Line of Credit Facility, Incremental Expansion of Borrowing Capacity

No definition available.

Name:	cwt_LineofCreditFacilityIncrementalExpansionofBorrowingCapacity
Namespace Prefix:	cwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The effective interest rate during the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=cwt_SeriesWWWMember
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Short-term and Long-term Borrowings (Details) - USD ($)			6 Months Ended
Short-term and Long-term Borrowings (Details) - USD ($)	Jun. 11, 2019	Mar. 29, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 550,000,000
Debt term		5 years
Average borrowing rate			3.33%	2.72%
Revolving Credit Facility \| Minimum
Debt Instrument [Line Items]
Debt term		1 month
Revolving Credit Facility \| Maximum
Debt Instrument [Line Items]
Debt term		6 months
Revolving Credit Facility \| Eurodollar \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		0.65%
Revolving Credit Facility \| Eurodollar \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate		0.875%
Revolving Credit Facility \| Parent Company
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 150,000,000
Available expansion amount		50,000,000
Outstanding borrowings			$ 55,100,000		$ 55,100,000
Cal Water \| Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 400,000,000
Debt term		24 months
Available expansion amount		$ 150,000,000
Outstanding borrowings			$ 110,000,000.0		$ 10,000,000.0
Cal Water \| First Mortgage Bond
Debt Instrument [Line Items]
Debt issued	$ 400,000,000.0
Cal Water \| First Mortgage Bond \| Series UUU
Debt Instrument [Line Items]
Extinguishment of debt	300,000,000.0
Cal Water \| First Mortgage Bond \| Series VVV
Debt Instrument [Line Items]
Debt issued	$ 100,000,000.0
Interest rate	3.40%
Cal Water \| First Mortgage Bond \| Series WWW
Debt Instrument [Line Items]
Debt issued	$ 100,000,000.0
Interest rate	4.07%
Cal Water \| First Mortgage Bond \| Series YYY
Debt Instrument [Line Items]
Debt issued	$ 200,000,000.0
Interest rate	4.17%