Discontinued Operation - Schedule Of Changes in Company's Estimated Liability (Detail) (Straight Path [Member], USD $) In Thousands, unless otherwise specified	9 Months Ended
Apr. 30, 2014
Straight Path [Member]
Schedule of Changes in Company's Estimated Liability (Textual)
Balance, beginning of period	$ 931
Additional liability	1,700
Payments	(842)
Balance, end of period	$ 1,789

Change in balance of estimated liability included in other current liabilities.

No definition available.

Name:	idt_ChangeInBalanceOfEstimatedLiabilityIncludedInOtherCurrentLiabilities
Namespace Prefix:	idt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant