v3.26.3
Significant Events and Transactions (Details)
€ / shares in Units, $ / shares in Units, € in Millions, $ in Millions
 1 Months Ended 3 Months Ended 9 Months Ended
Sep. 29, 2026
USD ($)
patient
Aug. 03, 2026
USD ($)
$ / shares
shares
Mar. 17, 2026
Jan. 16, 2026
€ / shares
shares
Apr. 07, 2025
USD ($)
Apr. 07, 2025
EUR (€)
Jan. 31, 2026
USD ($)
Jan. 31, 2026
EUR (€)
Sep. 30, 2026
USD ($)
Dec. 31, 2025
USD ($)
Dec. 31, 2025
EUR (€)
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Jul. 27, 2026
USD ($)
Jun. 25, 2026
USD ($)
Dec. 16, 2025
Class of Stock [Line Items]                                  
Number of children enrolled in study | patient 654                                
FDA standard review period 60 days                                
Research and development expense                 $ 47.0     $ 28.6 $ 111.6 $ 83.8      
ABSA warrants                                  
Class of Stock [Line Items]                                  
Stock issued during period (in shares) | shares       34,090,004                          
Shares issued (in dollars/euro per share) | € / shares       € 0.10                          
Class of warrant or right, number of securities called by each warrant or right (in shares) | shares       1.75                          
BLA-related cost                                  
Class of Stock [Line Items]                                  
Research and development expense                 $ 4.7                
Fareva Amboise                                  
Class of Stock [Line Items]                                  
Foreign currency exchange rate, remeasurement                 1.14       1.14        
American Depositary Share                                  
Class of Stock [Line Items]                                  
Proceeds from issuance of common stock $ 50.0 $ 50.0                              
Stock issued during period (in shares) | shares   3,657,644                              
Sale of stock (in dollars per share) | $ / shares   $ 13.67                              
Common Stock                                  
Class of Stock [Line Items]                                  
Stock issued during period (in shares) | shares   18,288,220                              
Private investment in Public Equity                                  
Class of Stock [Line Items]                                  
Foreign currency exchange rate, remeasurement                                 1.17
Proceeds from issuance of common stock         $ 125.5 € 116.3 $ 94.7 € 81.0   $ 100.7 € 85.7            
Maximum                                  
Class of Stock [Line Items]                                  
Entity regulatory agency standard review, period 10 months                                
Maximum | American Depositary Share                                  
Class of Stock [Line Items]                                  
Issuance of Common Stock, Authorized Amount                             $ 150.0    
Minimum                                  
Class of Stock [Line Items]                                  
Entity regulatory agency standard review, period 6 months                                
Fareva Amboise                                  
Class of Stock [Line Items]                                  
Planned investment for commercial manufacturing                               $ 5.5  
Foreign currency exchange rate, remeasurement                 1.14       1.14        
Commercial manufacturing investment, upfront contribution                 $ 1.1       $ 1.1        
Fareva La Vallée                                  
Class of Stock [Line Items]                                  
Foreign currency exchange rate, remeasurement                 1.14       1.14        
Manufacturing and supply agreement, contractual period     8 years                            
Manufacturing and supply agreement, contractual period, renewal option     2 years