| Income taxes - Change in Valuation Allowance (Details) - USD ($) $ in Thousands | 12 Months Ended | |
|---|---|---|
| Dec. 31, 2024 | Dec. 31, 2023 | |
| Valuation allowance, beginning | $ 294,920 | $ 160,512 | 
| Foreign currency translation adjustments | (2,207) | 7,080 | 
| Net change in the valuation allowance | 14,568 | 134,408 | 
| Valuation allowance, ending | 309,488 | 294,920 | 
| Net loss | ||
| Increase in valuation allowance | 14,321 | 21,076 | 
| Other Comprehensive Income (Loss) [Member] | ||
| Increase in valuation allowance | $ 2,454 | (8,042) | 
| TCR Therapeutics Inc. | ||
| Increase in valuation allowance | $ 114,294 | |
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- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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