Summary of Significant Accounting Policies - Narrative (Details)	9 Months Ended
Sep. 30, 2025
Accounting Policies [Abstract]
Maximum collection period in which deferred net WRAM and MCBA revenues and associated costs will be recognized	24 months

Represents the maximum collection period in which deferred net WRAM and MCBA revenues and associated costs will be recognized.

No definition available.

Name:	cwt_MaximumCollectionPeriodInWhichDeferredNetWRAMAndMCBARevenuesAndAssociatedCostsWillBeRecognized
Namespace Prefix:	cwt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration