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Income Tax Expense - Summary of Tax Loss Carry Forward (Detail) - EUR (€)
€ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure Of Tax Loss Carryforwards [line items]    
Total € 396,763 € 399,821
Not More than Five Years [Member]    
Disclosure Of Tax Loss Carryforwards [line items]    
Total € 7,421 € 12,640
Expiration Date 2021-2025 2020-2024
More than Five Years [Member]    
Disclosure Of Tax Loss Carryforwards [line items]    
Total € 4,902 € 6,021
Expiration Date 2025 2024
No expiration [member]    
Disclosure Of Tax Loss Carryforwards [line items]    
Total € 384,440 € 381,160