Share-Based Compensation - Weighted Average Assumptions Use in Calculation of Fair Value for Service, Performance Condition, and Market and Performance Condition Awards (Detail) |
12 Months Ended | ||
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Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| SARs [Member] | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Expected volatility | 49.20% | 49.60% | 48.70% |
| Dividends yield | 0.00% | 0.10% | 1.60% |
| Expected term | 6 years | 6 years | 5 years 9 months 18 days |
| Risk-free interest rate | 2.20% | 1.20% | 1.60% |
| Performance condition awards [Member] | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Expected volatility | 49.60% | 49.60% | 48.80% |
| Dividends yield | 0.00% | 0.00% | 1.60% |
| Expected term | 6 years 1 month 6 days | 6 years | 5 years 9 months 18 days |
| Risk-free interest rate | 2.20% | 1.20% | 1.60% |
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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 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 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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