21. Leases - Narrative (Details)	12 Months Ended
Dec. 31, 2019
Minimum
Disclosure Of Lease For Lessee [Line Items]
Lease term	1 year
Maximum
Disclosure Of Lease For Lessee [Line Items]
Lease term	4 years

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

No definition available.

Name:	afmd_IfrsLesseeLeasingArrangementsOperatingLeasesTermOfContract
Namespace Prefix:	afmd_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration