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Description of Business and Summary of Significant Accounting Policies (Details Textual) $ in Thousands | 12 Months Ended
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Jul. 31, 2017 USD ($) Segment Customer | Jul. 31, 2016 USD ($) Customer | Jul. 31, 2015 USD ($) Customer
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Number of reportable segments | Segment | 3 |  |
Investments accounted for using the equity method | $ 9,800 | $ 8,000 |
Investments accounted for using the cost method | $ 10,800 | 7,000 |
Percentage of advertising revenue, description | Over 90% of its revenues from selling its advertising inventory to advertising networks, advertising exchanges, and direct arrangements with advertisers. |  |
Restricted cash and cash equivalents | $ 10,800 | 10,500 |
Advertising expense | 17,400 | 16,500 | $ 19,700
Amortization expense related to capitalized software | 14,200 | 12,600 | 11,400
Unamortized capitalized internal use software costs | $ 22,800 | 18,800 |
Tax position ultimate settlement, percentage | 50.00% |  |
Amortization expense of intangible assets | $ 300 | 400 | 400
Intangible assets finite useful lives | 500 | 700 |
Company intends to contribute in cash |  | 6,381 |
IDT-Rafael Holdings, LLC [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Company's investment, ownership percentage in subsidiary | 90.00% |  |
IDT Financial Services Holding Limited [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Allowance for doubtful accounts included in Held for Sale | $ 2,550 | $ 861 |
Minimum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Company intends to contribute in cash | 50,000 |  |
Maximum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Company intends to contribute in cash | $ 60,000 |  |
Technology and domain names [Member] | Minimum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Amortization period | 3 years |  |
Technology and domain names [Member] | Maximum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Amortization period | 4 years |  |
Customer Lists [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Amortization period | 15 years |  |
Customer Lists [Member] | Revenues [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Number of customers | Customer | 5 | 5 | 5
Concentration risk, percentage | 12.40% | 11.20% | 11.20%
Customer Lists [Member] | Receivables [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Number of customers | Customer | 5 | 5 |
Concentration risk, percentage | 35.40% | 23.00% |
Trademark [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Amortization period | 5 years |  |
Equipment [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 7 years |  |
Equipment [Member] | Minimum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 5 years |  |
Equipment [Member] | Maximum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 20 years |  |
Buildings [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 40 years |  |
Computer Software [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 3 years |  |
Computer Software [Member] | Minimum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 2 years |  |
Computer Software [Member] | Maximum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 5 years |  |
Furniture and fixtures [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 7 years |  |
Furniture and fixtures [Member] | Minimum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 5 years |  |
Furniture and fixtures [Member] | Maximum [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of long-lived assets | 10 years |  |
Internal-use Software [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Estimated useful lives of internal-use software | Excess of one year. |  |
Long Lived Assets [Member] |  |  |
Description of Business and Summary of Significant Accounting Policies (Textual) |  |  |
Amortization expense of intangible assets with finite lives 2018 | $ 90 |  |
Amortization expense of intangible assets with finite lives 2019 | 71 |  |
Amortization expense of intangible assets with finite lives 2020 | 55 |  |
Amortization expense of intangible assets with finite lives 2021 | 43 |  |
Amortization expense of intangible assets with finite lives 2022 | $ 35 |  |

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