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SJW Group and CTWS Merger (the “Merger”) (Details) | Mar. 14, 2018 $ / shares
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CTWS [Member] |
Business Acquisition [Line Items] |
Acquiree's common shares converted in cash (in USD per share) | $ 70.00

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- Definition Business Combination, Consideration Transferred, Acquiree's Common Shares Converted In Cash Per Share + References No definition available. + Details
Name: | sjw_BusinessCombinationConsiderationTransferredAcquireesCommonSharesConvertedInCashPerShare
Namespace Prefix: | sjw_
Data Type: | num:perShareItemType
Balance Type: | na
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
Name: | us-gaap_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_BusinessAcquisitionAxis=sjw_CTWSMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |