Financial Statement Schedule - Narrative (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Condensed Financial Information Disclosure [Abstract]
Restricted net assets, subsidiaries	$ 494,699
Restricted net assets, subsidiaries, percent of consolidated assets	36.00%

Restricted Net Assets, Subsidiaries, Percent Of Consolidated Assets

No definition available.

Name:	sjw_RestrictedNetAssetsSubsidiariesPercentOfConsolidatedAssets
Namespace Prefix:	sjw_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant