v3.25.4
Intangible assets - Summary of Changes to intangible assets (Detail) - EUR (€)
€ in Thousands
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Beginning Balance € 1,629  
Ending Balance 1,582 € 1,629
Patent And Licenses [Member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Beginning Balance 1,601  
Ending Balance 1,582 1,601
Software Licenses [Member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Beginning Balance 28  
Ending Balance 0 28
Gross carrying amount [Member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Beginning Balance 3,440 3,112
Additions 247 208
Disposal (757)  
Currency translation differences (242) 120
Ending Balance 2,688 3,440
Gross carrying amount [Member] | Patent And Licenses [Member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Beginning Balance 2,367 2,052
Additions 247 202
Disposal (183)  
Currency translation differences (229) 113
Ending Balance 2,202 2,367
Gross carrying amount [Member] | Software Licenses [Member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Beginning Balance 1,073 1,060
Additions 0 6
Disposal (574)  
Currency translation differences (13) 7
Ending Balance 486 1,073
Accumulated impairment [Member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Beginning Balance (1,811) (1,589)
Additions (138) (182)
Disposal 757  
Currency translation differences 86 (40)
Ending Balance (1,106) (1,811)
Accumulated impairment [Member] | Patent And Licenses [Member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Beginning Balance (766) (629)
Additions (110) (104)
Disposal 183  
Currency translation differences 73 (33)
Ending Balance (620) (766)
Accumulated impairment [Member] | Software Licenses [Member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]    
Beginning Balance (1,045) (960)
Additions (28) (78)
Disposal 574  
Currency translation differences 13 (7)
Ending Balance € (486) € (1,045)