Summary of Significant Accounting Policies (Narrative) (Details)				3 Months Ended	12 Months Ended
	Feb. 03, 2020 USD ($)	Sep. 14, 2018 USD ($)	Nov. 16, 2017 USD ($)	Dec. 31, 2019 USD ($) mi² people_served service_connection communities_served	Dec. 31, 2019 USD ($) mi² people_served service_connection communities_served	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 06, 2019 USD ($)
Public Utilities, General Disclosures [Line Items]
Gain on sale of real estate investments					$ 929,000	$ 0	$ 6,903,000
Balancing and Memorandum Revenue Account, Increase (Decrease)					(4,984,000)	3,827,000
Balancing and Memorandum Account, Refunds (Collections)					(25,108,000)	18,000	(21,206,000)
Restricted Cash				$ 750,000	$ 750,000
Document Period End Date					Dec. 31, 2019
Proceeds from Sale of Real Estate Held-for-investment				$ 745,000
Long-term borrowings held as restricted cash					$ 5,000,000	$ 0	$ 0
Acequia Water Supply Corporation [Member]
Public Utilities, General Disclosures [Line Items]
Ownership percentage in Acequia Water Supply Corporation					25.00%
Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Service area in square miles | mi²				246	246
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
Sales [Member] | Product Concentration Risk [Member]
Public Utilities, General Disclosures [Line Items]
Percentage of revenue derived from sales of water to business and residential customers					91.00%
San Jose Water Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Service Connections | service_connection				231,000	231,000
Number of people served | people_served				1,000,000,000,000	1,000,000,000,000
Connecticut Water Service, Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Number of people served | people_served				480,000	480,000
Public Utilities, Number of Communities Served | communities_served				80	80
444 West Santa Clara Street, L.P. [Member]
Public Utilities, General Disclosures [Line Items]
Limited partership interest percentage					70.00%
Maine Water Company [Member]
Public Utilities, General Disclosures [Line Items]
Gain on sale of real estate investments					$ 180,000
Proceeds from Sale of Real Estate Held-for-investment					600,000
Long-term borrowings held as restricted cash					$ 5,000,000
SJWTX,Inc. dba Canyon Lake Water Supply Corporation [Member]
Public Utilities, General Disclosures [Line Items]
Number of people served | people_served				54,000	54,000
Texas Water Alliance Alliance [Member]
Public Utilities, General Disclosures [Line Items]
Proceeds from Sales of Business, Affiliate and Productive Assets			$ 31,000,000
Purchase and Sales Agreement, Holdback Amount			3,000,000
Gain (Loss) on Disposition of Assets			$ 12,501,000
Subsequent Event [Member] | Maine Water Company [Member]
Public Utilities, General Disclosures [Line Items]
Increase (Decrease) in Restricted Cash	$ 4,114,000
Application No. 19-12-002 [Member] | San Jose Water Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Rate Filings, Requested Rate Increase, Year One								$ 2,300,000
Connecticut and Maine | Connecticut Water Service, Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Service Connections | service_connection				137,000	137,000
Connecticut | Connecticut Water Service, Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Service Connections | service_connection				3,000	3,000