InputFiles>
    <File>sjw-20141231.xml</File>
    <File>sjw-20141231.xsd</File>
    <File>sjw-20141231_cal.xml</File>
    <File>sjw-20141231_def.xml</File>
    <File>sjw-20141231_lab.xml</File>
    <File>sjw-20141231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
