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Cash and Cash Equivalents - Summary of Cash and Cash Equivalents by Geographic Area (Detail) - EUR (€)
€ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of geographical areas [line items]      
Cash € 48,187 € 39,799 € 62,131
Europe [member]      
Disclosure of geographical areas [line items]      
Cash 38,773 21,168  
China [member]      
Disclosure of geographical areas [line items]      
Cash 6,040 16,572  
North America [member]      
Disclosure of geographical areas [line items]      
Cash 2,725 1,317  
South America [member]      
Disclosure of geographical areas [line items]      
Cash 533 575  
Other [member]      
Disclosure of geographical areas [line items]      
Cash € 116 € 167