| Share based compensation - Unrecognized Compensation Cost (Details) | 12 Months Ended | 
|---|---|
| Dec. 31, 2023  USD ($) | |
| Share based compensation | |
| Unrecognized compensation cost | $ 9,702,000 | 
| Expected weighted-average cost recognition period (in years) | 2 years 4 months 24 days | 
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- References No definition available. 
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- Definition Weighted-average period over which cost not yet recognized is expected to be recognized for 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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- Definition Amount of cost to be recognized for option under share-based payment arrangement. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef 
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