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Accounting Principles - Additional Information (Detail) - EUR (€)
 1 Months Ended 12 Months Ended
Jul. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2018
Disclosure of summary of significant accounting policies [line Items]          
Research tax credit reimbursement   € 7,300,000 € 5,700,000 € 4,300,000  
Tax credit reimbursement to be requested         € 9,200,000
Potential development, clinical, commercial milestones payment receivable € 100,000,000        
Non-refundable upfront payment € 10,000,000        
Deferred revenue   € 9,500,000      
Bottom of range [member] | Software [member]          
Disclosure of summary of significant accounting policies [line Items]          
Depreciation periods   1 year      
Top of range [member] | Software [member]          
Disclosure of summary of significant accounting policies [line Items]          
Depreciation periods   3 years