Lines of Credit Narrative (Details) (USD $)	12 Months Ended
Dec. 31, 2014 standy_letter_of_credit	Dec. 31, 2013
Unsecured Debt [Member] \| Wells Fargo [Member] \| SJW Corp. [Member]
Ratio of indebtedness to total capital	0.666
Debt covenant interest charge maximum to net Income available to stockholders	1.75
Revolving Credit Facility [Member]
Aggregate amount of unsecured revolving credit facility	$ 100,000,000
Revolving Credit Facility [Member] \| SJW Corp. [Member]
Aggregate outstanding balance on lines of credit	13,200,000	22,400,000
Line of Credit Facility, Interest Rate at Period End	1.15%	1.29%
Revolving Credit Facility [Member] \| Wells Fargo [Member] \| SJW Corp., SJW Land Company [Member]
Aggregate amount of unsecured revolving credit facility	15,000,000
Revolving Credit Facility [Member] \| Wells Fargo [Member] \| San Jose Water Company [Member]
Aggregate amount of unsecured revolving credit facility	85,000,000	75,000,000
Standby Letters of Credit [Member] \| San Jose Water Company [Member]
Aggregate amount of unsecured revolving credit facility	$ 3,000,000
Number of standby letters of credit	2
Automatic renewal term of standby letters of credit	1 year

Debt, Covenant, Interest Charge Maximum to Net Income Available to Stockholders

No definition available.

Name:	sjw_DebtCovenantInterestChargeMaximumtoNetIncomeAvailabletoStockholders
Namespace Prefix:	sjw_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Number of Standby Letters of Credit

+ References

No definition available.

+ Details

Name:	sjw_LineOfCreditFacilityNumberOfStandbyLettersOfCredit
Namespace Prefix:	sjw_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Standby Letter Of Credit, Automatic Renewal Term

+ References

No definition available.

+ Details

Name:	sjw_LineOfCreditFacilityStandbyLetterOfCreditAutomaticRenewalTerm
Namespace Prefix:	sjw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Ratio of Indebtedness to Total Capital

+ References

No definition available.

+ Details

Name:	sjw_RatioOfIndebtednessToCapital
Namespace Prefix:	sjw_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- 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://www.xbrl.org/2003/role/presentationRef

-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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-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=6879938&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 at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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

- 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

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

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_UnsecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: