Regulatory Rate Filings (Details) - USD ($) $ in Thousands					3 Months Ended	11 Months Ended	12 Months Ended
	Apr. 19, 2018	Mar. 22, 2018	Nov. 29, 2017	Nov. 15, 2017	Mar. 31, 2018	Nov. 28, 2017	Dec. 31, 2017	Jan. 04, 2018
Public Utilities, General Disclosures [Line Items]
Revenue increase amount				$ 15,670
Revenue increase, percentage				4.22%
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%
Public Utilities, Approved Equity Capital Structure, Decrease, Amount					$ 5,843
Public Utilities, Approved Equity Capital Structure, Decrease, Percent					1.57%
Regulatory Rate Filings, Requested Rate Increase, Year One								$ 34,288
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
Regulatory Rate Filings, Proposed Rate Increase, Percent of Authorized Revenue, Year Two								3.70%
Regulatory Rate Filings, Requested Rate Increase, Year Three								$ 20,582
Regulatory Rate Filings, Requested Rate Increase, Percent of Authorized Revenue, Year Three								5.17%
Memorandum Account, Authorized Recovery								$ 20,725
SJWTX, Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Liability, Current					$ 139
Subsequent Event [Member] | SJWTX, Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ (745)