Statement Of Cash Flows [Abstract]
| Concept | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | 2022-01-01 to 2022-12-31 | As at 2021-12-31 | 
|---|---|---|---|---|---|
| Statement of cash flows [abstract] | |||||
| Cash flows from (used in) operating activities [abstract] | |||||
| Cash flows from (used in) operations | 
                                                732,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
                                                2,684,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
| Income taxes paid (refund), classified as operating activities | 
                                                0
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
                                                0
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
| Cash flows from (used in) operating activities | 
                                                698,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
                                                2,701,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
| Cash flows from (used in) investing activities [abstract] | |||||
| Cash flows from losing control of subsidiaries or other businesses, classified as investing activities | 
                                                0
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
                                                105,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
| Purchase of property, plant and equipment, classified as investing activities | 
                                                11,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
                                                6,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
| Cash flows from (used in) investing activities | 
                                                11,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
                                                99,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
| Cash flows from (used in) financing activities [abstract] | |||||
| Cash flows from (used in) financing activities | 
                                                0
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
                                                5,978,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
| Increase (decrease) in cash and cash equivalents after effect of exchange rate changes | 
                                                709,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
                                                3,376,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
| Cash and cash equivalents | — | 
                                                2,669,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                3,378,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                2,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             |