XML 74 R57.htm IDEA: XBRL DOCUMENT v3.8.0.1

Benefit Plans Narrative (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) yr	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Pension Plans [Abstract]
Number of compensation years included in benefit calculation | yr	3
Expected future working lifetime of participants	12 years 9 months 26 days
Market gains (losses)	$ 200,000	$ 898,000
Return on investments for past 10 years, percent	6.07%
Investments benchmark for past 10 years, percent	6.34%
Return on investments for past five years, percent	8.55%
Investments benchmark for past five years, percent	9.22%
Flexible Spending Plan [Abstract]
Annual maximum contribution limit under Health Care Spending Account plan	$ 2,500.0
Annual maximum contribution limit under Dependent Care Spending Account plan	5,000
Deferral Plan [Abstract]
Employer contributions to deferral plan	$ 1,585,000	1,242,000	$ 1,149,000
Fixed Income Funds [Member]
Pension Plans [Abstract]
Target plan asset allocations	25.00%
Bonds [Member]
Pension Plans [Abstract]
Actual plan asset allocations	32.00%
Cash and Cash Equivalents [Member]
Pension Plans [Abstract]
Actual plan asset allocations	6.00%
Equity Securities [Member]
Pension Plans [Abstract]
Actual plan asset allocations	62.00%
Private Corporation Assets [Member]
Pension Plans [Abstract]
Target plan asset allocations	5.00%
Minimum [Member]
Pension Plans [Abstract]
Period for performance standards	3 years
Maximum [Member]
Pension Plans [Abstract]
Period for performance standards	5 years
Executive Supplemental Retirement Plan [Member]
Pension Plans [Abstract]
Projected benefit obligation	$ 24,832,000	19,051,000
Net periodic pension cost	2,186,000	1,729,000	1,542,000
Executives and Non-employee Directors [Member] | Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits [Member]
Special Deferral Election Plan and Deferral Election Program [Abstract]
Deferrals by executives and non-employee directors	$ 4,528,000	$ 4,250,000	$ 4,073,000

X

- Definition

Deferral Plan [Abstract]

+ References

No definition available.

+ Details

Name:	sjw_DeferralPlanAbstract
Namespace Prefix:	sjw_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Deferred Compensation Arrangement With Individual, Deferral Amount

+ References

No definition available.

+ Details

Name:	sjw_DeferredCompensationArrangementWithIndividualDeferralAmount
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Number of Compensation Years

+ References

No definition available.

+ Details

Name:	sjw_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationNumberOfCompensationYears
Namespace Prefix:	sjw_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Defined Benefit Plan, Period for Performance Standards

+ References

No definition available.

+ Details

Name:	sjw_DefinedBenefitPlanPeriodForPerformanceStandards
Namespace Prefix:	sjw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Defined Benefit Plan, Return on Investments Past 10 Years, Benchmark Percent

+ References

No definition available.

+ Details

Name:	sjw_DefinedBenefitPlanReturnonInvestmentsPast10YearsBenchmarkPercentnt
Namespace Prefix:	sjw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Defined Benefit Plan, Return on Investments Past 10 Years, Percent

+ References

No definition available.

+ Details

Name:	sjw_DefinedBenefitPlanReturnonInvestmentsPast10YearsPercent
Namespace Prefix:	sjw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Defined Benefit Plan, Return on Investments Past 5 Years, Benchmark Percent

+ References

No definition available.

+ Details

Name:	sjw_DefinedBenefitPlanReturnonInvestmentsPast5YearsBenchmarkPercent
Namespace Prefix:	sjw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Defined Benefit Plan, Unamortized Actuarial Gains (Losses), Expected Working Lifetime of Participants

+ References

No definition available.

+ Details

Name:	sjw_DefinedBenefitPlanUnamortizedActuarialGainsLossesExpectedWorkingLifetimeOfParticipants
Namespace Prefix:	sjw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Defined Benfit Plan, Return on Investments Past 5 Years, Percent

+ References

No definition available.

+ Details

Name:	sjw_DefinedBenfitPlanReturnonInvestmentsPast5YearsPercent
Namespace Prefix:	sjw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Dependent Care Spending Account, Annual Maximum Employee Contribution

+ References

No definition available.

+ Details

Name:	sjw_DependentCareSpendingAccountAnnualMaximumEmployeeContribution
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Flexible Spending Plan [Abstract]

+ References

No definition available.

+ Details

Name:	sjw_FlexibleSpendingPlanAbstract
Namespace Prefix:	sjw_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Health Care Spending Account, Annual Maximum Employee Contribution

+ References

No definition available.

+ Details

Name:	sjw_HealthCareSpendingAccountAnnualMaximumEmployeeContribution
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Pension Plans [Abstract]

+ References

No definition available.

+ Details

Name:	sjw_PensionPlansAbstract
Namespace Prefix:	sjw_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Special Deferral Election Plan and Deferral Election Program [Abstract]

+ References

No definition available.

+ Details

Name:	sjw_SpecialDeferralElectionPlanAndDeferralElectionProgramAbstract
Namespace Prefix:	sjw_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of contributions made by employer into fund established for purposes of making future disbursement to individual in accordance with deferred compensation arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(4)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amount of net periodic benefit cost (credit) for defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_BondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=sjw_PrivateCorporationAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_TitleOfIndividualAxis=sjw_ExecutivesAndNonEmployeeDirectorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis=us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: