| Share-based compensation (Tables) | 3 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Mar. 31, 2022 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Share-based compensation | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Summary of share-based compensation expense included in the unaudited consolidated statements of operations | The following table shows the total share-based compensation expense included in the unaudited consolidated statements of operations (in thousands): 
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| Summary of all stock option activity | The following table shows information about share options and options which have a nominal exercise price (similar to restricted stock units (RSUs)) granted: 
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| X | ||||||||||
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- References No definition available. 
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| X | ||||||||||
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- Definition Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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| X | ||||||||||
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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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