Stock and Employee Benefit Plans - Fair Value Assumptions (Details) |
12 Months Ended | |
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Dec. 31, 2017 |
Dec. 31, 2016 |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Risk free interest rate, minimum | 1.77% | 1.13% |
| Risk free interest rate, maximum | 2.22% | 2.08% |
| Dividend yield | 0.00% | 0.00% |
| Expected volatility, minimum | 75.10% | 74.90% |
| Expected volatility, maximum | 78.90% | 76.00% |
| Minimum | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Expected term | 5 years | 5 years |
| Maximum | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Expected term | 5 years 8 months 23 days | 5 years 8 months 23 days |
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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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The estimated measure of the maximum 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. No definition available.
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- Definition The estimated measure of the minimum 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. No definition available.
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- Definition The maximum risk-free interest rate assumption that is used in valuing an option on its own shares. No definition available.
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- Definition The minimum risk-free interest rate assumption that is used in valuing an option on its own shares. No definition available.
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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. No definition available.
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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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