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Equity Plans Equity Plans (Details) (USD $) In Thousands, except Share data, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 purchase_interval | Dec. 31, 2013 | Dec. 31, 2012
Summary of Activity under the Plan [Abstract] |  |  |
Compensation costs charged to income | $ 1,031us-gaap_AllocatedShareBasedCompensationExpense | $ 912us-gaap_AllocatedShareBasedCompensationExpense | $ 564us-gaap_AllocatedShareBasedCompensationExpense
Proceeds from the exercise of stock options and similar instruments | 1,917us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions | 1,004us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions | 989us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions
Tax benefits realized from share options exercised | 462us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities | 28us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities | 97us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities
Employee Stock Purchase Plan [Abstract] |  |  |
Number of purchases intervals under the plan since inception | 17sjw_EmployeeStockPurchasePlanNumberOfPurchasesSinceInception |  |
Shares issued during the period under the plan | 35,682us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans | 30,869us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans | 29,468us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans
Cash received from employees toward purchases under the plan | 854sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEmployeeContributionsToEmployeeStockPurchasePlan | 796sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEmployeeContributionsToEmployeeStockPurchasePlan | 627sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardEmployeeContributionsToEmployeeStockPurchasePlan
Restricted Stock and Deferred Restricted Stock [Member] |  |  |
Summary of Activity under the Plan [Abstract] |  |  |
Compensation costs charged to income | 883us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember | 784us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember | 460us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember
Tax benefits realized from share options exercised | 249us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember | 97us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember | 36us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember
Employee Stock Purchase Plan [Abstract] |  |  |
Unrecognized compensation cost | 1,606us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |
Deferred Restricted Stock Awards [Member] |  |  |
Dividend Equivalent Rights [Abstract] |  |  |
Cumulative dividend equivalent rights converted to deferred restricted stock awards | 66,458sjw_CumulativeDividendEquivalentRightsConvertedToDeferredRestrictedStockAwards / us-gaap_AwardTypeAxis = sjw_DeferredRestrictedStockAwardsMember | 61,733sjw_CumulativeDividendEquivalentRightsConvertedToDeferredRestrictedStockAwards / us-gaap_AwardTypeAxis = sjw_DeferredRestrictedStockAwardsMember | 56,349sjw_CumulativeDividendEquivalentRightsConvertedToDeferredRestrictedStockAwards / us-gaap_AwardTypeAxis = sjw_DeferredRestrictedStockAwardsMember
Employee Stock Option [Member] |  |  |
Summary of Activity under the Plan [Abstract] |  |  |
Proceeds from the exercise of stock options and similar instruments | 1,044us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 198us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 318us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember
Tax benefits realized from share options exercised | 213us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | (69)us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 61us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember
Dividend Equivalent Rights [Member] |  |  |
Dividend Equivalent Rights [Abstract] |  |  |
Liability for dividend equivalent rights | 122sjw_LiabilityForDividendEquivalentRightsPeriodIncreaseDecrease / us-gaap_AwardTypeAxis = sjw_DividendEquivalentRightsMember | 128sjw_LiabilityForDividendEquivalentRightsPeriodIncreaseDecrease / us-gaap_AwardTypeAxis = sjw_DividendEquivalentRightsMember | 128sjw_LiabilityForDividendEquivalentRightsPeriodIncreaseDecrease / us-gaap_AwardTypeAxis = sjw_DividendEquivalentRightsMember
Incentive Plan [Member] |  |  |
Option Indexed to Issuer's Equity [Line Items] |  |  |
Number of shares reserved for issuance under the plan | 1,800,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = sjw_IncentivePlanMember |  |
Maximum number of shares per employee | 600,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee / us-gaap_PlanNameAxis = sjw_IncentivePlanMember |  |
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued Pursuant To The Plan | 429,352sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPursuantToPlan / us-gaap_PlanNameAxis = sjw_IncentivePlanMember | 341,914sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPursuantToPlan / us-gaap_PlanNameAxis = sjw_IncentivePlanMember | 287,534sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPursuantToPlan / us-gaap_PlanNameAxis = sjw_IncentivePlanMember
Shares issuable under the plan upon exercise of outstanding awards | 296,831sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuableUponExercise / us-gaap_PlanNameAxis = sjw_IncentivePlanMember | 307,919sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuableUponExercise / us-gaap_PlanNameAxis = sjw_IncentivePlanMember | 327,093sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuableUponExercise / us-gaap_PlanNameAxis = sjw_IncentivePlanMember
Number of shares available for grant | 1,073,817us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = sjw_IncentivePlanMember |  |
Dividend Reinvestment and Stock Purchase Plan [Member] |  |  |
Option Indexed to Issuer's Equity [Line Items] |  |  |
Number of shares reserved for issuance under the plan | 3,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember |  |
Shares issued under the plan | 829sjw_StockIssuedDuringPeriodSharesDividendReinvestmentAndStockPurchasePlan / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember | 3,487sjw_StockIssuedDuringPeriodSharesDividendReinvestmentAndStockPurchasePlan / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember | 1,679sjw_StockIssuedDuringPeriodSharesDividendReinvestmentAndStockPurchasePlan / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember
Summary of Activity under the Plan [Abstract] |  |  |
Proceeds from the exercise of stock options and similar instruments | 34us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember | 84us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember | 83us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember
Employee Stock [Member] |  |  |
Summary of Activity under the Plan [Abstract] |  |  |
Compensation costs charged to income | 148us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember | 128us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember | 104us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember
Proceeds from the exercise of stock options and similar instruments | 839us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember | 722us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember | 588us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember
Employee Stock Purchase Plan [Abstract] |  |  |
Purchase price of common stock to employees under the plan, percent | 85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember |  |
Maximum amount of base salary employees can designate for share purchase under the plan | 10.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember |  |
Expenses recorded under the plan | 151us-gaap_StockOptionPlanExpense / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember | 140us-gaap_StockOptionPlanExpense / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember | 110us-gaap_StockOptionPlanExpense / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember
Unrecognized compensation cost | $ 68us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember |  |

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- Definition Number of shares reserved for issuance under equity instrument agreements awarded that validly exist and are outstanding, including vested instruments. + References No definition available. + Details
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- Definition Cumulative number of shares issued pursuant to the Plan. + References No definition available. + Details
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- Definition Number of shares issued during the period from a dividend reinvestment and stock purchase plan (DRSPP). A dividend reinvestment and stock purchase plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity and to purchase additional shares. + References No definition available. + Details
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Amount of cash inflow from realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 20 -Section 55 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=32706628&loc=d3e11374-113907 + Details
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- Definition The total cash inflow associated with the amount received from holders to acquire the entity's shares under incentive and share awards, including stock option exercises. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 + Details
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- Definition The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The highest quantity of shares an employee can purchase under the plan per period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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