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v3.21.2

Segment and Non-Tariffed Business Reporting - Narrative (Details) | 9 Months Ended
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Sep. 30, 2021 subsidiary
Segment Reporting [Abstract] |
Number of subsidiaries | 4

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- Definition Number of Subsidiaries + References No definition available. + Details
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Namespace Prefix: | sjw_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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