Segment information - Non-current assets by location (Details) - EUR (€) |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|---|---|---|---|
| Disclosure of geographical areas [line items] | |||
| Non-current assets | € 81,511,000 | € 357,770,000 | € 323,784,000 |
| Belgium | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | 3,887,000 | 95,686,000 | 56,209,000 |
| France | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | 5,000 | 1,438,000 | |
| The Netherlands | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | 75,890,000 | 239,454,000 | 251,230,000 |
| Switzerland | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | 92,000 | 3,247,000 | |
| United States of America | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | € 1,734,000 | € 22,533,000 | € 11,660,000 |