Significant accounting policies - Employee Benefits (Details)	12 Months Ended
Dec. 31, 2017
Significant accounting policies
Percentage change of share price worse than change in Next BioTech Index	10.00%

Represents the percentage change in the share price worse than the change in the Next Biotech Index.

No definition available.

Name:	glpg_PercentageChangeOfSharePriceWorseThanChangeInNextBiotechIndex
Namespace Prefix:	glpg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration