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Personnel expenses - Additional Information (Detail) - EUR (€)
€ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Classes of employee benefits expense [abstract]      
Post-employment benefit expense, defined contribution plans € 200 € 100 € 100
Employee health insurance cost 400 300 400
Social security contributions 1,700 1,300 1,000
other miscellaneous expenses € 100 € 70 € 200