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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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