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

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 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://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

Reference 3: 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

+ 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

+ 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

- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

+ Details

Name:	us-gaap_RepaymentsOfLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_ConsolidatedEntitiesAxis=us-gaap_ParentCompanyMember
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:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=sjw_ChaseBankN.A.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sjw_SJWCorp.andSJWLandCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=sjw_CreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sjw_SanJoseWaterCompanyMember
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_DebtInstrumentAxis=sjw_SJWCorpCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=sjw_SJWTXCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sjw_SJWCorp.andSJWTXInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Lines of Credit Narrative (Details) $ in Thousands	12 Months Ended
Lines of Credit Narrative (Details) $ in Thousands	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 01, 2016 USD ($)
Repayments of Long-term Debt	$ 2,717	$ 16,599	$ 633
Revolving Credit Facility [Member] \| SJW Group [Member]
Aggregate outstanding balance on lines of credit	$ 25,000	$ 14,200
Unsecured Debt [Member] \| Chase Bank, N.A. [Member] \| SJW Group [Member]
Debt covenant interest charge maximum to net Income available to stockholders	1.75
Ratio of indebtedness to total capital	0.666
Line of Credit [Member] \| Revolving Credit Facility [Member] \| SJW Group [Member]
Line of Credit Facility, Interest Rate at Period End	2.27%	1.48%
Line of Credit [Member] \| Revolving Credit Facility [Member] \| Chase Bank, N.A. [Member] \| SJW Corp. and SJW Land Company [Member]
Standby letters of credit				$ 15,000
Line of Credit [Member] \| Credit Agreement [Member] \| Chase Bank, N.A. [Member] \| San Jose Water Company [Member]
Standby letters of credit				125,000
Line of Credit [Member] \| Credit Agreement [Member] \| Standby Letters of Credit [Member] \| Chase Bank, N.A. [Member] \| San Jose Water Company [Member]
Standby letters of credit				10,000
Line of Credit [Member] \| SJW Corp Credit Agreement [Member] \| Standby Letters of Credit [Member] \| Chase Bank, N.A. [Member] \| SJW Corp. and SJW Land Company [Member]
Standby letters of credit				5,000
Line of Credit [Member] \| SJWTX Credit Agreement [Member] \| Revolving Credit Facility [Member] \| Chase Bank, N.A. [Member] \| SJW Corp. and SJWTX, Inc. [Member]
Standby letters of credit				5,000
Line of Credit [Member] \| SJWTX Credit Agreement [Member] \| Standby Letters of Credit [Member] \| Chase Bank, N.A. [Member] \| SJW Corp. and SJWTX, Inc. [Member]
Standby letters of credit				$ 1,000