Contingencies (Details) - Environmental Clean-Up and Remediation - GOLDEN STATE WATER COMPANY $ in Millions	Sep. 30, 2025 USD ($) plantSite
Loss Contingencies [Line Items]
Number of plant facilities | plantSite	1
Environmental costs recognized, capitalized	$ 6.9
Environmental loss contingencies paid by third party	1.5
Accrued liability for the estimated additional cost to complete the clean-up at the site	$ 1.3