Segment information - Non-current assets by location (Details) - EUR (€) € in Thousands |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| Disclosure of geographical areas [line items] | |||
| Non-current assets | € 202,682 | € 110,645 | € 88,627 |
| Belgium | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | 133,000 | 64,000 | 47,000 |
| France | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | 54,000 | 36,000 | 34,000 |
| Croatia | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | 7,000 | 5,000 | 4,000 |
| The Netherlands | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | 8,000 | 4,000 | 4,000 |
| Switzerland | |||
| Disclosure of geographical areas [line items] | |||
| Non-current assets | € 1,000 | € 0 | € 0 |