Discounted Operation - Schedule Of Changes in Company's Estimated Liability (Detail) (Straight Path [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
Oct. 31, 2013
Straight Path [Member]
Schedule of Changes in Company's Estimated Liability [Abstract]
Balance, beginning of period	$ 931
Additional liability	1,624
Payments	(55)
Balance, end of period	$ 2,500

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