Fair Value of Financial Assets and Liabilities - Narrative (Details)	6 Months Ended
Jun. 30, 2021
Fair Value Disclosures [Abstract]
Risk premium (as a percent)	0.60%

Represents the risk premium rate as an input to measure fair value.

No definition available.

Name:	cwt_FairValueInputsRiskPremium
Namespace Prefix:	cwt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration