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Contingencies Narrative (Details) $ in Thousands | Feb. 08, 2019 USD ($)
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Subsequent Event [Member] | Advice Letter No. 530 [Member] |
Loss Contingencies [Line Items] |
Approved Service Charge Refund | $ (2,020)

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- Definition Approved Service Charge Refund + References No definition available. + Details
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Namespace Prefix: | sjw_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=sjw_AdviceLetterNo.530Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |