| Contingencies and commitments - Astellas Collaboration Agreement (Details) - Astellas Collaboration Agreement. - Maximum $ in Thousands | Jan. 13, 2020  USD ($) | 
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| Contingencies and commitments | |
| Milestone payments | $ 552,500 | 
| Development milestone per product developed unilaterally | |
| Contingencies and commitments | |
| Potential milestone payments | 147,500 | 
| Sales milestone for products developed unilaterally | |
| Contingencies and commitments | |
| Potential milestone payments | $ 110,000 | 
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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. No definition available. 
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