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Share-Based Payments - Amounts for Employee Options Granted were Estimated on Date of Grant Using Modified Black-Scholes Option Pricing Model (Details) - Employee Stock Purchase Plan | 12 Months Ended
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Dec. 31, 2018 $ / shares
March 25, 2015 (1) |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Per share weighted average fair value (in dollars per share) | $ 8.17
Risk free interest rate | 0.94%
Dividend yield | 1.78%
Expected life (in years) | 3
Share price volatility | 16.00%
March 25, 2015 (2) |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Per share weighted average fair value (in dollars per share) | $ 7.08
Risk free interest rate | 0.60%
Dividend yield | 1.78%
Expected life (in years) | 2
Share price volatility | 16.00%
March 25, 2016 (1) |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Per share weighted average fair value (in dollars per share) | $ 7.97
Risk free interest rate | 1.04%
Dividend yield | 1.88%
Expected life (in years) | 3
Share price volatility | 4.21%
March 25, 2016 (2) |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Per share weighted average fair value (in dollars per share) | $ 7.00
Risk free interest rate | 0.87%
Dividend yield | 1.88%
Expected life (in years) | 2
Share price volatility | 2.44%
April 28, 2017 |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Per share weighted average fair value (in dollars per share) | $ 6.69
Risk free interest rate | 1.44%
Dividend yield | 1.83%
Expected life (in years) | 3
Share price volatility | 3.67%
April 28, 2017 (2) |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Per share weighted average fair value (in dollars per share) | $ 8.70
Risk free interest rate | 1.44%
Dividend yield | 1.83%
Expected life (in years) | 3
Share price volatility | 3.67%
April 28, 2017 (3) |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Per share weighted average fair value (in dollars per share) | $ 8.70
Risk free interest rate | 1.26%
Dividend yield | 1.83%
Expected life (in years) | 2
Share price volatility | 3.52%

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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://fasb.org/us-gaap/role/ref/legacyRef -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=109197908&loc=d3e5070-113901 + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- 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
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