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Stock-Based Compensation (Details Textual)				1 Months Ended			12 Months Ended
	May. 05, 2015 shares	Jan. 06, 2014 USD ($) shares	Dec. 12, 2013 USD ($) shares	Aug. 31, 2015 USD ($) Stock	Aug. 31, 2014 Stock shares	Aug. 31, 2013 Stock shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) $ / shares shares
Stock-Based Compensation (Textual)
Stock-based compensation costs							$ 5,229,000	$ 10,758,000	$ 4,180,000
Shares issued restricted stock award (Shares) | shares
Cash Payment For Subsidiary Equity Grant							$ (1,200,000)
Chief Executive Officer [Member]
Stock-Based Compensation (Textual)
Ownership interest of company	2.80%
Officer [Member]
Stock-Based Compensation (Textual)
Ownership interest of company	0.60%
Chief Financial Officer [Member]
Stock-Based Compensation (Textual)
Ownership interest of company	0.20%
Executive Vice President [Member]
Stock-Based Compensation (Textual)
Ownership interest of company	0.30%
Stock Option [Member]
Stock-Based Compensation (Textual)
Unrecognized compensation cost							$ 800,000
Period of unrecognized compensation cost expected to be recognized							1 year 10 months 24 days
Stock-based compensation costs							$ 300,000	2,500,000	$ 400,000
Weighted-average grant date fair value of options granted | $ / shares							$ 9.67		$ 6.42
Total intrinsic value of options exercised							$ 12,000	12,000	$ 29,000
Restricted Stock Granted by IDT Corporation [Member]
Stock-Based Compensation (Textual)
Stock-based compensation costs							3,600,000	6,600,000	2,000,000
Total grant date fair value of shares vested							500,000	2,500,000	3,300,000
Restricted Stock Granted by IDT Corporation [Member] | Howard Jonas [Member]
Stock-Based Compensation (Textual)
Stock-based compensation costs							2,800,000	5,700,000
Subsidiary Equity [Member]
Stock-Based Compensation (Textual)
Unrecognized compensation cost							$ 2,700,000
Period of unrecognized compensation cost expected to be recognized							1 year 4 months 24 days
Stock-based compensation costs							$ 1,400,000	$ 1,600,000	$ 1,800,000
Fair value of the grants of equity							$ 3,300,000
Common Class B [Member]
Stock-Based Compensation (Textual)
Shares issued restricted stock award (Shares) | shares							36,000	224,000	227,000
Common Class B [Member] | IDT Energy [Member]
Stock-Based Compensation (Textual)
Common stock issued in exchange for vested deferred stock | shares					137,738	133,758
Common Class B [Member] | President [Member]
Stock-Based Compensation (Textual)
Shares issued restricted stock award (Shares) | shares			63,917
Term of restricted shares			The restricted shares vest in three years that began in January 2014.
Fair value of the restricted shares on the date of grant			$ 700,000
Common Class B [Member] | Michael Stein [Member]
Stock-Based Compensation (Textual)
Shares issued restricted stock award (Shares) | shares		29,126
Term of restricted shares		The restricted shares vest in three equal annual installments commencing on January 5, 2015.
Fair value of the restricted shares on the date of grant		$ 300,000
Common Class B [Member] | Restricted Stock [Member]
Stock-Based Compensation (Textual)
Unrecognized compensation cost							$ 9,000,000
Period of unrecognized compensation cost expected to be recognized							1 year 7 months 6 days
Common Class B [Member] | Restricted Stock [Member] | Howard Jonas [Member]
Stock-Based Compensation (Textual)
Unrecognized compensation cost							$ 8,500,000
Deferred Stock [Member] | IDT Energy [Member]
Stock-Based Compensation (Textual)
Vested deferred stock units of IDT Energy | Stock				23.6	23.6	23.6
Cash Payment For Subsidiary Equity Grant				$ 1,200,000
2011 Stock Option and Incentive Plan [Member]
Stock-Based Compensation (Textual)
Shares available for future grants, (Shares) | shares							200,000
2011 Stock Option and Incentive Plan [Member] | Common Class B [Member]
Stock-Based Compensation (Textual)
Common stock reserved for future issuance | shares							1,300,000
Additional shrares available for grants | shares	180,000

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