Stock Plans - Fair value of stock options (Details) - USD ($) |
3 Months Ended | 9 Months Ended | ||||||||||
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Sep. 30, 2019 |
Sep. 30, 2018 |
Sep. 30, 2019 |
Sep. 30, 2018 |
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| Stock Plans | ||||||||||||
| Weighted-average risk-free interest rate | 0.00% | 2.90% | 2.20% | 2.70% | ||||||||
| Expected dividend payments | $ 0 | $ 0 | $ 0 | $ 0 | ||||||||
| Expected holding period (years) | 6 years 4 months 24 days | [1] | 5 years 4 months 24 days | 6 years 4 months 24 days | ||||||||
| Weighted-average volatility factor | 0.00% | [2] | 0.91% | [2] | 0.94% | 0.89% | ||||||
| Estimated forfeiture rates for options granted | 0.00% | [3] | 25.00% | [3] | 21.00% | 26.00% | ||||||
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- Definition Estimated forfeiture rates for options granted to management. No definition available.
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- References No definition available.
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- Definition The estimated amount of dividends to be paid to holders of the underlying shares (expected dividends) over the option's term. Dividends are taken into account because payment of dividends to shareholders reduces the fair value of the underlying shares, and option holders generally do not receive dividends. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Rate of weighted-average expected volatility for award under share-based payment arrangement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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