| Share-based compensation - Share-based Compensation Expense (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
| Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | |
| Total share-based compensation expense included in the consolidated statements of operations | ||||
| Total share-based compensation expense | $ 5,449 | $ 2,624 | $ 10,783 | $ 4,072 | 
| Research and development | ||||
| Total share-based compensation expense included in the consolidated statements of operations | ||||
| Total share-based compensation expense | 2,512 | 929 | 4,887 | 1,907 | 
| General and administrative | ||||
| Total share-based compensation expense included in the consolidated statements of operations | ||||
| Total share-based compensation expense | $ 2,937 | $ 1,695 | $ 5,896 | $ 2,165 | 
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- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- References No definition available. 
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- Details 
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- Details 
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