Regulatory Matters - Balancing and Memorandum Accounts (Details)	Mar. 31, 2022
Regulated Operations [Abstract]
Authorized revenue, threshold percentage	2.00%

Threshold balance of regulatory balancing or memorandum accounts as a percentage of authorized revenue to trigger an account review.

No definition available.

Name:	sjw_RegulatoryBalancingandMemorandumAccountsReviewAuthorizedRevenueThresholdPercentage
Namespace Prefix:	sjw_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant