Commitments (Details) $ / billionGallon in Thousands, $ in Thousands						1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 12, 2024	May 19, 2023 gal	Nov. 07, 2020 $ / ft³ gal	Nov. 06, 2020	May 19, 2003	Oct. 31, 2024 USD ($) serviceConnection	Mar. 31, 2023	Dec. 31, 2024 USD ($) acre_foot employee $ / billionGallon $ / ft³ gal	Dec. 31, 2023 USD ($) gal	Dec. 31, 2022 USD ($) gal	Dec. 31, 2008 gal
Long-term Purchase Commitment [Line Items]
Purchased water | $								$ 158,568	$ 135,982	$ 122,334
Number of service connections | serviceConnection						4,700
Service agreement, term of contract						12 years
Service agreement, renewal term						8 years
Service agreement, upfront concession fee | $						$ 22,100
Service agreement, annual rent expense | $						$ 1,800
Union Member
Long-term Purchase Commitment [Line Items]
Collective bargaining agreement percent of wage increase for 2023							6.00%
Collective bargaining agreement percent of wage increase for 2024							3.50%
Collective bargaining agreement percent of wage increase for 2025							5.50%
SJW Group
Long-term Purchase Commitment [Line Items]
Number of employees | employee								395
SJW Group | Union Member
Long-term Purchase Commitment [Line Items]
Number of employees | employee								241
RWA | Capacity Agreement
Long-term Purchase Commitment [Line Items]
Current contract water rate | $ / billionGallon								3,100
RWA | Maximum | Capacity Agreement
Long-term Purchase Commitment [Line Items]
Agreement to purchase water (in gallons of water) | gal											1,000,000
MDC | Capacity Agreement
Long-term Purchase Commitment [Line Items]
Current contract water rate | $ / ft³								3.80
Agreement to purchase water (in gallons of water) | gal		280,000,000
Purchase commitment period					50 years
Kennebec Water District
Long-term Purchase Commitment [Line Items]
Agreement to purchase water (in gallons of water) | gal			50,000,000.00
Long-term purchase commitment, wholesale discount (in USD per hundred cubic feet) | $ / ft³			0.20
Contract agreement, term			20 years	20 years
Tariff rate (in USD per hundred cubic feet) | $ / ft³								1.51
International Union of Operating Engineers | SJW Group
Long-term Purchase Commitment [Line Items]
Bargaining agreements, term							3 years
Santa Clara Valley Water District
Long-term Purchase Commitment [Line Items]
Master contract, negotiated term for delivery schedules								3 years
Water purchased (in gallons) | gal								17,000,000,000.0	18,300,000,000	18,200,000,000
Purchased water | $								$ 117,698	$ 111,173	$ 96,793
Reduction in delivery schedule, percent	23.00%
Minimum percent of delivery schedule to be purchased								90.00%
Minimum volume of water to be purchased (in gallons) | gal								18,900,000,000
Cost of water to be purchased | $								$ 135,975
Current contract water rate | $ / billionGallon								7,194
Guadalupe-Blanco River Authority | SJWTX, Inc.
Long-term Purchase Commitment [Line Items]
Long-term purchase commitment, minimum area required (in acre-feet of water) | acre_foot								7,602
Notice period required for contract adjustment								60 days
Lower Colorado River Authority | SJWTX, Inc.
Long-term Purchase Commitment [Line Items]
Long-term purchase commitment, minimum area required (in acre-feet of water) | acre_foot								350