Segmentation - Summary of the Amount of Total Non-Current Assets (Detail) - EUR (€) € in Thousands  | 
Dec. 31, 2021  | 
Dec. 31, 2020  | 
|---|---|---|
| Disclosure of Non Current Assets By Country [Line Items] | ||
| Non-current assets | € 80,231 | € 58,087 | 
| The Netherlands | ||
| Disclosure of Non Current Assets By Country [Line Items] | ||
| Non-current assets | 59,047 | 38,056 | 
| Belgium | ||
| Disclosure of Non Current Assets By Country [Line Items] | ||
| Non-current assets | 7,049 | 5,885 | 
| Germany | ||
| Disclosure of Non Current Assets By Country [Line Items] | ||
| Non-current assets | 13,568 | 14,134 | 
| Other | ||
| Disclosure of Non Current Assets By Country [Line Items] | ||
| Non-current assets | € 567 | € 12 | 
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- Definition Disclosure of Non Current Assets By Country No definition available. 
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- Definition Non-current assets excluding non-current financial assets and deferred tax assets. No definition available. 
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