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Share-Based Payments - Summary of Stock Options Valuation Assumptions (Detail)
9 Months Ended
Sep. 30, 2021
€ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Weighted average share price at grant date in € € 10.75
Weighted average risk-free interest rate (0.53%)
Weighted average expected term (in years) 3 years 2 months 15 days
Dividend yield
Weighted average fair value of stock options in € € 0
Weighted Average [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Weighted average share price at grant date in € € 9.3
Weighted average expected volatility 90.90%
Weighted average risk-free interest rate (0.36%)
Weighted average expected term (in years) 6 years
Weighted average fair value of stock options in € € 6.9