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Stock-Based Compensation (Details Textual) |  |  |  | 1 Months Ended | 12 Months Ended
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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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- Definition The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585 + Details
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