Collaboration Agreements (Details) € in Millions	12 Months Ended
	Dec. 31, 2019 EUR (€) patient
Guarantor Obligations [Line Items]
Potential milestone payment	€ 33.0
Potential milestone payment terms (in years)	6 years
Accrued expenses	€ 0.5
CBG Forschungs GmbH
Guarantor Obligations [Line Items]
Number of patients in clinical collaboration (in patients) | patient	1,200