The aggregate number of shares issued by the entity.

No definition available.

Name:	glpg_AggregateNumberOfSharesAfterTransaction
Namespace Prefix:	glpg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of aggregate share capital after the transaction.

+ References

No definition available.

+ Details

Name:	glpg_AggregateShareCapitalAfterTransaction
Namespace Prefix:	glpg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of increase in share capital arising from the issuance of new shares.

+ References

No definition available.

+ Details

Name:	glpg_IncreaseInShareCapitalDueToIssuanceOfNewShares
Namespace Prefix:	glpg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of increase in share capital arising from the issuance of warrants.

+ References

No definition available.

+ Details

Name:	glpg_IncreaseInShareCapitalDueToIssuanceOfWarrants
Namespace Prefix:	glpg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfClassesOfShareCapitalLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares issued by the entity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 106
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_106_d&doctype=Standard
-URIDate 2017-03-09

+ Details

Name:	ifrs-full_NumberOfSharesIssued
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Share capital - History (Details) - EUR (€) € in Thousands	12 Months Ended
Share capital - History (Details) - EUR (€) € in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
History of the share capital
Aggregate number of shares after transaction	50,936,778	46,256,078	39,076,342	30,299,129
Aggregate share capital after transaction	€ 275,510	€ 250,187	€ 211,390	€ 163,904
March 26, 2015
History of the share capital
Share capital increase warrants			€ 3,092
Number of shares issued			571,000
May 19, 2015
History of the share capital
Share capital increase new shares			€ 40,751
Number of shares issued			7,532,000
June 19, 2015
History of the share capital
Share capital increase warrants			€ 2,659
Number of shares issued			491,000
September 25, 2015
History of the share capital
Share capital increase warrants			€ 640
Number of shares issued			118,000
December 4, 2015
History of the share capital
Share capital increase warrants			€ 344
Number of shares issued			64,000
January 19, 2016
History of the share capital
Share capital increase new shares		€ 36,575
Number of shares issued		6,761,000
April 1, 2016
History of the share capital
Share capital increase warrants		€ 668
Number of shares issued		132,000
May 19, 2016
History of the share capital
Share capital increase warrants		€ 762
Number of shares issued		141,000
September 19, 2016
History of the share capital
Share capital increase warrants		€ 326
Number of shares issued		60,000
November 28, 2016
History of the share capital
Share capital increase warrants		€ 467
Number of shares issued		86,000
April 6, 2017
History of the share capital
Share capital increase warrants	€ 1,337
Number of shares issued	247,000
April 21, 2017
History of the share capital
Share capital increase new shares	€ 23,331
Number of shares issued	4,313,000
June 20, 2017
History of the share capital
Share capital increase warrants	€ 281
Number of shares issued	52,000
September 21, 2017
History of the share capital
Share capital increase warrants	€ 152
Number of shares issued	28,000
November 23, 2017
History of the share capital
Share capital increase warrants	€ 222
Number of shares issued	41,000