Regulatory Matters - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended		9 Months Ended
	Oct. 31, 2025	Aug. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024
Regulatory matters:
Net regulatory Assets			$ 29,184		$ 54,679
Receivables from litigation settlement			12,327		6,415
Golden State Water Company and Bear Valley Electric Service Inc.
Regulatory matters:
Net regulatory Assets			29,200
Regulatory asset			135,900
Regulatory liability			$ 106,700
Commercial paper, term			90 days
Regulatory asset not accruing carrying costs			$ 38,300
Regulatory liabilities not accruing carrying costs			102,600
Golden State Water Company and Bear Valley Electric Service Inc. | Deferred Income Tax Charge
Regulatory matters:
Regulatory liabilities not accruing carrying costs			67,200
Golden State Water Company and Bear Valley Electric Service Inc. | Pension Costs and Other Postretirement Benefit Costs
Regulatory matters:
Regulatory liabilities not accruing carrying costs			23,000
Golden State Water Company and Bear Valley Electric Service Inc. | PFAS Contamination Litigation Proceeds Memorandum Account
Regulatory matters:
Regulatory liabilities not accruing carrying costs			12,400
GSWC
Regulatory matters:
Net regulatory Assets			(13,874)		18,173
Litigation settlement, amount awarded			19,000
Receivables from litigation settlement			10,703		3,122
Proceeds from legal settlements		$ 3,800
Litigation settlement, amounts expected to be received			6,500
GSWC | Subsequent Event
Regulatory matters:
Proceeds from legal settlements	$ 12,500
GSWC | Legal settlement receivable
Regulatory matters:
Receivables from litigation settlement				$ 12,500
GSWC | Deferred Income Tax Charge
Regulatory matters:
Net regulatory Assets			(63,464)		(63,682)
GSWC | Pension Costs and Other Postretirement Benefit Costs
Regulatory matters:
Net regulatory Assets			(24,578)		(25,179)
GSWC | PFAS Contamination Litigation Proceeds Memorandum Account
Regulatory matters:
Net regulatory Assets			(12,393)		0
BVES
Regulatory matters:
Net regulatory Assets			43,058		36,506
Flowed-through deferred income taxes, net | Golden State Water Company and Bear Valley Electric Service Inc.
Regulatory matters:
Regulatory asset not accruing carrying costs			21,000
Flowed-through deferred income taxes, net | GSWC
Regulatory matters:
Net regulatory Assets			18,668		12,506
Derivative instrument memorandum account (Note 5)
Regulatory matters:
Regulatory asset not accruing carrying costs			14,300
Derivative instrument memorandum account (Note 5) | BVES
Regulatory matters:
Net regulatory Assets			14,275		8,823
Other Regulatory assets | Golden State Water Company and Bear Valley Electric Service Inc.
Regulatory matters:
Regulatory asset not accruing carrying costs			3,000
2025 general rate case memorandum accounts (unbilled revenue) | GSWC
Regulatory matters:
Net regulatory Assets			$ 2,614		0
Amortization period			12 months
2022/2023 general rate case memorandum accounts (unbilled revenue) | GSWC
Regulatory matters:
Net regulatory Assets			$ 25,864		37,711
Water revenue adjustment mechanism, net of modified cost balancing account | GSWC
Regulatory matters:
Net regulatory Assets			$ 12,752		29,738
Regulatory asset recovery periods			18 months
Water Revenue Adjustment Mechanism ("WRAM") | GSWC
Regulatory matters:
Net regulatory Assets			$ 12,300
Modified Cost Balancing account ("MCBA") | GSWC
Regulatory matters:
Net regulatory Assets			500
2023/2024 General Rate Case Memorandum accounts ( unbilled revenue) | BVES
Regulatory matters:
Net regulatory Assets			$ 8,949		9,777
Amortization period			36 months
Wildfire mitigation and other fire prevention related costs memorandum accounts | BVES
Regulatory matters:
Net regulatory Assets			$ 13,030		$ 14,681
Vegetation management and other WMP memorandum accounts | BVES | Minimum
Regulatory matters:
Amortization period			24 months
Vegetation management and other WMP memorandum accounts | BVES | Maximum
Regulatory matters:
Amortization period			36 months