| Business combinations - Acquisition-related costs (Details) - TCR2 Therapeutics - USD ($) $ in Thousands | 6 Months Ended | 12 Months Ended | 
|---|---|---|
| Jun. 30, 2023 | Dec. 31, 2023 | |
| Business Acquisition [Line Items] | ||
| Legal, professional and accounting fees | $ 4,993 | $ 5,174 | 
| Bankers' fees | 2,172 | 2,172 | 
| Total acquisition-related costs | 7,165 | $ 7,346 | 
| Issuance costs incurred relating to the issuance of shares to TCR2 stockholders | $ 0 | 
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- Definition Amount of bankers' fees incurred to effect a business combination which costs have been expensed during the period. No definition available. 
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- Definition Amount of legal, professional and accounting fees incurred to effect a business combination which costs have been expensed during the period. No definition available. 
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- Definition Amount of issuance costs incurred relating to the issuance of shares to acquiree's stockholders, to effect a business combination which costs have been expensed during the period. No definition available. 
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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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- Definition This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Details 
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