Long-Term Debt Debt Maturity Schedule (Details)	12 Months Ended
Dec. 31, 2015 USD ($) payment	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Long-term debt	$ 384,316,000	$ 384,949,000
Mortgages [Member]
Debt Instrument [Line Items]
Loan amortization period	10 years
Number of monthly principal and interest payments \| payment	120
Fiscal Year Amortization Schedule [Abstract]
Total payment, 2016	$ 4,034,000
Total payment, 2017	11,469,000
Interest, 2016	762,000
Interest, 2017	110,000
Principal, 2016	3,272,000
Principal, 2017	$ 11,359,000
Mortgages [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rates	5.61%
Mortgages [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rates	6.09%
Mortgages [Member] \| 444 West Santa Clara Street, L.P. [Member]
Debt Instrument [Line Items]
Loan amortization period	20 years
Long-term debt	$ 2,836,000	2,947,000
Stated interest rates	5.68%
Fiscal Year Amortization Schedule [Abstract]
Total payment, 2016	$ 276,000
Total payment, 2017	276,000
Total payment, 2018	276,000
Total payment, 2019	276,000
Total payment, 2020	276,000
Total payment, thereafter	2,210,000
Interest, 2016	157,000
Interest, 2017	150,000
Interest, 2018	143,000
Interest, 2019	135,000
Interest, 2020	127,000
Interest, thereafter	42,000
Principal, 2016	119,000
Principal, 2017	126,000
Principal, 2018	133,000
Principal, 2019	141,000
Principal, 2020	149,000
Principal, thereafter	$ 2,168,000
444 West Santa Clara Street, L.P. [Member]
Debt Instrument [Line Items]
Limited partership interest percentage	70.00%
San Jose Water Company [Member] \| Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Standby letters of credit	$ 3,000,000
Fiscal Year Amortization Schedule [Abstract]
Line of Credit Facility, Renewal Term	1 year
San Jose Water Company [Member] \| Bonds [Member] \| California Pollution Control Financing Authority Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000,000	50,000,000
Stated interest rates	5.10%
San Jose Water Company [Member] \| SDWSRF loans [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,849,000	$ 1,997,000
Fiscal Year Amortization Schedule [Abstract]
Total payment, 2016	132,000
Total payment, 2017	196,000
Total payment, 2018	196,000
Total payment, 2019	196,000
Total payment, 2020	196,000
Total payment, thereafter	1,200,000
Interest, 2016	31,000
Interest, 2017	42,000
Interest, 2018	38,000
Interest, 2019	34,000
Interest, 2020	30,000
Interest, thereafter	92,000
Principal, 2016	101,000
Principal, 2017	154,000
Principal, 2018	158,000
Principal, 2019	162,000
Principal, 2020	166,000
Principal, thereafter	$ 1,108,000
San Jose Water Company [Member] \| SDWSRF loans [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rates	2.39%
San Jose Water Company [Member] \| SDWSRF loans [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rates	2.60%	2.60%

Line of Credit Facility, Renewal Term

No definition available.

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

- Definition

Loan Amortization Period

+ References

No definition available.

+ Details

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

- Definition

Long-term Debt, Maturities, Repayments of Interest after Year Five

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfInterestAfterYearFive
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Interest in Next Twelve Months

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfInterestInNextTwelveMonths
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Interest in Year Five

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfInterestInYearFive
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Interest in Year Four

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfInterestInYearFour
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Interest in Year Three

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfInterestInYearThree
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Interest in Year Two

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfInterestInYearTwo
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Principal and Interest after Year Five

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestAfterYearFive
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Principal and Interest in Next Twelve Months

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInNextTwelveMonths
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Principal and Interest in Year Five

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFive
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Principal and Interest in Year Four

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFour
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Principal and Interest in Year Three

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearThree
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Maturities, Repayments of Principal and Interest in Year Two

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearTwo
Namespace Prefix:	sjw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long-term Debt, Number of Monthly Payments

+ References

No definition available.

+ Details

Name:	sjw_LongTermDebtNumberOfMonthlyPayments
Namespace Prefix:	sjw_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt 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(a)(1))
-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 22
-Article 5

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
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

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

- Definition

The number of units or percentage investment held by one or more members or limited partners of the LLC or LP.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPMembersOrLimitedPartnersOwnershipInterest
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

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

- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ 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 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 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

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20, 22
-Article 5

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 7

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Details

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

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	dei_LegalEntityAxis=us-gaap_PartnershipInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_SubsidiariesMember
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_LongtermDebtTypeAxis=us-gaap_PublicUtilityBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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