Revenue - Summary of Revenue (Detail) - EUR (€) € in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue [line items]
Total Revenue	€ 5,579	€ 6,543	€ 13,281	€ 16,464
Up-front payment amortization [member]
Revenue [line items]
Total Revenue	4,231	4,250	8,436	9,087
R&D cost reimbursement and milestone [member]
Revenue [line items]
Total Revenue	1,383	2,040	3,806	4,556
Milestone Revenue [member]
Revenue [line items]
Total Revenue	74	139	1,148	2,639
Revenue from contracts with customers [member]
Revenue [line items]
Total Revenue	5,688	6,429	13,390	16,282
Income from grants on research projects [member]
Revenue [line items]
Total Revenue	€ (109)	€ 114	€ (109)	€ 182

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