Document And Entity Information - shares	3 Months Ended
	Oct. 31, 2020	Dec. 07, 2020
Document Information Line Items
Entity Registrant Name	IDT CORP
Trading Symbol	IDT
Document Type	10-Q
Current Fiscal Year End Date	--07-31
Amendment Flag	false
Entity Central Index Key	0001005731
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Document Period End Date	Oct. 31, 2020
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	1-16371
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	22-3415036
Entity Address, Address Line One	520 Broad Street
Entity Address, City or Town	Newark
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	07102
City Area Code	(973)
Local Phone Number	438-1000
Title of 12(g) Security	Class B common stock, par value $.01 per share
Security Exchange Name	NYSE
Entity Interactive Data Current	Yes
Class A common stock
Document Information Line Items
Entity Common Stock, Shares Outstanding		1,574,326
Class B common stock
Document Information Line Items
Entity Common Stock, Shares Outstanding		23,937,301