DEI Document - USD ($)	12 Months Ended
	Oct. 01, 2016	Nov. 28, 2016	Apr. 02, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	COHERENT INC
Trading Symbol	COHR
Entity Central Index Key	0000021510
Document Type	10-K
Document Period End Date	Oct. 01, 2016
Amendment Flag	false
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--10-01
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding (shares)		24,552,429
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 1,492,502,204