Number of persons employed by the Entity

No definition available.

Name:	dei_EntityNumberOfEmployees
Namespace Prefix:	dei_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Bargaining Agreements, Term

+ References

No definition available.

+ Details

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

- Definition

Collective Bargaining Agreement, Wage Increase, Percent, Year One

+ References

No definition available.

+ Details

Name:	sjw_CollectiveBargainingAgreementWageIncreasePercentYearOne
Namespace Prefix:	sjw_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Collective Bargaining Agreement, Wage Increase, Percent, Year Three

+ References

No definition available.

+ Details

Name:	sjw_CollectiveBargainingAgreementWageIncreasePercentYearThree
Namespace Prefix:	sjw_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Collective Bargaining Agreement, Wage Increase, Percent, Year Two

+ References

No definition available.

+ Details

Name:	sjw_CollectiveBargainingAgreementWageIncreasePercentYearTwo
Namespace Prefix:	sjw_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contract Agreement, Term

+ References

No definition available.

+ Details

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

- Definition

Increase in Delivery Schedule, Percent

+ References

No definition available.

+ Details

Name:	sjw_IncreaseInDeliverySchedulePercent
Namespace Prefix:	sjw_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Long-term Purchase Commitment, Minimum Acre Feet Required

+ References

No definition available.

+ Details

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

- Definition

Long-term Purchase Commitment, Minimum Percentage Required, Next Twelve Months

+ References

No definition available.

+ Details

Name:	sjw_LongTermPurchaseCommitmentMinimumPercentageRequiredNextTwelveMonths
Namespace Prefix:	sjw_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Long-term Purchase Commitment, Minimum Volume Required, Next Twelve Months

+ References

No definition available.

+ Details

Name:	sjw_LongTermPurchaseCommitmentMinimumVolumeRequiredNextTwelveMonths
Namespace Prefix:	sjw_
Data Type:	dtr-types:volumeItemType
Balance Type:	na
Period Type:	instant

- Definition

Long-term Purchase Commitment, Wholesale Discount

+ References

No definition available.

+ Details

Name:	sjw_LongTermPurchaseCommitmentWholesaleDiscount
Namespace Prefix:	sjw_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Definition

Long-term Purchase Commitment, Fixed Price

+ References

No definition available.

+ Details

Name:	sjw_LongtermPurchaseCommitmentFixedPrice
Namespace Prefix:	sjw_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Definition

Long-term Purchase Commitment, Tariff Rate

+ References

No definition available.

+ Details

Name:	sjw_LongtermPurchaseCommitmentTariffRate
Namespace Prefix:	sjw_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Long-term Purchase Commitment, Water Purchased

+ References

No definition available.

+ Details

Name:	sjw_LongtermPurchaseCommitmentWaterPurchased
Namespace Prefix:	sjw_
Data Type:	dtr-types:volumeItemType
Balance Type:	na
Period Type:	duration

- Definition

Master Contract, Negotiated Term for Delivery Schedules

+ References

No definition available.

+ Details

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

- Definition

Notice Period Required for Contract Adjustment

+ References

No definition available.

+ Details

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

- Definition

Purchased Water, Gallons

+ References

No definition available.

+ Details

Name:	sjw_PurchasedWaterGallons
Namespace Prefix:	sjw_
Data Type:	dtr-types:volumeItemType
Balance Type:	na
Period Type:	duration

- Definition

Reduction in Delivery Schedule, Percent

+ References

No definition available.

+ Details

Name:	sjw_ReductioninDeliverySchedulePercent
Namespace Prefix:	sjw_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Cost of water purchased, may include any water related assessment. If water is bought on a unit volume basis, would also be considered as commodity costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2)
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

+ Details

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

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 928
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6473545&loc=d3e61844-108004

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseRenewalTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermPurchaseCommitmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period covered by the long-term purchase commitment, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_LongtermPurchaseCommitmentPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of purchase arrangement to be paid in next fiscal year following current fiscal year. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitment, and short-term purchase commitment. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

No definition available.

+ Details

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

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=sjw_UnionMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=sjw_SouthCentralConnecticutRegionalWaterAuthorityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=sjw_CapacityAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=sjw_TheMetropolitanDistrictMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=sjw_KennebecWaterDistrictMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=sjw_InternationalUnionOfOperatingEngineersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_ServiceAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=sjw_ConcessionFeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseContractualTermAxis=sjw_LeaseTermOptionOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseContractualTermAxis=sjw_LeaseTermOptionTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseContractualTermAxis=sjw_LeaseTermOptionThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sjw_MajorSupplierAxis=sjw_SantaClaraValleyWaterDistrictMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sjw_MajorSupplierAxis=sjw_GuadalupeBlancoRiverAuthorityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sjw_SubsidiaryOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sjw_MajorSupplierAxis=sjw_LowerColoradoRiverAuthorityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments (Details) $ / yr in Thousands, $ in Thousands							12 Months Ended
Commitments (Details) $ / yr in Thousands, $ in Thousands	Feb. 01, 2022	Jun. 24, 2021	Nov. 07, 2020	Nov. 06, 2020	Feb. 20, 2020	May 19, 2003	Dec. 31, 2021 USD ($) employee acre_foot $ / ft³ $ / million_gallons gal	Dec. 31, 2020 USD ($) gal	Dec. 31, 2019 USD ($) gal	Dec. 31, 2008 $ / yr gal	Dec. 31, 1997	Nov. 02, 2021	Jan. 08, 2020 USD ($)
Long-term Purchase Commitment [Line Items]
Purchased water							$ 98,231	$ 100,723	$ 99,118
Intangible assets							$ 36,276	35,167
Collective bargaining agreement percent of wage increase for 2020					3.00%
Collective bargaining agreement percent of wage increase for 2021					3.00%
Collective bargaining agreement percent of wage increase for 2022					4.00%
SJW Group
Long-term Purchase Commitment [Line Items]
Number of employees \| employee							362
SJW Group \| Union Member
Long-term Purchase Commitment [Line Items]
Number of employees \| employee							226
Minimum
Long-term Purchase Commitment [Line Items]
Useful life of intangible assets							5 years
Maximum
Long-term Purchase Commitment [Line Items]
Useful life of intangible assets							70 years
RWA \| Capacity Agreement
Long-term Purchase Commitment [Line Items]
Current contract water rate (in USD per million of gallons)							2,600			75
Purchase commitment period										14 years
RWA \| Capacity Agreement \| Minimum
Long-term Purchase Commitment [Line Items]
Purchase commitment period										50 years
RWA \| Capacity Agreement \| Maximum
Long-term Purchase Commitment [Line Items]
Agreement to purchase water (in gallons of water) \| gal										1,000,000
MDC \| Capacity Agreement
Long-term Purchase Commitment [Line Items]
Current contract water rate (in USD per million of gallons) \| $ / ft³							4.05
Purchase commitment period						50 years
Agreement to purchase water (in gallons of water) \| gal							283,000,000
Kennebec Water District
Long-term Purchase Commitment [Line Items]
Agreement to purchase water (in gallons of water) \| gal							50,000,000
Contract agreement, term			20 years	20 years
Long-term purchase commitment, wholesale discount (in USD per hundred cubic feet) \| $ / ft³							0.20
Tariff rate (in USD per hundred cubic feet) \| $ / ft³							1.51
International Union of Operating Engineers \| SJW Group
Long-term Purchase Commitment [Line Items]
Bargaining agreements, term					3 years
Service Agreements
Long-term Purchase Commitment [Line Items]
Useful life of intangible assets											25 years
Intangible assets							$ 4,290
Concession fees
Long-term Purchase Commitment [Line Items]
Intangible assets							$ 6,800	$ 6,800					$ 5,000
Lease Term, Option One
Long-term Purchase Commitment [Line Items]
Lease renewal term												6 months
Lease Term, Option One \| Concession fees
Long-term Purchase Commitment [Line Items]
Intangible assets													350
Lease Term, Option Two
Long-term Purchase Commitment [Line Items]
Lease renewal term												2 years
Lease Term, Option Two \| Concession fees
Long-term Purchase Commitment [Line Items]
Intangible assets													1,600
Lease Term, Option Three
Long-term Purchase Commitment [Line Items]
Lease renewal term												3 years
Lease Term, Option Three \| Concession fees
Long-term Purchase Commitment [Line Items]
Intangible assets													$ 2,500
Santa Clara Valley Water District
Long-term Purchase Commitment [Line Items]
Master contract, negotiated term for delivery schedules							3 years
Water purchased (in millions of gallons) \| gal							19,365,000,000	21,269,000,000	21,862,000,000
Purchased water							$ 91,938	$ 96,212	$ 96,285
Reduction in delivery schedule, percent		23.00%
Minimum percent of delivery schedule to be purchased							90.00%
Minimum volume of water to be purchased (in million gallons) \| gal							18,756,000,000
Cost of water to be purchased							$ 92,902
Current contract water rate (in USD per million of gallons) \| $ / million_gallons							5,000.0
Santa Clara Valley Water District \| Subsequent Event
Long-term Purchase Commitment [Line Items]
Increase in delivery schedule, percent	10.00%
Guadalupe-Blanco River Authority \| SJWTX, Inc. dba Canyon Lake Water Supply Corporation
Long-term Purchase Commitment [Line Items]
Long-term purchase commitment, minimum area required (in acre-feet of water) \| acre_foot							7,650
Notice period required for contract adjustment							60 days
Lower Colorado River Authority \| SJWTX, Inc. dba Canyon Lake Water Supply Corporation
Long-term Purchase Commitment [Line Items]
Long-term purchase commitment, minimum area required (in acre-feet of water) \| acre_foot							250