| Contingencies and commitments - Alpine Collaboration Agreement (Details) - Alpine Immune Sciences Inc. - USD ($) | 1 Months Ended | 12 Months Ended | |
|---|---|---|---|
| Jun. 30, 2019 | Dec. 31, 2022 | Dec. 31, 2019 | |
| Maximum | |||
| Contingencies and commitments | |||
| Potential milestone payments | $ 288,000,000 | ||
| Research and Development Expense | |||
| Contingencies and commitments | |||
| Upfront license fees | $ 2,000,000 | $ 2,000,000 | |
| Milestone payments | $ 1,000,000 | ||
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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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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