SHARE-BASED COMPENSATION - Assumptions used to estimate the fair values of the share options granted (Details) - Stock Options - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SHARE-BASED COMPENSATION
Contractual life of option	10 years	10 years	10 years
Dividend yield	0.00%	0.00%	0.00%
Weighted-average grant-date fair value of the options granted	$ 0.49	$ 5.69	$ 3.98
Minimum
SHARE-BASED COMPENSATION
Risk-free rate of return, minimum	1.68%	2.01%	1.31%
Estimated volatility rate, minimum	30.00%	27.00%
Fair value per ordinary share	$ 2.37	$ 3.00	$ 5.89
Maximum
SHARE-BASED COMPENSATION
Risk-free rate of return, maximum	2.63%	2.63%	1.76%
Estimated volatility rate, maximum	41.00%	38.00%
Fair value per ordinary share	$ 3.40	$ 9.51	$ 7.30

Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award.

No definition available.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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