This represents the under-collection or over-collection associated with expense changes and the revenue authorized by the CPUC to offset those expense changes. Pursuant to Section 792.5 of the California Public Utilities Code, a balancing account must be maintained for expense items for which revenue offsets have been authorized. Since the amounts in the balancing accounts must be approved by the CPUC before they can be incorporated into rates, the Company does not recognize balancing accounts in its revenue until CPUC approval occurs. It is typical for the CPUC to incorporate any over-collected and/or under-collected balances in balancing accounts into customer rates at the time rate decisions are made as part of the Company’s general rate case proceedings by assessing temporary surcredits and/or surcharges.

No definition available.

Name:	sjw_BalancingAccountNet
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

General - Additional Information (Details) - USD ($) $ in Thousands	Jun. 14, 2016	Nov. 24, 2015	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Regulatory Assets [Line Items]
Water reduction target goal (percent)	20.00%	30.00%
Balancing Account, Net			$ 29,823	$ 38,013	$ 36,296	$ 34,359	$ 42,950	$ 48,437
Drought surcharges
Regulatory Assets [Line Items]
Balancing Account, Net			$ (6,320)	$ (1,716)	$ (359)	$ (6,413)	$ (80)	$ 0