Regulatory Matters - Narrative (Details) - USD ($) $ in Thousands			1 Months Ended	6 Months Ended
	Jul. 23, 2026	Jun. 23, 2026	Jun. 30, 2026	Jun. 30, 2026	Dec. 31, 2025
Regulatory matters:
Net regulatory liability			$ 13,971	$ 13,971	$ (9,264)
Golden State Water Company and Bear Valley Electric Service Inc.
Regulatory matters:
Net regulatory liability			14,000	14,000
Regulatory asset			114,900	114,900
Regulatory liability			128,900	$ 128,900
Commercial paper, term				90 days
Regulatory asset not accruing carrying costs			45,800	$ 45,800
Regulatory liabilities not accruing carrying costs			124,300	124,300
Golden State Water Company and Bear Valley Electric Service Inc. | Deferred Income Tax Charge
Regulatory matters:
Regulatory liabilities not accruing carrying costs			66,800	66,800
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			40,600	40,600
Golden State Water Company and Bear Valley Electric Service Inc. | PFAS Contamination Litigation Proceeds Memorandum Account
Regulatory matters:
Regulatory liabilities not accruing carrying costs			16,900	16,900
GSWC
Regulatory matters:
Net regulatory liability			53,663	53,663	36,994
GSWC | Tyco
Regulatory matters:
Proceeds from legal settlements			2,200
GSWC | 3M
Regulatory matters:
Proceeds from legal settlements		$ 3,300
Litigation settlement, amounts expected to be received			3,300	3,300
GSWC | 3M | Subsequent Event
Regulatory matters:
Proceeds from legal settlements	$ 3,300
GSWC | BASF
Regulatory matters:
Proceeds from legal settlements			900
GSWC | Deferred Income Tax Charge
Regulatory matters:
Regulatory liability			63,081	63,081	63,223
GSWC | Pension Costs and Other Postretirement Benefit Costs
Regulatory matters:
Regulatory liability			44,502	44,502	43,479
GSWC | PFAS Contamination Litigation Proceeds Memorandum Account
Regulatory matters:
Regulatory liability			16,851	16,851	10,987
Flowed-through deferred income taxes, net | Golden State Water Company and Bear Valley Electric Service Inc.
Regulatory matters:
Regulatory asset not accruing carrying costs			27,900	27,900
Flowed-through deferred income taxes, net | GSWC
Regulatory matters:
Regulatory asset			24,260	24,260	20,932
Derivative instrument memorandum account (Note 5)
Regulatory matters:
Regulatory asset not accruing carrying costs			14,600	14,600
Other Regulatory assets | Golden State Water Company and Bear Valley Electric Service Inc.
Regulatory matters:
Regulatory asset not accruing carrying costs			3,300	3,300
2022/2023 general rate case memorandum accounts (unbilled revenue) | GSWC
Regulatory matters:
Regulatory asset			$ 14,632	$ 14,632	$ 22,107