Document And Entity Information - USD ($)	12 Months Ended
	Jul. 31, 2020	Dec. 17, 2020	Jan. 31, 2020
Document Information Line Items
Entity Registrant Name	IDT CORP
Trading Symbol	IDT
Document Type	10-K/A
Current Fiscal Year End Date	--07-31
Entity Public Float			$ 145,900,000
Amendment Flag	true
Amendment Description	IDT Corporation (the “Company”) is filing this Amendment No. 1 on Form 10-K/A (the “Amendment”) to the Company’s annual report on Form 10-K for the year ended July 31, 2020 (the “Form 10-K”), filed with the Securities and Exchange Commission on October 14, 2020 (the “Original Filing Date”), solely to furnish Exhibit 4.2 to the Form 10-K in accordance with Item 601(b)(4) of Regulation S-K. Exhibit 4.2 provides a description of each class of securities of the Company registered pursuant to Section 12 of the Securities Exchange Act of 1934.No other changes have been made to the Form 10-K. Except as indicated otherwise herein, this Amendment speaks as of the Original Filing Date, does not reflect events that may have occurred subsequent to the Original Filing Date, and does not modify or update in any way disclosures made in the Form 10-K.
Entity Central Index Key	0001005731
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Well-known Seasoned Issuer	No
Document Period End Date	Jul. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Document Annual 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 $0.01 per share
Security Exchange Name	NYSE
Entity Interactive Data Current	Yes
Class B common stock
Document Information Line Items
Entity Common Stock, Shares Outstanding		23,942,301
Class A common stock
Document Information Line Items
Entity Common Stock, Shares Outstanding		1,574,326