| Share-based compensation - Fair Value Assumptions (Details) | 12 Months Ended | 24 Months Ended | ||
|---|---|---|---|---|
| Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2024 | |
| Assumptions used to estimate the fair values of the share options granted using the Black-Scholes option-pricing model | ||||
| Expected term (in years) | 5 years | 5 years | 5 years | |
| Expected dividend yield (as a percent) | 0.00% | 0.00% | 0.00% | |
| Minimum [Member] | ||||
| Assumptions used to estimate the fair values of the share options granted using the Black-Scholes option-pricing model | ||||
| Expected term (in years) | 6 months | |||
| Expected volatility (as a percent) | 104.00% | 84.00% | 99.00% | |
| Risk free rate (as a percent) | 3.55% | 3.27% | 0.94% | |
| Maximum [Member] | ||||
| Assumptions used to estimate the fair values of the share options granted using the Black-Scholes option-pricing model | ||||
| Expected term (in years) | 4 years | |||
| Expected volatility (as a percent) | 105.00% | 113.00% | 101.00% | |
| Risk free rate (as a percent) | 3.99% | 4.52% | 3.90% | |
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- References 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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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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/disclosureRef 
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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/disclosureRef 
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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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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