Significant accounting policies - Segment Reporting (Details)	12 Months Ended
Dec. 31, 2019 segment
Significant accounting policies
Number of reportable segments	2

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	glpg_IfrsNumberOfReportableSegments
Namespace Prefix:	glpg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration