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Summary of Significant Accounting Policies (Regulatory Rate Filings) (Details) - USD ($)								12 Months Ended
	Dec. 04, 2018	Sep. 14, 2018	Aug. 25, 2018	Jul. 31, 2018	Jul. 01, 2018	Jan. 01, 2018	Apr. 03, 2017	Dec. 31, 2018	Dec. 31, 2017	Feb. 08, 2019	Jan. 04, 2018	Jun. 06, 2017
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Reimbursement Fee, Percentage						1.40%			1.44%
Public Utilities, Requested Equity Capital Structure, Percentage							8.09%
Public Utilities, Approved Equity Capital Structure, Percentage						7.64%
Requested rate increase for 2019											$ 34,288,000
Balancing and Memorandum Revenue Account, Increase (Decrease)								$ 3,827,000
Requested rate increase for 2019 as percentage of total revenue at time of request											9.76%
Requested rate increase for 2020											$ 14,232,000
Requested rate increase for 2020 as percentage of total revenue at time of request											3.70%
Requested rate increase for 2021											$ 20,582,000
Requested rate increase for 2021 as percentage of total revenue at time of request											5.17%
Memorandum Account, Authorized Recovery											$ 20,725,000
CPED Calculated Double-Billing Refund		$ 4,935,000
SJWTX, Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount								$ 927,000
Authorized Regulatory Surcharge, Per Thousand Gallons				$ 1.13		$ 1.15
CPED Calculated Refund 2014-2016 [Member]
Public Utilities, General Disclosures [Line Items]
CPED Calculated Service Charge Refund		2,061,000
CPED Calculated Refund 1987-2013 [Member]
Public Utilities, General Disclosures [Line Items]
CPED Calculated Service Charge Refund		1,990,000
Advice Letter No. 513/513A [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount						$ (15,670,000)
Public Utilities, Approved Rate Increase (Decrease), Percentage						(4.22%)
Advice Letter No. 518 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount						$ 5,843,000
Public Utilities, Approved Rate Increase (Decrease), Percentage						1.57%
Advice Letter No. 528/528A [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 16,378,000
Public Utilities, Requested Rate Increase (Decrease), Percentage	4.55%
Advice Letter No. 522A [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 14,801,000
Public Utilities, Approved Rate Increase (Decrease), Percentage					3.89%
Advice Letter No. 523 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount					$ (13,732,000)
Public Utilities, Approved Rate Increase (Decrease), Percentage					(3.75%)
Advice Letter No. 524 [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount			$ (3,155,000)
Public Utilities, Approved Rate Increase (Decrease), Percentage			(0.83%)
Advice Letter No. 510 [Member]
Public Utilities, General Disclosures [Line Items]
Requested Service Charge Refund												$ 1,794,000
Advice Letter No. 530 [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Approved Service Charge Refund										$ (2,020,000)
Minimum [Member]
Public Utilities, General Disclosures [Line Items]
CPED Proposed Penalty, Per Offense, Per Day		500
Maximum [Member]
Public Utilities, General Disclosures [Line Items]
CPED Proposed Penalty, Per Offense, Per Day		$ 50,000

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