Taxation - Summary of Unrecognized Deferred Tax Assets (Detail) - EUR (€) € in Thousands  | 
Dec. 31, 2021  | 
Dec. 31, 2020  | 
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| Major components of tax expense (income) [abstract] | ||
| Tax losses | € 132,498 | € 116,405 | 
| Deductible temporary differences | 0 | 0 | 
| Tax credits | 0 | 0 | 
| Interest carry forward | 16,986 | 12,534 | 
| Total | 149,484 | 128,939 | 
| Potential tax benefit | € 40,313 | € 34,772 | 
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- Definition Aggregate unrecognized deferred tax assets. No definition available. 
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- Definition Unrecognized deferred tax benefits potential tax benefit. No definition available. 
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- Definition Unused Interest Rate Carry Forward For Which No Deferred Tax Asset Recognized. No definition available. 
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- Definition The amount of deductible temporary differences for which no deferred tax asset is recognised in the statement of financial position. [Refer: Temporary differences [member]] Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- References No definition available. 
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- Definition The amount of unused tax credits for which no deferred tax asset is recognised in the statement of financial position. [Refer: Unused tax credits [member]] Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition The amount of unused tax losses for which no deferred tax asset is recognised in the statement of financial position. [Refer: Unused tax losses [member]] Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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