Share based compensation - Fair value of options granted that are estimated using binomial model (Details) - 2021 Option Plan - $ / shares	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share based compensation
Risk-free rate of return, minimum	3.79%	1.63%	1.20%
Risk-free rate of return, maximum	3.88%	3.83%	1.65%
Volatility, minimum	44.37%	44.18%	44.03%
Volatility, maximum	44.95%	45.07%	44.47%
Expected dividend yield	0.00%	0.00%	0.00%
Expected terms	10 years	10 years	10 years
Minimum
Share based compensation
Fair value of underlying ordinary share	$ 3.16	$ 7.57	$ 6.99
Maximum
Share based compensation
Fair value of underlying ordinary share	$ 8.02	$ 9.30	$ 7.55

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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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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- Definition

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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- 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

Price of a single share of a number of saleable stocks of a company.

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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.

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