IDT Financial Services Holding Limited Assets and Liabilities Held for Sale (Details Textual) - USD ($) $ in Thousands	Jan. 31, 2019	Jul. 31, 2018
IDT Financial Services Holding Limited Assets and Liabilities Held for Sale (Textual)
Allowance for doubtful accounts	$ 1,715	$ 2,192

Amount classified as allowance for doubtful accounts attributable to disposal group held for sale or disposed of.

No definition available.

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