Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2017	Oct. 09, 2017	Jan. 31, 2017
Entity Registrant Name	IDT CORP
Entity Central Index Key	0001005731
Amendment Flag	false
Trading Symbol	IDT
Current Fiscal Year End Date	--07-31
Document Type	10-K
Document Period End Date	Jul. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 390.7
Class A Common Stock
Entity Common Stock Shares Outstanding		1,574,326
Class B Common Stock
Entity Common Stock Shares Outstanding		23,267,081