Regulatory Rate Filings (Details) - USD ($)							12 Months Ended
	Sep. 14, 2018	Jul. 31, 2018	Jul. 26, 2018	Jun. 13, 2018	Jun. 07, 2018	Jan. 01, 2018	Dec. 31, 2018	Jan. 04, 2018	Jun. 06, 2017
Public Utilities, General Disclosures [Line Items]
Regulatory Rate Filings, Requested Rate Increase, Year One								$ 34,288,000
Regulatory Rate Filings, Requested Rate Increase as Percentage of Total Revenue at Time of Request, Year One								9.76%
Regulatory Rate Filings, Requested Rate Increase, Year Two								$ 14,232,000
Regulatory Rate Filings, Proposed Rate Increase, Percent of Authorized Revenue, Year Two								3.70%
Regulatory Rate Filings, Requested Rate Increase, Year Three								$ 20,582,000
Regulatory Rate Filings, Requested Rate Increase, Percent of Authorized Revenue, Year Three								5.17%
Memorandum Account, Authorized Recovery								$ 20,725,000
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 3,155,000	$ 13,732,000	$ (14,801,000)
Public Utilities, Requested Rate Increase (Decrease), Percentage			0.83%	3.75%	(3.89%)
CPED Calculated Double-Billing Refund	$ 4,935,000
SJWTX, Inc.
Public Utilities, General Disclosures [Line Items]
Authorized Regulatory Surcharge, Per Thousand Gallons		$ 1.13				$ 1.15
Scenario, Forecast | SJWTX, Inc.
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Decrease, Amount							$ 1,023,000
Minimum
Public Utilities, General Disclosures [Line Items]
CPED Proposed Penalty, Per Offense, Per Day	500
Maximum
Public Utilities, General Disclosures [Line Items]
CPED Proposed Penalty, Per Offense, Per Day	50,000
Cal PA Complaint 17-06-009
Public Utilities, General Disclosures [Line Items]
Requested Service Charge Refund									$ 1,794,000
CPED Calculated Refund 2014-2016
Public Utilities, General Disclosures [Line Items]
CPED Calculated Service Charge Refund	2,061,000
CPED Calculated Refund 1987-2013
Public Utilities, General Disclosures [Line Items]
CPED Calculated Service Charge Refund	$ 1,990,000