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Document and Entity Information Document - shares
6 Months Ended
Jun. 30, 2020
Aug. 04, 2020
Document and Entity Information [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2020  
Entity File Number 1-8966  
Entity Registrant Name SJW GROUP  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 77-0066628  
Entity Address, Address Line One 110 West Taylor Street,  
Entity Address, City or Town San Jose,  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 95110  
City Area Code (408)  
Local Phone Number 279-7800  
Entity Listing, Description Common Stock, par value $0.001 per share  
Trading Symbol SJW  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   28,532,903
Entity Central Index Key 0000766829  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Document Transition Report false