Document and Entity Information	9 Months Ended
	Sep. 27, 2013	Oct. 28, 2013
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 27, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q3
Trading Symbol	GSIG
Entity Registrant Name	GSI GROUP INC
Entity Central Index Key	0001076930
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		33,960,019