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Share-based Compensation - Valuation assumptions (Details) - Share options	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Valuation assumptions
Expected volatility, minimum	50.10%	49.60%	47.80%
Expected volatility, maximum	55.00%	52.10%	48.40%
Weighted average volatility	51.90%	50.80%	48.30%
Expected dividends
Risk-free rate, minimum	0.40%	1.40%	2.60%
Risk-free rate, maximum	0.70%	2.40%	2.80%
Contractual term (in years)		6 years	6 years
Minimum
Valuation assumptions
Contractual term (in years)	6 years
Maximum
Valuation assumptions
Contractual term (in years)	7 years

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- References

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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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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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.

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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.

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The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

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Rate of weighted-average expected volatility for award under share-based payment arrangement.

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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.

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