Document and Entity Information - USD ($)	12 Months Ended
	Jun. 30, 2018	Aug. 22, 2018	Dec. 29, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	IIVI
Entity Registrant Name	II-VI INC
Entity Central Index Key	0000820318
Current Fiscal Year End Date	--06-30
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		63,595,874
Entity Public Float			$ 2,867,219,000