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Share-Based Compensation - Summary of Fair Value of Share Options Granted to Employees (Detail) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Expected dividend yield | 0.00% |  |
Employee Stock Option [Member] |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Risk-free interest rate, minimum | 2.49% | 1.49% | 1.15%
Risk-free interest rate, maximum | 3.01% | 2.23% | 2.18%
Expected volatility, minimum | 64.17% | 68.95% | 60.89%
Expected volatility, maximum | 70.90% | 72.24% | 68.76%
Expected dividend yield | 0.00% | 0.00% | 0.00%
Employee Stock Option [Member] | Minimum [Member] |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Expected term (in years) | 3 years | 3 years | 3 years
Employee Stock Option [Member] | Maximum [Member] |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Expected term (in years) | 6 years 3 months | 6 years 3 months | 6 years 3 months

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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 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. + References No definition available. + Details
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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. + References No definition available. + Details
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- Definition The maximum risk-free interest rate assumption that is used in valuing an option on its own shares. + References No definition available. + Details
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- Definition The minimum risk-free interest rate assumption that is used in valuing an option on its own shares. + References No definition available. + 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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- 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. + 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)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.D.2) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 + Details
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