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Stock-Based Compensation Plans (Details) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward] |  |  |
Compensation expense, gross | $ 1,319,000 us-gaap_ShareBasedCompensation | $ 972,000 us-gaap_ShareBasedCompensation |
Stock Options [Member] |  |  |
Options, shares [Roll Forward] |  |  |
Outstanding, beginning of period (in shares) | 9,875 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Expired (in shares) | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Exercised (in shares) | (3,125)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Forfeited, other (in shares) | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Outstanding, end of period (in shares) | 6,750 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  | 9,875 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember
Options exercisable, end of period (in shares) | 6,750 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Options, weighted average exercise price [Roll Forward] |  |  |
Outstanding, beginning of period (in dollars per share) | $ 10.99 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Expired (in dollars per share) | $ 0 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Exercised (in dollars per share) | $ 11.14 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Forfeited, other (in dollars per share) | $ 0 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Outstanding, end of period (in dollars per share) | $ 10.92 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  | $ 10.99 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember
Options exercisable, end of period (in dollars per share) | $ 10.92 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Options, additional disclosures [Abstract] |  |  |
Outstanding, weighted average remaining contractual term, beginning of period | 0 years 1 month 6 days |  | 0 years 4 months 24 days
Outstanding, weighted average remaining contractual term, end of period | 0 years 1 month 6 days |  | 0 years 4 months 24 days
Options exercisable, weighted average remaining contractual term, end of period | 0 years 1 month 6 days |  |
Aggregate intrinsic value of outstanding stock options | 200,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Total intrinsic value of options exercised | 100,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Options granted (in shares) | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
Performance-based Shares [Member] |  |  |
Restricted and Performance Stock Grants [Abstract] |  |  |
Measuring period for performance-based shares | 3 years |  |
Award vesting rights | Selected executives and other key personnel are granted performance awards whose vesting is contingent upon meeting various performance measures with a retention feature. Performance-based shares are subject to a three-year measuring period and the achievement of performance targets and, depending upon the achievement of such performance targets, they may become vested on the third anniversary of the date of grant. |  |
Restricted Shares [Member] |  |  |
Restricted and Performance Stock Grants [Abstract] |  |  |
Award vesting rights | Restricted shares granted to employees become fully vested upon the third anniversary of the date of grant; and for selected key executives, certain additional restricted share grants vest 25% upon the attainment of age 60, 25% upon the attainment of age 63 and become fully vested upon the attainment of age 65. Restricted shares granted to directors become fully vested upon the first anniversary of the date of grant. |  |
Restricted and Performance Shares [Member] |  |  |
Restricted and performance-based stock, shares [Roll Forward] |  |  |
Beginning of period (in shares) | 749,018 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
Granted (in shares) | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
Vested (in shares) | (30,343)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
Forfeited (in shares) | (1,100)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
End of period (in shares) | 717,575 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward] |  |  |
Beginning of period (in dollars per share) | $ 24.62 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
Granted (in dollars per share) | $ 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
Vested (in dollars per share) | $ 36.14 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
Forfeited (in dollars per share) | $ 22.30 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
End of period (in dollars per share) | $ 24.13 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
Compensation expense, gross | 1,300,000 us-gaap_ShareBasedCompensation / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember | 1,000,000 us-gaap_ShareBasedCompensation / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |
Compensation expense, net of tax | 800,000 us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember | 600,000 us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |
Unamortized compensation expense | $ 10,700,000 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember |  |
Restricted and Performance Shares [Member] | Employees [Member] |  |  |
Restricted and Performance Stock Grants [Abstract] |  |  |
Estimated forfeitures (in hundredths) | 5.00%smp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEstimatedForfeituresPercentage / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember / us-gaap_TitleOfIndividualAxis = smp_EmployeesMember |  |
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward] |  |  |
Weighted average period of recognition for unrecognized compensation expense | 5 years 1 month 6 days |  |
Restricted and Performance Shares [Member] | Executives [Member] |  |  |
Restricted and Performance Stock Grants [Abstract] |  |  |
Estimated forfeitures (in hundredths) | 0.00%smp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEstimatedForfeituresPercentage / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember / us-gaap_TitleOfIndividualAxis = us-gaap_ExecutiveOfficerMember |  |
Restricted and Performance Shares [Member] | Directors [Member] |  |  |
Restricted and Performance Stock Grants [Abstract] |  |  |
Estimated forfeitures (in hundredths) | 0.00%smp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEstimatedForfeituresPercentage / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember |  |
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward] |  |  |
Weighted average period of recognition for unrecognized compensation expense | 0 years 1 month 6 days |  |
Restricted and Performance Shares [Member] | Age 60 [Member] |  |  |
Restricted and Performance Stock Grants [Abstract] |  |  |
Vesting percentage (in hundredths) | 25.00%smp_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPercentage / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember / smp_GrantAgeAxis = smp_Age60Member |  |
Restricted and Performance Shares [Member] | Age 63 [Member] |  |  |
Restricted and Performance Stock Grants [Abstract] |  |  |
Vesting percentage (in hundredths) | 25.00%smp_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPercentage / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember / smp_GrantAgeAxis = smp_Age63Member |  |
Restricted and Performance Shares [Member] | Age65 [Member] |  |  |
Restricted and Performance Stock Grants [Abstract] |  |  |
Vesting percentage (in hundredths) | 100.00%smp_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPercentage / us-gaap_AwardTypeAxis = smp_RestrictedAndPerformanceBasedSharesMember / smp_GrantAgeAxis = smp_Age65Member |  |

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- Definition The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References No definition available. + 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 Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation. + References No definition available. + Details
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- Definition The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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- Definition Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant 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 (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 The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option 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)(1)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option 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)(1)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, 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 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + 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 (d)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements. + 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)(4) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option 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)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
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