Commitments (Details) $ / billions_gallons in Thousands, $ in Thousands						3 Months Ended	12 Months Ended
	May 19, 2023 gal	Jun. 16, 2022	Nov. 07, 2020 $ / ft³ gal	Nov. 06, 2020	May 19, 2003	Mar. 31, 2023	Dec. 31, 2023 USD ($) employee acre_foot $ / billions_gallons $ / ft³ gal	Dec. 31, 2022 USD ($) gal	Dec. 31, 2021 USD ($) gal	Dec. 31, 2008 gal	Dec. 31, 1997 USD ($)	Feb. 25, 2022 USD ($)
Long-term Purchase Commitment [Line Items]
Purchased water							$ 135,982	$ 122,334	$ 98,231
Contract agreement, incremental up-front payment											$ 5,000
Intangible assets							$ 35,946	35,959
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							387
SJW Group | Union Member
Long-term Purchase Commitment [Line Items]
Number of employees | employee							240
Maximum
Long-term Purchase Commitment [Line Items]
Useful life of intangible assets							70 years
RWA | Capacity Agreement
Long-term Purchase Commitment [Line Items]
Current contract water rate (in USD per million of gallons) | $ / billions_gallons							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 (in USD per million of gallons) | $ / ft³							3.80
Purchase commitment period					50 years
Agreement to purchase water (in gallons of water) | gal	280,000,000
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
Service Agreements
Long-term Purchase Commitment [Line Items]
Useful life of intangible assets											25 years
Intangible assets							$ 4,292
Concession fees
Long-term Purchase Commitment [Line Items]
Intangible assets							$ 6,800	$ 6,800			$ 6,800	$ 1,600
Lease renewal term												2 years
Santa Clara Valley Water District
Long-term Purchase Commitment [Line Items]
Master contract, negotiated term for delivery schedules							3 years
Water purchased (in millions of gallons) | gal							18,300,000,000	18,200,000,000	19,400,000,000
Purchased water							$ 111,173	$ 96,793	$ 91,938
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 million gallons) | gal							18,900,000,000
Cost of water to be purchased							$ 121,182
Current contract water rate (in USD per million of gallons) | $ / billions_gallons							6,411
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							7,650
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