Revenue - Summary of Segment Revenue (Detail) - EUR (€) € in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disclosure of operating segments [line items]
Revenue from the rendering of services	€ 18	€ 444	€ 46	€ 816
Total revenue	18	444	46	816
Revenue from external customers (geographical)
Total revenue	18	444	46	816
Total revenue	18	444	46	816
USA [member]
Disclosure of operating segments [line items]
Total revenue	18	444	46	816
Revenue from external customers (geographical)
Total revenue	18	444	46	816
Total revenue	€ 18	€ 444	€ 46	€ 816

The income arising in the course of an entity's ordinary activities. Income is increases in economic benefits during the accounting period in the form of inflows or enhancements of assets or decreases of liabilities that result in an increase in equity, other than those relating to contributions from equity participants.

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+ Details