Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ 154,557
Dividends declared ($0.47 per share)			(11,677)
Restricted Class B common stock purchased from employees			(61)
Transfer of right to receive equity to Howard S. Jonas			(40)
Consolidation of Lipomedix Pharmaceuticals Ltd.			558
Distributions to noncontrolling interests			(1,023)
Stock-based compensation			2,842
Comprehensive loss:
Net loss	$ (3,230)	$ (4,452)	(3,336)	$ 19,099
Other comprehensive income	204	1,159	16	(1,307)
Comprehensive loss	(3,026)	$ (3,293)	(3,320)	$ 17,792
Ending Balance	26,917		26,917
Attributable to IDT Corporation [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			145,734
Dividends declared ($0.47 per share)			(11,677)
Restricted Class B common stock purchased from employees			(61)
Transfer of right to receive equity to Howard S. Jonas
Consolidation of Lipomedix Pharmaceuticals Ltd.
Distributions to noncontrolling interests
Stock-based compensation			2,842
Comprehensive loss:
Net loss			(4,034)
Other comprehensive income			16
Comprehensive loss			(4,018)
Ending Balance	26,554		26,554
Noncontrolling Interests [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			8,823
Dividends declared ($0.47 per share)
Restricted Class B common stock purchased from employees
Transfer of right to receive equity to Howard S. Jonas			(40)
Consolidation of Lipomedix Pharmaceuticals Ltd.			558
Distributions to noncontrolling interests			(1,023)
Stock-based compensation
Comprehensive loss:
Net loss			698
Other comprehensive income
Comprehensive loss			698
Ending Balance	$ 363		$ 363