Operating Income - Summary of Operating Income (Detail) - EUR (€) € in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Analysis of income and expense [abstract]
Revenues			€ 202
Research tax credit	€ 9,330	€ 7,228	5,685
Subsidies	271	303	279
Other operating income	2,308	1,554
Total income	€ 11,909	€ 9,084	€ 6,166

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