Regulatory Matters - Narrative (Details)				3 Months Ended	9 Months Ended	12 Months Ended
	Jul. 31, 2023	Jun. 30, 2023	Jun. 29, 2023	Mar. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2024	Sep. 30, 2023 USD ($)	Sep. 30, 2022	Apr. 10, 2023 USD ($)	Dec. 31, 2022 USD ($)
Regulatory matters:
Regulatory asset not accruing carrying costs					$ 67,100,000		$ 67,100,000
Net regulatory Assets					77,667,000		77,667,000			$ (25,454,000)
Regulatory asset amount billed to customers as surcharges					$ 0
Cost of capital proceeding
Regulatory matters:
Adjustment to return on equity, if more than 100 basis point change					0.5
Threshold percentage of Moody's average bond rate used adjusting return on equity and rate of return on rate base, increase (decrease)					0.0100
GSWC
Regulatory matters:
Net regulatory Assets					$ 60,866,000		60,866,000			(26,574,000)
Approved equity capital structure (in percent)			57.00%
Approved debt capital structure (in percent)			43.00%
Approved debt capital structure, percentage previously authorized					6.60%
Approved return on equity previously authorized (in percent)					8.90%
Regulatory asset-CEMA					$ 3,500,000		$ 3,500,000
GSWC | Cost of capital proceeding
Regulatory matters:
Approved debt capital structure in May 2021 cost of capital application (in percent)					5.10%
Approved return on equity in May 2021 cost of capital application (in percent)		8.85%
Term for the cost of capital proceeding					3 years
Revenue impact due to lower cost of debt					$ 6,400,000
Triggers for the WCMA adjustment, impact of 103 Basis Point increase in Moody's Rate (in percent)							0.01397	0.01028
Requested return on equity (in percent)	9.36%
GSWC | Cost of capital proceeding | Subsequent Event
Regulatory matters:
Approved return on equity in May 2021 cost of capital application (in percent)						9.36%
Requested return on equity (in percent)						10.06%
BVES
Regulatory matters:
Regulatory asset-CEMA					500,000		$ 500,000		$ 0
Regulatory Asset -incremental vegetation management costs					10,900,000		10,900,000
Regulatory asset- wildfire mitigation plans (WMP)					5,500,000		5,500,000
Regulatory asset CEMA - Storm					1,300,000		1,300,000
2022/2023 general rate case memorandum accounts (unbilled revenue) | GSWC
Regulatory matters:
Net regulatory Assets					$ 55,140,000		$ 55,140,000			0
Amortization period					36 months		36 months
Water revenue adjustment mechanism, net of modified cost balancing account
Regulatory matters:
Increase (decrease) in other regulatory assets				$ (9,800,000)	$ 34,900,000
Regulatory asset recovery periods					24 months
Water revenue adjustment mechanism, net of modified cost balancing account | GSWC
Regulatory matters:
Net regulatory Assets					$ 46,597,000		$ 46,597,000			31,803,000
Commercial paper, term					90 days
Excess deferred income taxes
Regulatory matters:
Regulatory asset not accruing carrying costs					$ 74,400,000		74,400,000
Excess deferred income taxes | GSWC
Regulatory matters:
Net regulatory Assets					(70,515,000)		(70,515,000)			(71,870,000)
Derivative instrument memorandum account (Note 5)
Regulatory matters:
Regulatory asset not accruing carrying costs					1,500,000		1,500,000
Derivative instrument memorandum account (Note 5) | BVES
Regulatory matters:
Net regulatory Assets					(1,525,000)		(1,525,000)			$ (11,847,000)
Pension Costs and Other Postretirement Benefit Costs [Member]
Regulatory matters:
Regulatory asset not accruing carrying costs					2,600,000		2,600,000
Modified Cost Balancing account ("MCBA") | GSWC
Regulatory matters:
Net regulatory Assets					(4,600,000)		(4,600,000)
Water Revenue Adjustment Mechanism ("WRAM") | GSWC
Regulatory matters:
Net regulatory Assets					$ 51,200,000		$ 51,200,000