Lines of Credit Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Mar. 01, 2020 USD ($)	Dec. 31, 2018 USD ($)	Jun. 01, 2016 USD ($)
Document Period End Date	Dec. 31, 2019
Revolving Credit Facility [Member] | SJW Group [Member]
Aggregate outstanding balance on lines of credit	$ 117,209		$ 100,000
Unsecured Debt [Member] | Chase Bank, N.A. [Member] | SJW Group [Member]
Debt covenant interest charge maximum to net Income available to stockholders	1.75
Ratio of indebtedness to total capital	0.666
Line of Credit [Member] | Revolving Credit Facility [Member] | SJW Group [Member]
Line of Credit Facility, Interest Rate at Period End	3.73%		2.94%
Line of Credit [Member] | Revolving Credit Facility [Member] | Chase Bank, N.A. [Member] | SJW Corp. and SJW Land Company [Member]
LIne of credit facility, maximum borrowing capacity				$ 15,000
Line of Credit [Member] | Revolving Credit Facility [Member] | CoBank [Member] | Connecticut Water Service, Inc. [Member]
LIne of credit facility, maximum borrowing capacity	$ 15,000
Line of Credit [Member] | Revolving Credit Facility [Member] | RBS Citizens, N.A. [Member] | Connecticut Water Service, Inc. [Member]
LIne of credit facility, maximum borrowing capacity	$ 95,000
Line of Credit [Member] | Credit Agreement [Member] | Chase Bank, N.A. [Member] | San Jose Water Company [Member]
LIne of credit facility, maximum borrowing capacity				125,000
Line of Credit [Member] | Credit Agreement [Member] | Standby Letters of Credit [Member] | Chase Bank, N.A. [Member] | San Jose Water Company [Member]
LIne of credit facility, maximum borrowing capacity				10,000
Line of Credit [Member] | SJW Corp Credit Agreement [Member] | Standby Letters of Credit [Member] | Chase Bank, N.A. [Member] | SJW Corp. and SJW Land Company [Member]
LIne of credit facility, maximum borrowing capacity				5,000
Line of Credit [Member] | SJWTX Credit Agreement [Member] | Revolving Credit Facility [Member] | Chase Bank, N.A. [Member] | SJW Corp. and SJWTX, Inc. [Member]
LIne of credit facility, maximum borrowing capacity				5,000
Line of Credit [Member] | SJWTX Credit Agreement [Member] | Standby Letters of Credit [Member] | Chase Bank, N.A. [Member] | SJW Corp. and SJWTX, Inc. [Member]
LIne of credit facility, maximum borrowing capacity				$ 1,000
Subsequent Event [Member] | Line of Credit [Member] | Revolving Credit Facility [Member] | RBS Citizens, N.A. [Member] | Connecticut Water Service, Inc. [Member]
LIne of credit facility, maximum borrowing capacity		$ 75,000