Document and Entity Information - shares	9 Months Ended
	Jul. 04, 2015	Aug. 10, 2015
DEI [Abstract]
Entity Registrant Name	COHERENT INC
Trading Symbol	COHR
Entity Central Index Key	0000021510
Document Type	10-Q
Document Period End Date	Jul. 04, 2015
Amendment Flag	false
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--10-03
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		24,837,033