Collaboration Agreements (Details) € in Millions	1 Months Ended	9 Months Ended
	Sep. 30, 2019 EUR (€) patient	Sep. 30, 2019 EUR (€)
AstraZeneca/MedImmune
Restructuring Cost and Reserve [Line Items]
Number of days following the expiration of the study periods end-date that the collaboration terminates		30 days
Days notice required for collaboration termination		30 days
CBG Forschungs GmbH
Restructuring Cost and Reserve [Line Items]
Days notice required for collaboration termination	30 days
Number of patients in clinical collaboration (in patients) | patient	1,200
Potential milestone payment	€ 33.0	€ 33.0
Payment term	6 years
Accrued expenses	€ 0.5