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Financial Statement Schedule - Narrative (Details) $ in Thousands | Dec. 31, 2021 USD ($)
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Condensed Financial Information Disclosure [Abstract] |
Restricted net assets, subsidiaries | $ 337,787
Restricted net assets, subsidiaries, percent of consolidated assets | 33.00%

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- Definition Restricted Net Assets, Subsidiaries + References No definition available. + Details
Name: | sjw_RestrictedNetAssetsSubsidiaries
Namespace Prefix: | sjw_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Restricted Net Assets, Subsidiaries, Percent Of Consolidated Assets + References No definition available. + Details
Name: | sjw_RestrictedNetAssetsSubsidiariesPercentOfConsolidatedAssets
Namespace Prefix: | sjw_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
Name: | srt_CondensedFinancialInformationOfParentCompanyOnlyDisclosureAbstract
Namespace Prefix: | srt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration