| Label                                        | **Element**              | Value                                                                                                                                                                                                                                                                                                                                                                       |
|----------------------------------------------|--------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Risk/Return:**                             | rr_RiskReturnAbstract    |                                                                                                                                                                                                                                                                                                                                                                        |
| Registrant Name                              | dei_EntityRegistrantName | FIDELITY INVESTMENT TRUST                                                                                                                                                                                                                                                                                                                                                   |
| Prospectus Date                              | rr_ProspectusDate        | Dec. 30,  2014                                                                                                                                                                                                                                                                                                                                                              |
| I | Fidelity Emerging Markets Discovery Fund |                          |                                                                                                                                                                                                                                                                                                                                                                        |
| **Risk/Return:**                             | rr_RiskReturnAbstract    |                                                                                                                                                                                                                                                                                                                                                                        |
| Supplement [Text Block]                      | fit_SupplementTextBlock  | **Supplement to the Fidelity Advisor® Emerging Markets Discovery Fund Institutional Class December 30, 2014 Prospectus**Effective July 1, 2015, Institutional Class will be renamed Class I. The features and policies of the class will not change. Effective October 1, 2015, the fund changed its classification from a non-diversified fund to a diversified fund. |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation 12B -Number 240 -Section 12b -Subsection 1
+ Details**Name:**dei_EntityRegistrantName**Namespace Prefix:**dei_**Data Type:**xbrli:normalizedStringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Supplement Text Block.
+ References
No definition available.
+ Details**Name:**fit_SupplementTextBlock**Namespace Prefix:**fit_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The date of the prospectus.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 1 -Subsection a -Paragraph 3
+ Details**Name:**rr_ProspectusDate**Namespace Prefix:**rr_**Data Type:**xbrli:dateItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
+ Details**Name:**rr_RiskReturnAbstract**Namespace Prefix:**rr_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_DocumentInformationDocumentAxis=fit_InstitutionalClassMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=fit_S000034264Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |