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Equity Plans Restricted Stock and Deferred Restricted Stock Activity (Details) (USD $) In Thousands, except Share data, unless otherwise specified | 0 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Aug. 04, 2014 | Dec. 31, 2014 vesting_installment | Dec. 31, 2013 | Dec. 31, 2012 | Apr. 14, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |  |  |  |  |
Granted, units | 36,988us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod |  |  |  |
Performance Shares [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |  |  |  |  |
Granted, units | 19,917us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember |  |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |  |  |
Granted, wtd avg grant date fair value | 26.81us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember |  |  |  |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |  |  |  |  |
Granted, units | 17,071us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |  |  |
Number of Equal Successive Installments for Vesting of Stock Awards |  | 3sjw_NumberOfEqualSuccessiveInstallmentsForVestingOfStockAwards / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |  |  |
Granted, wtd avg grant date fair value | 24.14us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |  |  |
Restricted Stock and Deferred Restricted Stock [Member] |  |  |  |  |
Restricted and Deferred Restricted Stock Awards Outstanding [Roll Forward] |  |  |  |  |
Outstanding as of January 1, 2014, units |  | 220,364us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Issued, units |  | 71,625us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Exercised, units |  | (32,182)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Forfeited or expired |  | 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Outstanding as of December 31, 2014, units |  | 259,807us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Shares vested as of December 31, 2014, shares |  | 129,340sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Weighted Average Grant Date Fair Value [Roll Forward] [Roll Forward] |  |  |  |  |
Outstanding as of January 1, 2014, wtd avg grant date fair value |  | 16.31sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Issued, wtd avg grant date fair value |  | 26.11sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Exercised, wtd avg grant date fair value |  | 26.88sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Forfeited or expired, wtd avg grant date fair value |  | 0.00sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirationsWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Outstanding as od December 31, 2014, wtd avg grant date fair value |  | 18.56sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Shares vested as of December 31, 2014, wtd avg grant date fair value |  | 16.35sjw_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |  |  |  |  |
Nonvested as of January 1, 2014, units |  | 77,386us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Granted, units |  | 71,625us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Vested, units |  | (18,544)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Forfeited, units |  | 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Nonvested as of December 31, 2014, units |  | 130,467us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |  |  |
Nonvested as of January 1, 2014, wtd avg grant date fair value |  | 16.49us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Granted, wtd avg grant date fair value |  | 26.11us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Vested, wtd avg grant date fair value |  | 23.65us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Forfeited, wtd avg grant date fair value |  | 0.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Nonvested as of December 31, 2014, wtd avg grant date fair value |  | 20.75us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Unrecognized compensation cost |  | 1,606us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AwardTypeAxis = sjw_RestrictedStockAndDeferredRestrictedStockMember |  |  |
Period for recognition of compensation cost |  | 1 year 4 months 10 days |  |  |
Employee Stock [Member] |  |  |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |  |  |
Unrecognized compensation cost |  | 68us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember |  |  |
Employee Stock [Member] | Common Stock [Member] |  |  |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |  |  |
Number of shares reserved for issuance under the plan |  | 400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_AwardTypeAxis = us-gaap_CommonStockMember / us-gaap_PlanNameAxis = us-gaap_EmployeeStockMember |  |  |
Dividend Reinvestment and Stock Purchase Plan [Member] |  |  |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |  |  |
Number of shares reserved for issuance under the plan |  | 3,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember |  |  |
Shares issued under the plan |  | 829sjw_StockIssuedDuringPeriodSharesDividendReinvestmentAndStockPurchasePlan / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember | 3,487sjw_StockIssuedDuringPeriodSharesDividendReinvestmentAndStockPurchasePlan / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember | 1,679sjw_StockIssuedDuringPeriodSharesDividendReinvestmentAndStockPurchasePlan / us-gaap_PlanNameAxis = sjw_DividendReinvestmentAndStockPurchasePlanMember |
Minimum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 0.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |
Maximum [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 200.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |
Common Stock [Member] |  |  |  |  |
Restricted and Deferred Restricted Stock Awards, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |  |  |  |  |
Shares Deregistered Available for Issuance |  |  |  |  | 2,993,744sjw_SharesDeregisteredAvailableforIssuance / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember

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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures and Expirations, Weighted Average Grant Date Fair Value + References No definition available. + Details
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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted, Weighted Average Grant Date Fair Value + References No definition available. + Details
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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Weighted Average Grant Date Fair Value + References No definition available. + Details
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- Definition Shares Deregistered Available for Issuance + References No definition available. + Details
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- Definition Number of shares issued during the period from a dividend reinvestment and stock purchase plan (DRSPP). A dividend reinvestment and stock purchase plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity and to purchase additional shares. + References No definition available. + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Percentage of vesting of share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of non-option equity instruments exercised by participants. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of shares under non-option equity instrument agreements that were either cancelled or expired. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(3)-(4) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Net number of non-option equity instruments granted to participants. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of equity instruments other than options outstanding, including both vested and non-vested instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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