Stock-Based Compensation (Assump) (Details) - $ / shares |
12 Months Ended | ||
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Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Summary of weighted average assumptions used to value options granted | |||
| Grant date fair value of options (in dollars per share) | $ 14.51 | $ 9.56 | $ 19.06 |
| Volatility (as a percent) | 43.80% | 42.20% | 37.80% |
| Risk-free interest rate (as a percent) | 2.10% | 1.40% | 1.80% |
| Expected term (in years) | 6 years 3 months 18 days | 6 years 3 months 18 days | 6 years |
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- References No definition available.
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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://www.xbrl.org/2003/role/presentationRef
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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