Regulatory Matters - Regulatory Assets, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Regulatory Assets [Line Items]
Regulatory assets	$ 146,683	$ 154,621
Less: current regulatory assets, net	738	2,629
Total regulatory assets, net, less current portion	145,945	151,992
Regulatory assets, net not earning a return	86,113	84,887
Income tax temporary differences, net
Regulatory Assets [Line Items]
Regulatory assets	33,811	22,420
Postretirement pensions and other postretirement benefits
Regulatory Assets [Line Items]
Regulatory assets	64,934	62,197
Business combinations debt premium, net
Regulatory Assets [Line Items]
Regulatory assets	18,031	19,937
Balancing and memorandum accounts, net
Regulatory Assets [Line Items]
Regulatory assets	22,583	38,334
Water Rate Adjustment
Regulatory Assets [Line Items]
Regulatory assets	(2,800)	2,588
Other, net
Regulatory Assets [Line Items]
Regulatory assets	$ 10,124	$ 9,145

The net amount of all regulatory assets less all regulatory liabilities as of the end of the period.

Name:	us-gaap_NetRegulatoryAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_RegulatoryAssetLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

+ Details

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

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

+ Details

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

- Definition

Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 55
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=123406419&loc=d3e44360-110383

+ Details

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

- Details

Name:	us-gaap_RegulatoryAssetAxis=us-gaap_DeferredIncomeTaxChargesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=sjw_PostretirementPensionsAndOtherMedicalBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=sjw_BusinessCombinationsDebtPremiumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=sjw_BalancingandMemorandumAccountsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=sjw_WRAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=sjw_OtherRegulatoryAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: