Commitments and Contingencies (Details Textual) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Apr. 30, 2015	Jul. 31, 2014
Commitments and Contingencies (Textual)
Purchase commitment of company	$ 3,800us-gaap_PurchaseObligation
Letters of credit outstanding	3,300
Letters of credit expiration date	Apr. 30, 2016
Performance bonds outstanding	11,000idt_PerformanceBondsOutstanding
Refundable customer deposits	68,817us-gaap_CustomerDepositsCurrent	62,685us-gaap_CustomerDepositsCurrent
IDT Payment Services and IDT Financial Services [Member]
Commitments and Contingencies (Textual)
Restricted cash and cash equivalents	$ 9,500	$ 12,900

The carrying amounts of cash and cash equivalent substantially restricted.

No definition available.

Name:	idt_CashAndCashEquivalentsSubstantiallyRestricted
Namespace Prefix:	idt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	idt_CommitmentsAndContingenciesTextualAbstract
Namespace Prefix:	idt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	idt_LettersOfCreditExpirationDate
Namespace Prefix:	idt_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

In certain circumstances, the company is required to provide performance bonds in connection with its contractual commitments. Company has indemnified the surety for any expenses paid out under these performance bonds.

+ References

No definition available.

+ Details

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

- Definition

The current portion of money or property received from customers which is either to be returned upon satisfactory contract completion or applied to customer receivables in accordance with the terms of the contract or the understandings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.20)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CustomerDepositsCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement in which the entity has agreed to expend funds to procure goods or services from a supplier.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis=idt_IdtPaymentServicesAndIdtFinancialServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: